,transcriber's ,notes3 ,underscores 80 before and after a word or phrase indicate italics in the original text4 ,equal signs 80 before and after a word or phrase indicate bold in the original text4 ,small capitals have been converted to ,,solid capitals4 ,illustrations and footnotes have been moved so they do not break up paragraphs4 ,deprecated spellings have been preserved4 ,typographical and punctuation errors have been silently corrected4 ,,the ,,soil ,,solution ,published by ,the ,chemical ,publishing ,co4 ,easton1 ,penna4 ,publishers of ,scientific ,books ,engineering ,chemistry ,portland ,cement ,agricultural ,chemistry ,qualitative ,analysis ,household ,chemistry ,chemists' ,pocket ,manual ,metallurgy1 ,etc4 ,the ,soil ,solution ,the ,nutrient ,medium for ,plant ,growth ,by ,,frank ,k4 ,,cameron ,in ,charge1 ,physical and ,chemical ,investigations1 ,bureau of ,soils1 ,u4 ,s4 ,department of ,agriculture ,,easton1 ,,pa43 ,,the ,,chemical ,,publishing ,,co4 #aiaa ,,london1 ,,england3 ,,williams ,,norgate #ad ,,henrietta ,,street1 ,,covent ,,garden1 ,w4 ,c4 ,,copyright1 #aiaa1 ,,by ,,edward ,,hart ,preface4 ,it has long been the custom to regard soil chemistry from one of two diametrically opposed points of view4 ,either1 it has been considered extremely simple1 or complex and hopelessly difficult4 ,in either case the impression has generally prevailed that practical work in soil chemistry consists in treating the soil with some solvent or other and analyzing the resulting solution for 8available0 plant food elements2 in other words1 that the chemist's role in soil studies is merely that of an analyst4 ,soil chemistry is complex1 but not by any means hopelessly so4 ,unfortunately1 the complexity of most of the problems presented has deterred the student of pure chemistry from attacking them1 and because they do not offer any material pecuniary rewards1 they have not appealed strongly to the investigator in applied chemistry4 ,investigations in soil chemistry1 for their own sake1 or for the sole purpose of increasing the sum total of human knowledge concerning the phenomena taking place in the soil1 have been comparatively rare4 ,the subject has generally been regarded from the analytical point of view and as incidental to agronomic studies4 ,one purpose of this little book is to show the investigator in chemistry who is not limited by the condition that his work must bring some personal financial return1 that the soil and its problems offer a field for his efforts quite worthy of ranking along-side the most interesting branches of pure chemistry1 as well as being of the very highest importance to the development of the welfare of the human race4 ,another purpose is to point out the line of attack upon the problems of soil chemistry which at this time offers the largest opportunity for results4 ,in how far the details of the story in the following pages are correct1 time with its further investigations will tell4 ,in a sense1 the correctness of the details is of secondary importance4 ,it is of the first importance1 however1 that there should be a general recognition that soil phenomena are essentially dynamic in character1 and that the investigation of the properties of the soil solution and its relation to crop production is a procedure certain to yield results of positive value4 ,again1 it is a purpose of this book to make available for students of agriculture1 a systematic outline of the work so far accomplished in this particular field4 ,it is to the students of to-day from whom are to come the investigations of the near future that the book is particularly addressed4 ,some of the details presented in the following pages are matters on which opposed opinions are now held strongly by different authorities1 and to the unbiased minds of the coming investigators must be left the decision as to how closely the truth has been approximated in what is written to-day4 ,the field of effort covered by this book is one in which there is an increasing activity1 and new facts and deductions will inevitably bring modifications to present opinions4 ,to encourage this further acquisition of knowledge is the main purpose of the book4 ,the material brought together in this book has been presented to the faculties and students of several of our ,agricultural ,colleges1 in the form of a short course of lectures4 ,in large part1 moreover1 it has been published in ,volume ,,xiv of the ,journal of ,physical ,chemistry4 ,to make it accessible to and more easily read by one familiar with the progress of technical soil investigations1 it has been recast in its present form4 ,it has been assumed that the reader will have a fair working knowledge of the concepts of modern chemistry4 ,nevertheless1 an effort has been made to avoid technical terms so far as this can be done without undue sacrifice of lucidity of expression4 ,free references have been made to the bulletins of the ,bureau of ,soils1 ,u4 ,s4 ,department of ,agriculture1 because they are generally accessible to the ,american student1 and because in them will be found detailed discussions and bibliographical material pertinent to the subjects outlined here4 ,to his coworkers1 the author is indebted for many criticisms and suggestions2 and more especially in the making of the book is he indebted to ,mr4 ,s4 ,c4 ,stuntz4 ,washington1 ,d4 ,c4 #aiaa4 ,table of ,contents4 ,,page ,preface iii ,i4 ,the ,soil #a ,,ii4 ,soil ,management or ,control #d ,,iii4 ,soil ,analysis and the ,historical ,methods of ,soil ,investigation #h ,,iv4 ,the ,plant-,food ,theory of ,fertilizers #af ,v4 ,the ,dynamic ,nature of ,soil ,phenomena #ah ,,vi4 ,the ,film ,water #bd ,,vii4 ,the ,mineral ,constituents of the ,soil ,solution #ca ,,viii4 ,absorption by ,soils #ei ,,ix4 ,the ,relation of ,plant ,growth to ,concentration #gj ,x4 ,the ,balance ,between ,supply and ,removal of ,mineral ,plant ,nutrients #ge ,,xi4 ,the ,organic ,constituents of the ,soil ,solution #gi ,,xii4 ,fertilizers #aje ,,xiii4 ,alkali #aaj ,index #abg ,,an ,,introduction ,,to ,,the ,,study ,,of ,,the ,,soil ,,solution4 ,chapter ,i4 ,,the ,,soil4 ,the soil1 or that part of the land surface of the earth adapted to the growth and support of crops1 is a heterogeneous mixture composed of solids1 gases and a liquid1 and containing living organisms4 ,there are present3 mineral debris from rock degradation and decomposition2 organic matter from the degradation and decomposition of former plant and animal tissues2 the soil atmosphere1 always richer in carbon dioxide and water vapor and possibly other gases than the atmosphere above the soil2 living organisms1 such as various kinds of bacteria and fungi1 with the products of their activities1 notably the 8nitrogen carriers0 and the enzymes2 and finally the soil moisture1 a solution of products yielded by the above components and in equilibrium or approaching equilibrium with the solids and gases with which it is in contact4 ,in its relation to crop plants1#a that part of the soil of immediate importance is the soil moisture4 ,from this solution the plants1 through their roots1 draw all the material involved in their growth1 except the carbon dioxide absorbed through their leaves4 ,the soil solution is the natural nutrient medium from which the plants absorb the mineral constituents which have been shown to be absolutely essential to their continued existence and development4 ,and from this solution plants sometimes absorb dissolved organic substances1 but such absorptions are probably adventitious and incidental to the growth of the plant in a particular environment4 ,while it appears certain that no organic substance in the nutrient medium is necessary to the maintenance of plant growth1 nevertheless organic substances are probably always present under natural conditions4 ,they may or may not be absorbed by the plant and may affect it beneficially or otherwise4 #a ,by crop plants are meant the ordinary green plants employed in agriculture4 ,as is well-known1 the fungi as well as certain parasitic and saprophytic non-green seed plants obtain their nutriment in a very different way from ordinary green crop plants4 ,the study of the soil solution is of the first importance in the investigation of the relation of the soil to plant growth1 and in the following pages there is given an outline of our present knowledge of the chemical principles involved1 with such discussion of the physical and biological factors as is essential to an orderly presentation of the subject4 ,to understand clearly the relations of the soil solution to the soil as a whole and to the plant which it nourishes1 it is desirable to consider some attributes of soils in general4 ,every soil1 no matter of what type it may be1 is a complex system4 ,in it various processes are continually in operation1 excepting possibly in the extreme case when it remains frozen for a time at some definite temperature4 ,the resultant or summation of these processes1 whether expressed in plant production or otherwise1 will vary from time to time1 both quantitatively and in direction2 for instance1 as to the amount and kinds of plant growth it produces4 ,that is to say1 any particular soil area is seemingly an organic entity1 functioning according to its own inherent properties1 but subject to the modifying influences of environment1 as by exceptional climatic extremes1 flood1 fire1 and especially by artificially imposed agencies of control4 ,from the practical point of view the problem of the soil in its relation to crop production is like the problem of the factory or of any other industrial endeavor1 in that it is a problem of management or control4 ,the soil possesses this distinction1 however1 that it is both the raw material and the factory4#b ,the processes involved are physical1 chemical and biological1 are always numerous and interdependent1 and are never 7speaking generally7 exactly the same1 so that each soil possesses marked individuality4 ,no matter how soils may be classified1 as for instance into provinces1 series and types1#c the fact remains that the soil of the individual field has properties which give it a crop-producing power1 an adaptation to a specific crop or crop rotation1 or a responsiveness to cultural treatment1 which can not be anticipated in any other field4 ,consequently1 there is no possibility of reducing soil management or agriculture to the state of an exact science4 ,that is to say1 scientific investigation of the problems involved cannot be expected to yield absolute results1 although furnishing the best possible basis on which to form judgments4 ,soil management1 like other agricultural practices1 is an art1 more or less well founded on scientific principles1 perhaps1 but susceptible of much higher development as the scientific principles involved become better understood4 #b ,according to ,s4 ,w4 ,johnson--,some points of agricultural science1 ,am4 ,jour4 ,sci4 7#b71 #bh1 #ga-he 7#ahei7--8,the soil 7speaking in the widest sense7 is then not only the ultimate exhaustless source of mineral 7fixed7 food1 to vegetation1 but it is the storehouse and conservatory of this food1 protecting its own resources from waste and from too rapid use1 and converting the highly soluble matters of animal exuvi as well as of artificial refuse 7manures7 into permanent supplies40 #c ,for definitions1 see ,soil ,survey ,field ,book1 #aijf1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 of ,agriculture1 pp4 #ae-bd4 ,on the ground that experience has shown that genetic classifications are the ones which have generally persisted and proved the most useful1 objection might be made to the classification just cited4 ,but a careful inspection of the results of the ,soil ,survey by the ,u4 ,s4 ,department of ,agriculture will show that while not categorically stating the fact1 to all intents and purposes it has employed a genetic classification4 ,this is exemplified by the fact that its delineation of soil provinces corresponds quite closely with the recognized physiographic provinces of the ,united ,states4 ,see map accompanying ,soils of the ,united ,states1 by ,milton ,whitney1 ,bull4 ,no4 #ee ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aiji4 ,chapter ,,ii4 ,,soil ,,management ,,or ,,control4 ,aside from such devices as greenhouses1 wind-breaks1 etc41 which have a local application only1 there are three general methods of soil control3 tillage methods1 such as plowing and harrowing2 rotation of crops2 and the use of soil amendments or 8fertilizers40 ,the existing knowledge regarding tillage methods is generally considered to be fairly satisfactory4 ,the purposes are well understood1 namely1 to break up and 8fine0 the soil1#d to keep down weeds1 and by forming mulches to decrease the loss of water by evaporation4 ,not much increase is being made in our theoretical knowledge of this subject1 although mechanical improvements in the implements of tillage are being and will undoubtedly continue to be made4 #d ,actually1 to granulate the soil4 8,fine0 would seem to be a misnomer1 but its agricultural significance is well understood1 and it has the sanction of long usage in the literature4 ,the existing knowledge concerning crop rotations is fairly extensive1 but it is almost entirely empirical4 ,some at least of the purposes served by a rotation of crops are fairly well known1 such as the elimination of weeds or lower types of parasitic growth associated with particular crops2 the introduction of humus by a grass crop or a green manure crop1 especially by the ,leguminosae with their symbiotic ,azobacteria2 the improvement in the structure or arrangement of the soil particles by alternating deep-rooted and shallow-rooted crops2 the avoidance of continually growing a crop in the presence of its own excreta1 products of decay1 etc42 and lastly1 economic and market considerations4 ,the existing knowledge of fertilizers1 in spite of a vast amount of work and an enormous literature1 is still very meagre and it also is almost entirely empirical2 and this because studies on the subject have been dominated for three-quarters of a century by one theory almost to the exclusion of any other4 ,the exponents of this theory have generally assumed that the action of fertilizers is on the plant rather than on the soil1 and is independent of other factors4 ,that is1 while it is admitted that other factors influence plant growth1 it has been held that the effect of the fertilizer is not to modify the influence of the other factors but to directly influence the plant by increasing its food supply4 ,as a consequence1 it has also been generally assumed that the influence of fertilizers is additive1 that is1 the increase in yield of crop is proportional to the increase in fertilizer added1 and the increase in yield produced by adding two fertilizers is the sum of the increases which would have been produced by each alone4 ,in this form the theory is essentially a quantitative one1 and fertilizer practice should be easily susceptible of control by chemical analyses4 ,but the large mass of data obtained from plot experiments shows that fertilizer effects are not additive4 ,indeed1 the addition of some one or more fertilizer constituent is sometimes followed by a decreased yield4 ,for example1 about #bj per cent4 of the trials of fertilizers on soils growing corn and reported by the ,american ,state ,experiment ,stations show a decreased yield4 ,and furthermore1 in spite of the quantitative character of the theory1 and the numerous analyses of soils and of plants which have been made1 there is yet lacking any authoritative method for determining in quantitative terms the fertilizer needs of a soil4 ,that analytical methods have a very restricted value in indicating even qualitatively the fertilizer needs of the soil is evidenced by the fact that within the past few years a number of the ,state ,experiment ,stations have publicly announced their unwillingness to undertake them4#e #e ,in this connection see3 ,the texture of the soil1 by ,l4 ,h4 ,bailey1 ,cornell ,university ,agr4 ,expt4 ,sta41 ,bull4 ,no4 #aai 7#ahif72 ,suggestions regarding the examination of lands1 by ,e4 ,w4 ,hilgard1 ,university of ,california1 ,college of ,agriculture1 ,circ4 ,no4 #be1 7#aijf72 ,chemical analysis of soils1 by ,william ,p4 ,brooks1 ,massachusetts ,agr4 ,expt4 ,sta4 ,circ4 ,no4 #aa1 7#aijg72 ,testing soils for fertilizer needs1 by ,f4 ,w4 ,taylor1 ,new ,hampshire ,agr4 ,expt4 ,sta41 ,circ4 ,no4 #b1 7#aijh72 ,the uses and limitations of soil analysis1 by ,j4 ,t4 ,willard1 ,the ,industrialist4 ,kansas ,state ,agricultural ,college1 #cd1 #bia1 7#aijh72 ,soil analysis1 by ,wm4 ,frear1 ,pennsylvania ,agr4 ,expt4 ,sta41 ,chem4 ,circ4 ,no4 #a2 ,how to determine the fertilizer requirements of ,ohio soils1 by ,chas4 ,e4 ,thorne1 ,ohio ,agr4 ,expt4 ,sta41 ,circ4 ,no4 #gi1 7#aijh72 ,concerning work which the station can and cannot undertake for residents of the state1 by ,joseph ,l4 ,hills1 ,vermont ,agr4 ,expt4 ,sta41 ,circ4 ,no4 #c1 7#aiji74 ,the common procedure has been to define some arbitrary percentage limit in the soil1 below which the soil is supposed to require fertilizers4 ,but the amount of fertilizer to be applied is suggested on the indefinite basis of 8experience40 ,thus1 ,hilgard1 in an interesting discussion of this subject1#f quotes ,dyer as showing that 8on ,rothamsted soils of known productiveness or manurial condition1 it appears that when the citric acid extraction yields as much as #j4jje per cent4 of potash and #j4jaj per cent4 of phosphoric acid1 the supply is adequate for normal crop production1 so that the use of the above substances as fertilizers would be1 if not ineffective1 at least not a profitable investment40 ,hilgard himself sets limits as determined by strong hydrochloric acid digestion2 thus a soil containing upwards of #j4de per cent4 7,k,o7 does not need this substance as a fertilizer1 while one containing below #j4be per cent4 does need it at once1 and intermediate percentages indicate that potash fertilizers would probably be profitable2 the corresponding upper and lower limits for phosphoric acid are set at #j4aj per cent4 and #j4je per cent4 ,but ,hilgard points out that various things1 such as the content of lime1 or the texture of the soil1 may materially alter these limits4 ,in a very interesting set of experiments in which white mustard was grown in various soils1 and these same soils diluted with various amounts of dune sand which had previously been extracted with strong hydrochloric acid1 he found that the plants did best when the soils had been diluted with four times their weight of the extracted sand4 ,this was the case even with a pulverulent sandy loam2 and with a black adobe1 the best results were obtained when the diluted soil contained but #j4ae per cent4 potash 7,k,o7 and #j4jd per cent4 phosphoric acid 7,p,o74 ,it also appears that ,hilgard regards soil analyses of value only in the case of virgin soils or soils which have been out of cultivation1 and in common with other authorities1 he fails to point out how to determine the amount of fertilizer needed by lands4 #f ,soils by ,e4 ,w4 ,hilgard1 #aijf1 p4 #cci1 et seq4 ,it is clear1 therefore1 that the principles underlying the practice or art of soil management and crop rotation are in a state of development far from satisfactory1 and scientific methods of soil control yet wanting4#g ,recent activities in soil investigations1 however1 justify the hope that much improvement is to be anticipated1 and the application of the modern methods of physical1 chemical1 and biological research to the soil problem promises a sure and probably rapid advance in this branch of applied science4 #g ,it should1 of course1 be borne in mind that soil factors are not the only ones in crop production4 ,control by seed selection1 breeding of standard types of plants1 etc41 may be1 and probably is1 more highly developed than control by soil factors4 ,the same might possibly be claimed for moisture supply in irrigated areas2 but on the other hand1 such factors as the bacterial and lower life processes in the soil are generally under little or no control1 and as a rule the amount and distribution of sunlight under none at all4 ,a notable effort has been made in the last case with shade-grown tobacco 7see ,bulletins ,nos4 #bj and #ci1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture7 and a few cases are known where shade-crops are employed1 but not in general agriculture4 ,chapter ,,iii4 ,,soil ,,analysis ,,and ,,the ,,historical ,,methods ,,of ,,soil ,,investigation4 ,owing to the labors of ,davy1 ,boussingault1 de ,saussure1 ,liebig1 ,sachs1 ,knop1 ,salm-,horstmar1 and other scarcely less distinguished savants1 it has been clearly shown that growing plants need certain mineral elements in order to maintain their metabolic functions1 and that these mineral elements can be obtained1 under normal conditions1 from the soil4 ,all subsequent investigation has confirmed these statements and they can now be accepted as facts with as much assurance as any known law of nature4 ,the determination and formulation of these two fundamental facts came at a time when analytical chemistry was being rapidly developed and was finding wide and useful applications in numerous fields of activity4 ,it was natural1 therefore1 that analytical chemistry should be enlisted in this new field of work1 obviously of the first importance to the welfare of mankind4 ,it was early found1 however1 that the chemical analysis of a soil fails to explain its relative productivity4 ,in other words the content of a soil with respect to potash1 phosphoric acid1 or other mineral plant-food constituent1 bears no necessary relation to its crop-producing power4 ,many cases were found where one soil 8analyzed well0 but did not produce as large a crop as another soil which 8analyzed poor40#h ,to meet this difficulty a subsidiary hypothesis was brought forward1 which rapidly gained general acceptance although lacking experimental support4 #h ,see also1 ,die ,aufnahme der ,nhrstoffe aus dem ,boden durch die ,pflanzen1 von ,j4 ,knig und ,e4 ,haselhoff1 ,landw4 ,jahrb41 #bc1 #ajji1 #ajcj1 7#ahid74 ,this hypothesis supposes that the mineral constituents of the soil are present in two different chemical conditions or distinct kinds of combinations1 one of which readily gives up its constituents to growing plants1 while the other does not2 and the constituents have1 therefore1 been called respectively 8available0 and 8non-available40 ,it would appear from his writings that ,liebig regarded this distinction as applying to the 8absorbed0 or 8adsorbed0 mineral matter2 that is1 on the one hand the material held in or upon the soil grains by surface forces1 and on the other the chemically combined constituents in the minerals themselves4 ,we know that ,liebig was much impressed by the absorption experiments of ,way1 and himself did much work in this field4#i ,but the great body of soil investigators has evidently held to the opinion that there are two general classes of minerals in the soil4 ,some have held that the 8available0 potassium is held in zeolites or 8zeolitic0 minerals1 an interesting example often cited being glauconite or 8green sand marl10 which sometimes contains phosphorus as well as potassium2#aj in minerals which are easily broken down by alkaline solutions1 as by sodium carbonate solutions or ammonia2 or in minerals which are easily broken down by organic acids supposedly excreted from the roots of growing plants1 or formed by the decay of plant tissue4#aa #i ,way was misled1 as we now know1 in considering the results of his absorption experiments with soils as merely metathetical reactions2 see ,absorption by soils1 by ,harrison ,e4 ,patten and ,william ,h4 ,waggaman1 ,bull4 ,no4 #eb1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijh4 #aj ,the formation of zeolites in the soil has often been assumed1 but has not yet been proven2 see ,rocks1 rock-weathering and soils1 by ,george ,p4 ,merrill1 #aijf1 p4 #cfc4 #aa ,the classic experiments of ,sachs1 in producing etchings on marble slabs1 and the etchings observed occasionally on rock surfaces are the proofs universally cited4 ,the experiments of ,czapek1 who substituted slabs of aluminum phosphate and other substances for the marble1 and those of ,kossowitch1 show that the action can be accounted for more satisfactorily and reasonably as due to dissolved carbon dioxide4 ,in fact such etchings can be produced on marble slabs by laying platinum wires upon them and covering with moist soil1 or cotton1 or mats of filter-paper2 see ,bull4 ,no4 #bb1 p4 #ad1 and ,bull4 ,no4 #cj1 p4 #da1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture4 ,with the advent of this idea of a distinction between the available and non-available mineral plant-food elements in the soil1 came attempts to distinguish them by analytical methods4 ,of these attempts we now have a bewildering array1 most of them frankly empirical4 ,for instance1 ,hilgard1 in his classical investigation of the cotton soils for the ,tenth ,census1 treated his soil samples with an excess of hydrochloric acid1 evaporated to dryness1 extracted with water1 and regarded the extracted mineral constituents as available4 ,in ,germany1 a method similar to ,hilgard's is now in common use1 while in ,france nitric acid is preferred generally because it is supposed to have peculiar solvent powers on soil phosphates4 ,in the ,united ,states the 8official method0 of the ,association of ,official ,agricultural ,chemists is to keep #aj grams of the soil in contact with #ajj cc4 of a solution of hydrochloric acid 7specific gravity #a4aae7 at the boiling point of water for exactly #aj hours4 ,in ,england the popular method is that proposed by ,dyer1 namely1 to treat the soil with a #a per cent4 citric acid solution1 this strength of solution being supposed at one time to represent the average acidity of root sap4 ,maxwell1 in ,hawaii1 and afterwards in ,australia1 claimed good results for the extraction of the soil with a #a per cent4 solution of aspartic acid1 this acid being employed on the erroneous ground that the organic acids of the soil are amino acids1 and that these are the effective agents in dissolving the soil minerals and rendering their constituents 8available40 ,the ,kentucky ,agricultural ,experiment ,station favors an ,n_/#e nitric acid solution1#ab but does not recommend its use for soils of other localities1 while in a contiguous state1 the ,tennessee ,station favors the 8official0 method4#ac ,many other methods have been proposed1 but the foregoing are typical and sufficient to illustrate the present status of soil analysis4 #ab ,soils1 by ,a4 ,m4 ,peter and ,s4 ,d4 ,averitt1 ,bull4 ,no4 #abf1 p4 #ff1 7#aijf74 #ac ,the soils of ,tennessee1 by ,charles ,a4 ,mooers1 ,bull4 ,no4 #gh1 p4 #di1 7#aijf74 ,it is clear that these several methods must give differing results4 ,and it is not clear that any one of them is to be preferred to the others for any reasons than analytical convenience4 ,there is no reason to expect that the proportion of solvent to soil required in these methods bears any relation whatever to the mechanism of absorption by plant roots4 ,and the attempts to simulate the properties of plant sap in some of these solvents are obviously illogical1 for the plant sap does not come in contact with the soil grains1 except through an accidental destruction of the plant4 ,naturally1 comparisons were attempted between the amounts of the mineral constituents extracted from a soil by these various solvents and the amounts taken up by crops growing on the soil4 ,it was found1 however1 that the amount of any given mineral constituent extracted from the soil by a solvent is not1 generally1 the same as that taken up by the plant4 ,moreover1 the ratio of one constituent to another in the extract bears no definite relation to the ratio of these constituents in the plant4 ,nevertheless many efforts were made to establish 8factors40 ,for instance1 the percentage of potash extracted from the soil of a field by hydrochloric acid is some multiple of the percentage removed by a wheat crop2 it was sought to determine this multiple1 assuming it to be a definite ratio and a natural constant1 and it was designated as the potash factor4 ,but there is a different factor for phosphorus1 another for calcium1 and still others for each and every constituent4 ,the factors found for a soil from one area generally do not hold for a soil from another area4 ,again1 different factors obviously must be used for different crops4 ,and1 finally1 the whole scheme becomes hopeless when it is realized that the same crop will yield widely varying ash analyses1 depending upon the cultural methods employed1 the judicious selection of seed1 the amount and distribution of rainfall and sunlight1 and possibly other agencies1 all of which affect the growth and absorptive functions of the plant to as great an extent as does the particular soil upon which it may be growing4 ,moreover1 from the purely analytical point of view the situation is no better4 ,for instance1 the addition of potassium in the amounts usually employed in ordinary fertilizer practice generally does produce a noticeable effect on the yield of crop4 ,the average application of potash 7,k,o7 is certainly less than #ej lbs4 to the acre4 ,it is customary to consider the surface foot of soil as the region affected by the fertilizer1 and an acre foot in good moisture condition weighs about #d1jjj1jjj lbs4 ,to be conservative1 let it be assumed that #fj lbs4 of potash have been added to #c1jjj1jjj lbs4 of soil4 ,the official method of the ,association of ,official ,agricultural ,chemists calls for the determination of the potash in #b grams of soil1 which on the basis of the present assumption calls for the estimation of an added amount of #j4jjjjd gram of potash or #j4jjb per cent4 ,taking as an example the report of the ,association of ,official ,agricultural ,chemists for #ahiead there are given the following results obtained independently by a number of analysts1 on soils which had presumably been sampled by the referee with all possible care3 #ad ,proceedings of the ,twelfth ,annual ,convention of the ,association of ,official ,agricultural ,chemists1 ,bull4 ,no4 #dg1 ,division of ,chemistry1 ,u4 ,s4 ,dept4 ,agriculture1 p4 #cf1 7#ahif74 ,,potash ,,calculated ,,as ,,per ,,cent4 ,,of ,,the ,,fine ,,dried ,,earth4 #a #b #c #d ,analyst ---------------------------------------- ----- ,per ,per ,per ,per cent4 ,var4cent4 ,var4cent4 ,var4cent4 ,var4 ---------------------------------------- ------------- ,a #j4cei #j4jddj4aed-j4jjb -- -- -- -- ,b #j4cde #j4jcjj4aab-j4jddj4chjj4jeaj4ajd-j4jej ,c #j4ced #j4jcij4bce #j4jgij4cifj4jfgj4bbe #j4jga ,d #j4bfj-j4jee -- -- -- -- -- -- ,e #j4cgc #j4jehj4agi #j4jbcj4cfej4jcfj4age #j4jba ,f #j4baj-j4ajej4acj-j4jbfj4bbjj4ajij4aji-j 4jde ,g #j4cjd-j4jaaj4abe-j4jcaj4bhfj4jdcj4aeh #j4jjd ,mean #j4cae -- #j4aef -- #j4cbi -- #j4aed -- ---------------------------------------- ------------- ,not only do the individual determinations show differences far in excess of #j4jjb per cent41 but the differences between each individual reading and the mean is greater than #j4jjb per cent41 so that it is evident from these results that the analytical procedure fails to recognize appreciable amounts of the so-called available plant foods4 ,consequently the 8acid digestion0 of a soil fails of the purpose for which it was designed1 and it is one of the mysteries of chemical history that so much time and energy have been devoted to such a hopeless quest4 ,this state of affairs is the more surprising when the limitations of the analytical procedure are considered4 ,the data tabulated above indicate that the analyses were made with an exactness that justifies a statement to three decimal places1 that is1 to three significant figures2 and in fact1 as was shown1 such is necessary if the figures are to have any significance regarding fertilizer applications4 ,it is obvious that the analysis of a finely pulverized definite mineral or rock is less subject to error than a sample of soil sifted through a #b mm4 mesh4 ,yet the ,u4 ,s4 ,geological ,survey commonly reports its analytical data to only hundredths of a per cent41 that is1 to two decimal places4 ,what variation may be expected in duplicate determinations by the same analysts it is difficult to say1 for such duplicates are not commonly published4#ae ,in spite of the widespread view that the chemical analysis of a soil is a statement of great accuracy1 it is improbable that as usually determined the potash content is correct to three or even two significant figures2 it is also doubtful if the phosphoric acid content is correct to even one significant figure1 if the total amount is below #j4a per cent4 of the soil4 ,that these determinations have a higher accuracy than here stated is not shown by an inspection of the literature including the fairly numerous results reported in the annual ,proceedings of the ,association of ,official ,agricultural ,chemists4 #ae ,see3 ,on the interpretation of mineral analyses1 by ,s4 ,l4 ,penfield1 ,amer4 ,jour4 ,sci41 7#d71 #aj1 #cc1 7#aijj72 ,the analysis of silicate and carbonate rocks1 by ,w4 ,f4 ,hillebrand1 ,bull4 ,no4 #cje4 ,u4 ,s4 ,geol4 ,surv41 #aijg2 ,manual of the chemical analysis of rocks1 by ,h4 ,s4 ,washington1 #aijd1 p4 #bd2 ber ,genauigkeit von ,gesteinanalysen1 von ,m4 ,dittrich1 ,neues ,jahrbuch fr ,mineralogie und ,palaeontologie1 #b1 #fi1 7#aijc74 ,it was early felt by some investigators that soil analyses were unsatisfactory for studying the relation of the soil to the food requirements of a crop1 and a second method was devised1 namely1 the growing of a crop1 and determining the amount of mineral constituents removed from the soil by analyzing the ash of the crop4 ,from the point of view of practical soil management this procedure involves the serious difficulty of being first obliged to get the crop before determining what must be done to best get it4 ,it apparently has the scientific advantage of directness in determining the mineral needs of the plant from the plant itself4 ,if these needs were constant1 the advantage would be real1 but as already mentioned1 one and the same plant may have a very different ash content as the result of different cultural methods1 different climatic and seasonal factors1 as well as different soils4 ,generally1 a poor crop has a higher percentage of ash content than a good crop1 and sometimes the poor crop may remove from the soil more in absolute amounts of some one or other of the ash constituents than does the good crop4 ,the ratio of the ash constituents is by no means constant for any one crop1 and of course varies with different crops4#af ,finally1 it is now known that the amount of the several mineral nutrients which a soil must furnish to a crop in the earlier stages of growth is greater than the crop contents at maturity1#ag consequently an analysis of the ripe crop would not indicate the plant's drain upon the soil at all growing periods4 ,so that1 while ash analyses have taught some important things concerning plant growth1 they have of necessity failed as guides or criteria of the crop-producing power of a soil1 its fertilizer requirements1 or its content of 8available0 plant-food4 #af ,for a brief but comprehensive discussion of ash analyses see1 ,the ash constituents of plants1 etc41 by ,b4 ,tollens1 ,expt4 ,sta4 ,rec41 #ac1 #bjg-bbj1 #cje-cag1 7#aija-jb74 #ag ber die ,nhrstoffaufnahme der ,pflanzen in verschiedenen ,zeiten ihres ,wachstums1 von ,wilfarth1 ,rmer und ,wimmer4 ,landw4 ,vers4 ,sta41 #fc1 #a-gj1 7#aije72 ,plant food removed from growing plants by rain or dew1 by ,j4 ,a4 ,le ,clerc and ,j4 ,f4 ,breazeale1 ,year ,book1 ,u4 ,s4 ,dept4 ,agriculture1 #aijh1 p4 #chi-djb4 ,a third method of soil investigation1 also essentially analytical in character1 is the plot or pot test4 ,the difference between a plot or pot experiment is mainly one of size1 although it is claimed1 and with a certain amount of justice1 that the plot experiment more nearly approximates actual practice1 and should be given a somewhat different consideration than the more readily controlled pot experiment4 ,here again it has to be considered that seasonal factors and factors other than the soil play a relatively large part in the production of the crop1 so that conclusions regarding the productivity of a soil can not be drawn from one season's crop4 ,also1 nowadays it is recognized generally that continuous growing of one crop is an incorrect practice1 and a rotation should be followed and repeated several times before conclusions regarding the productivity of the soil are justified4 ,if1 however1 the rotation has been well managed1 the cultivation1 fertilizing and soil management generally been well done for sixteen1 twenty or more years1 the soil has materially changed1 and there can be no assurance that the treatment then best for it1 is that which was best at the beginning of the experiment4 ,therefore the method throws no certain light on the productive power of the soil1 or the availability of its mineral plant-food constituents4 ,although much has been learned from plot experiments1 and especially from the better controlled pot experiments1 they are inadequate to meet the fundamental problem of the relation of the chemical characteristics of the soil to its crop-producing powers4 ,chapter ,,iv4 ,,the ,,plant-,,food ,,theory ,,of ,,fertilizers4 ,the guiding principle in soil investigations for about three-quarters of a century and until the past few years has been the assumption that the principal function of the soil is to furnish mineral nutrients to the plant1 and that1 to supply a lack in the soil1 fertilizers are added because of the mineral plant nutrients they contain4 ,this theory has apparently much to support it2 actually1 however1 the evidence usually cited accords better with a more comprehensive generalization which will be formulated in a later chapter4 ,it is attractively simple4 ,it will be shown later1 however1 that this very simplicity is an argument against its validity4 ,those substances which experience has shown to be useful soil amendments usually contain one or more of the constituents necessary to plant metabolism1 commonly phosphorus1 potassium1 nitrogen or calcium4 ,fertilizers do not always produce increased yields of crops1 but it has been usual to consider bad results as due to other more or less extraneous causes4 ,moreover1 as will appear later1 crop yield is as strongly affected by some substances containing no mineral plant nutrient as by ordinary fertilizers4 ,again1 the plant-food theory has been apparently confirmed by the popular misconception that crop yields are decreasing4 ,government statistics1 however1 indicate very positively that crop yields are increasing in ,europe as well as in ,america1 more in areas where the acreage is stationary than in areas where the acreage is increasing1 and in areas where fertilizers are not used as well as in areas where they are used4 ,analyses of ,european soils which have been cropped for centuries show no characteristic differences from the newer soils of the ,united ,states4#ah ,it is true that1 from bad management or other causes1 individual fields where crop production has fallen off are not uncommon4 ,but that such a condition is general or that it can be associated generally with a decreased content in the soil of any particular mineral substance or substances1 is a conclusion not sustained by the available data4 #ah ,a study of crop yields and soil composition in relation to soil productivity1 by ,milton ,whitney1 ,bull4 ,no4 #eg1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aiji4 ,the plant-food theory of fertilizers must now be regarded as entirely insufficient4 ,granting that it has been useful in the past and has occasioned much valuable work1 it seems to have reached the point which another simple and temporarily useful theory1 the phlogiston theory of combustion1 reached shortly before the plant-food theory of fertilizers was evolved4 ,just as the phlogiston theory passed away when the elementary nature of oxygen was established and ,lavoisier taught the scientific world to use the balance1 so the plant-food theory of fertilizers must pass with increasing knowledge of the relation of soil to plant and the application of modern methods of research to the problem4 ,chapter ,v4 ,,the ,,dynamic ,,nature ,,of ,,soil ,,phenomena4 ,in soil investigations1 until recently1 the assumption has been made1 more or less explicitly1 that any given soil mass1 as for instance a field1 remains fixed or in place indefinitely4 ,it has been admitted1 of course1 that some physical1 chemical and biological processes might be taking place in the soil1 but these have been regarded as relatively unimportant in their effects upon the soil mass in toto4 ,it has been assumed that the only important change taking place in the soil is a loss of mineral plant nutrients1 partly by leaching1 partly by removal in the garnered crops4 ,in other words1 the soil has been regarded as a static system4 ,this is a fundamental error4 ,in studying the soil as a medium for crop production1 we must consider the plant itself1 or at least that part of the plant which enters the soil1 namely1 the root2 the solid particles of the soil2 the soil water1 or the aqueous solution from which the plant draws all the materials for its sustenance1 excepting the carbon dioxide absorbed by its aerial portions2 the soil atmosphere2 the biological processes taking place4 ,the one common characteristic of all these things is that they are continually in a state of change2 therefore the soil problem is essentially dynamic4 ,the root of a growing plant is always moving4#ai ,the amount of motion may be small or large1 depending upon the surrounding conditions or attendant circumstances1 but cessation of motion means the death of the root4 ,this becomes evident from a consideration of the mechanism of root growth4 ,the living root absorbs and excretes water and dissolved substances through a restricted area just back of the root tip or the tips of the root hairs4 ,while absorption is taking place1 however1 there is a deposition of denser material over the absorbing area1 or 8root corking40 ,but coincident with the corking process1 the tip is pushed forward between the soil grains into the nutrient medium1 new cells are formed and a new absorbing surface continually brought into functional activity4 ,a failure of the plant root to move forward in this way would mean a reabsorption of root effluvia with harmful consequences to the plant1 or a corking over of the root without further formation of absorbing surface and with consequent cessation of its functioning4 ,this would mean the inevitable death of the root1 and1 if general1 of the whole plant4 ,it is clear1 therefore1 that root penetration and absorption of plant nutrients are essentially dynamic4 #ai ,in order to penetrate the soil1 a living root must be capable of exerting large pressures1 and indeed1 the magnitude of these pressures has been determined for some cases4 ,see1 for citations of the literature1 ,pfeffer1 ,plant ,physiology1 translated by ,ewart1 #aijc1 ,vol4 #b1 p4 #abd et seq4 ,but it can not be doubted that1 in general1 root movement is much facilitated and perhaps directed by movements among the soil particles4 ,as the absorbing tip of the root removes film water from the adjacent soil grains1 there is a necessary rearrangement of these grains with a shrinking away from the tip1 which then moves forward by taking advantage of the movements among the soil grains4 ,the solid components of the soil are always in motion4 ,every soil1 no matter how flat the area or how well protected by vegetal covering1 suffers some translocation of soil material through rains1 as is evidenced by suspended material in the run-off waters4 ,on hillsides this is shown by the soil accumulating on the 8up0 sides of fences1 especially stone fences4 ,in the aggregate this movement is probably quite large everywhere4 ,it is manifestly so in the watersheds of many of the world's important rivers as shown by their muddy waters and the formation of deltas1 sometimes of great area and agricultural importance4 ,with the saturation or approach to saturation of the surface soil the particles are more easily moved among themselves by an extraneous force4 ,it is very rarely that the surface of a field is a dead level4 ,consequently when the soil is wetted1 the gravitational force on the individual soil grains produces a more or less pronounced 8creeping0 effect down hill4 ,on decided slopes this soil creep is believed to be of great importance in connection with soil erosion4#bj ,as important as is the translocation of material by water1 quite as important probably is that produced by the winds4 ,these are blowing all the time1 uphill as well as down1 and their range of action is thus far wider than is that of rain and flood4 ,the effectiveness of the wind as a translocating agency is seldom realized or even suspected by the layman1 although it is commonly known that the air always contains some dust1 and dust storms are familiar phenomena4 ,that soil material can be carried long distances is certain1 however1 as for instance the sirocco dust1 often carried from the ,sahara over ,europe4#ba ,dust carried high into the air by volcanic eruptions sometimes travels enormous distances1 as in the case of the eruption of ,krakatoa1 when such material is reported to have traveled thousands of miles1 and volcanic debris from the eruptions at ,soufrire fell upon ships several hundred miles distant4 ,arctic explorers have reported the finding of wind-borne soil materials over the polar ice1 and mountaineers have observed similar deposits on snow-capped peaks4 ,soil material on roofs and similar inaccessible places has been observed many times1 and testifies to the continual activity of the wind4 ,the burial of objects even of considerable size by wind-borne soil gives like testimony4 #bj ,soil erosion is undoubtedly one of the greatest economic problems of the time1 and yet there is scarcely any subject about which there are current so many popular misconceptions4 ,in the rivers and to those who use the rivers the water-borne soil material is an unmitigated nuisance1 save possibly to a few cultivators of low-lying lands who for one reason or another1 may flood their fields for the sake of the silt deposited4 ,to the upland farmer1 however1 erosion is not only a necessity of natural conditions which can not be avoided entirely1 but under proper control it may be even a blessing4 ,the scalded and gullied hillsides1 a trial and unnecessary disgrace to the owner1 are probably not the main sources of the material which finds its way to the river4 ,on the contrary1 what are regarded usually as well-tilled fields supply the greater part of the suspended material in the rivers4 ,the problem of erosion on the farm is not merely to check gullying and scalding1 and deepening of stream heads1 but to so adjust both cropping system and cultural methods as to secure a reasonable translocation of surface soil material with a minimum contamination of the neighborhood streams4 ,see1 ,man and the earth1 by ,nathaniel ,southgate ,shaler1 #aije4 #ba ,for a comprehensive discussion of wind as a translocating agent1 see3 ,the movement of soil material by the wind1 by ,e4 ,e4 ,free1 ,bureau of ,soils1 ,bull4 ,no4 #fh1 ,u4 ,s4 ,dept4 ,agriculture4 ,measurements of the amount of action of wind in translocating soil material are rare and probably have a qualitative value only4 ,but ,udden#bb in what appears to be a conservative calculation1 finds 8the capacity of the atmosphere over the ,mississippi ,valley to transport dust is #ajjj times as great as that of the ,mississippi ,river40 ,the wind seldom is carrying anything like so great a load as it is capable of carrying4 ,that is1 the wind in its attack upon the land surface does not ordinarily obtain so large an amount of material capable of being wind-borne as it is possible for the wind to carry when suitable material is artificially provided4 ,it should be remembered that1 speaking generally1 the velocity of the wind is lower just at the surface of the ground than at heights above1 and it is necessary to get the soil material above the surface before the wind can exercise its full efficiency as a carrying agent4 #bb ,erosion1 transportation and sedimentation performed by the atmosphere1 by ,j4 ,a4 ,udden1 ,jour4 ,geol41 #b1 #cah-cca 7#ahid74 ,moreover1 wind-borne material is constantly being deposited as well as being removed from the land surface4 ,it is evident1 however1 that this movement of soil material by winds is very great1 and there is no reason to believe that it is of any less importance in other areas than in the ,mississippi ,valley4 ,it is also evident that the individual grains in any surface soil of any particular field or area are continually and more or less rapidly changing1 and the farmer is not dealing to-day with just the same soil complex he faced a few years back1 or will face a few years hence4 ,but besides the movements of the solid components of the soil by translocating agencies1 other movements are constantly taking place4 ,whenever a moderately dry soil becomes wetted1 it 8swells up0 until a certain critical amount of moisture is present above which there is a shrinking4 ,but as a wet soil dries out again below the critical amount1 there is again a shrinking4 ,as it is always either raining or not raining1 soils are always either getting wetted or are drying4 ,consequently the individual grains are continually moving about among themselves4 ,a heavy object1 such as stone1 when left on the ground gradually sinks into it4#bc ,earthworms1 burrowing animals and insects are continually at work in most arable soils4 ,the action of frost in 8heaving0 a soil is familiar to everyone4 ,not so well known1 however1 is the fact that the apparently superficial cracks which occur to a greater or less extent in every soil1 under drought conditions1 are in reality quite deep1 extending well into the subsoil4 ,by the edges breaking off1 and by wind- and water-borne material being carried in1 considerable surface soil is thus brought into the subsoil4 ,through these various agencies1 therefore1 the solid components of the soil are continually subject to much mixing2 subsoil is becoming surface soil1 and to some extent vice versa4 ,an important result of these various processes is the bringing into the surface soil of degradation and decomposition products from underlying rocks4 ,the processes involved are essentially dynamic4#bd #bc ,on the small vertical movements of a stone laid on the surface of the ground1 by ,horace ,darwin1 ,proceedings of the ,royal ,society of ,london1 #fh1 #bec-bfa1 7#aija74 ,on the other hand1 geological literature would probably furnish numerous references to the heaving out of boulders1 probably as the result of successive freezings and thawings of the soil4 ,the shape of the stone as well as the specific nature of the movements of the soil particles evidently has an important influence in determining whether the stone sinks into the soil or vice versa4 #bd ,it is clear that as the soil is continually changing through physical agencies1 the chemical analysis of it can not be expected to furnish evidence as to the mineral constituents removed by crops or by leaching4 ,the soil solution is also a dynamic problem4 ,when the rain falls on the soil1 a part1 the 8run-off10 flows over the surface and finds its way into the regional drainage2 a part immediately evaporates into the air1 and is designated as the 8fly-off20 a third part1 the 8cut-off10 enters the soil4#be ,the cut-off water penetrates the soil by way of the larger openings and interstices1 and mainly under the influence of gravity4 ,for convenience this downward-moving water is designated as 8gravitational0 water4 ,it moves through the soil with comparative rapidity and a portion reappears elsewhere as seepage water1 springs1 etc4 ,but with the return of fair-weather conditions at the surface1 there is increased evaporation and augmentation of the fly-off1 and there is developed a drag or 8capillary pull0 on the water below4 ,a large portion of the cut-off thus returns to the surface1 mainly through films over the surface of the soil grains and in the finest interstices4#bf #be ,this terminology has been suggested by ,dr4 ,w4 ,j4 ,mc,gee4 #bf ,leather1 however1 thinks the water returns from only a limited depth1 some #e-g feet2 see1 ,the loss of water from soil during dry weather1 by ,j4 ,walter ,leather1 ,memoirs of the ,department of ,agriculture1 ,agricultural ,research ,institute1 ,pusa1 ,india1 ,chemical series1 ,i1 #gi-aaf1 7#aijh74 ,dr4 ,george ,n4 ,coffey has called the author's attention to some observations in ,western ,kansas1 where a prolonged drought had dried the soil to a considerable depth4 ,a fairly heavy rain wetted the soil to less than two feet from the surface1 and practically all of this moisture had returned to the surface and evaporated within a few days4 ,such special cases as these1 however interesting in themselves1 are even less so than the normal cases in humid areas1 where a part of the water passes through the soil as seepage1 the larger portion returning to the surface1 sometimes through distances of many feet4 ,the soil atmosphere is continually in motion1 following with more or less decided lag the barometric changes in the atmosphere above the soil4 ,moreover1 the chemical and physical processes continually taking place in the soil involve the absorption or the formation of free carbonic acid1 and it seems probable that all rain water penetrating the soil gives up some oxygen to the soil atmosphere4 ,the bacteria and lower life forms are necessarily undergoing changes continually4 ,in fact all components of the soil are continually undergoing1 or are involved in1 changes of one kind or another4 ,it is certain that investigation of the various motions and changes taking place in the soil is quite as important as investigation of the soil components1 and that no clear idea of the chemistry of the soil can be obtained without it4 ,the development of a rational practice of soil control is possible only when the soil is regarded from a dynamic viewpoint4 ,chapter ,,vi4 ,,the ,,film ,,water4 ,when a relatively small quantity of water is added to an absolutely dry soil or other powdered solid1 there is some shrinkage in the apparent volume of the soil or powder4 ,the water spreads over the surfaces of the solid particles in a film1 and a rise in temperature shows that a noticeable energy change accompanies the formation of the film4#bg ,with further increments of water the apparent volume of the soil increases until a maximum is reached4 ,the water content at which this maximum volume of soil can be attained is a definite physical characteristic for any given soil4 ,what is popularly known as the 8optimum water content0 corresponds to this critical content4#bh ,it is the point at which further additions of water will not increase the thickness of the moisture film on the soil grains1 but will give free water in the soil interstices4 ,just as the apparent volume of a given mass of soil varies with the water content1 and reaches a maximum at a critical moisture content1 so do all the physical properties vary and have either a maximum or minimum value at this same critical moisture content4 ,thus the apparent specific gravity of a soil reaches a minimum1 the force required to insert a penetrating tool becomes a minimum1 while the rate at which a soil warms up reaches a maximum1#bi and the ease with which aeration takes place reaches a maximum4 ,in fine1 this critical water content is that at which the soil can be brought into the best possible physical condition for the growth of crops4 ,the practical significance of the optimum water content is far greater than would be supposed from the attention given it hitherto by students of the soil4 ,it is the content of soil water which the greenhouse man should strive to maintain1 and which the irrigation farmer should seek to provide1 instead of the over-wetting so common to the practice of both4 ,in general farming it is that moisture content at which the farmer will attain the best results in plowing and cultivating1 and attain these results most readily4 #bg ,see1 in this connection1 ,energy changes accompanying absorption1 by ,harrison ,e4 ,patten1 ,trans4 ,am4 ,electrochem4 ,soc41 #aa1 #chg-djg1 7#aijg72 see also the recent valuable research1 ,les dgagements de chaleur qui se produisent an contact de la terre sche et de l'eau1 par ,a4 ,muntz et ,h4 ,gaudechon1 ,ann4 sci4 agron4 7#c71 #d1 ,,ii1 #cic-ddc1 7#aiji71 where it is shown that probably a part of the heat is due to chemical combination between the water and the other soil components4 ,to quote1 8,ces diverses observations nous conduisent penser1 sans nous en donner toutefois la preuve absolute1 que la fixation de l'eau sur les lments terreux trs fins et sur les matriaux organiss1 est tout au moins1 en partie1 attribuable une combinaison chimique qui se manifeste non seulement par un fort dgagement de chaleur1 mais aussi par la soustraction de l'eau des substances aux-quelles elle semble chimiquement lie40 #bh ,the moisture content and physical condition of soils1 by ,frank ,k4 ,cameron and ,francis ,e4 ,gallagher1 ,bull4 ,no4 #ej1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 of ,agriculture1 #aijh4 ,see also ber physikalische ,bodenuntersuchung1 von ,h4 ,rodewald1 ,schriften ,naturwiss4 ,vereins ,schleswig-,holstein1 #ad1 #cig-cii1 7#aiji74 #bi ,heat transference in soils1 by ,harrison ,e4 ,patten1 ,bull4 ,no4 #ei1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aiji4 ,with additions of water beyond the critical point1 there is a presence of free water in the soil interstices accompanied by important changes in the soil structure4 ,with continued additions1 there is a more or less rapid decrease in the apparent volume2 there is a tendency for the soil aggregates to break down and the 8crumb structure0 so greatly desired by agriculturists is less and less readily obtained1 and working of the soil tends in some cases to produce that phenomenon known as 8puddling40 ,however desirable the property of puddling may be to the potter or the brick maker1 to the farmer it is a bane to be avoided above all things4 ,to overcome it requires his best skill1 and it usually takes several years of patient effort to restore a puddled soil to good tilth4 ,the force with which the film water is held against the soil grains has not been determined as yet with any degree of precision1 but it is certainly very great4 ,if a soil be saturated1 that is1 if so much water be added that further additions will cause a flow of free water1 and the soil be then submitted to some mechanical device for abstracting the water1 the moisture content of the soil can be readily diminished to the critical water content2 but to diminish it further by mechanical means is not easy4 ,the tenacity with which film water is held by the soil grains has been shown in several ways4 ,in one of these1 for instance1 a semi-permeable membrane was precipitated in the walls of a porous clay cell1 which was then filled with sugar solution having an osmotic pressure of about #ce atmospheres4 ,when this cell was buried in a soil having a moisture content above the optimum1 water flowed into the cell4 ,on the contrary1 when the cell was buried in another sample of the same soil having a moisture content well below the optimum1 there was a marked flow of water from the cell4 ,it would appear1 therefore1 that the attraction between the soil grains and the film-forming water was certainly greater than the solution pressure of the sugar4#cj ,again1 by whirling wetted soils in a rapidly revolving centrifuge1#ca fitted with a filtering device in the periphery1 and developing a force equivalent on the average to #c1jjj times the attraction of gravitation1 the soils could not be reduced below the critical water content4 ,from the results of ,lagergren1#cb ,young1#cc and ,lord ,rayleigh1#cd it appears that the force holding a very thin moisture film on the soil grains would be of an order of magnitude from #f1jjj to #be1jjj atmospheres4 ,this force1 however1 must greatly decrease with thickening of the film1 as is shown by the fact that at the critical moisture content a small further addition of water produces no marked heat manifestation1 though making a noticeable difference in the physical properties of the soil4 ,therefore1 while recognizing that our knowledge of this force still lacks a desirable precision1 it is nevertheless clear that the force is very great4 #cj ,the chemistry of the soil as related to crop production1 by ,milton ,whitney and ,frank ,k4 ,cameron1 ,bull4 ,no4 #bb1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijc1 p4 #ed4 #ca ,the moisture equivalent of soils1 by ,lyman ,j4 ,briggs and ,john ,w4 ,mc,lane1 ,bull4 ,no4 #de1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijg4 #cb ber die beim ,benetzen fein verteilter ,krper auftretende ,wrmetnung1 von ,lagergren1 ,bihang till ,k4 sv4 ,vet4-,akad41 ,handl41 #bd1 ,afd4 ,,ii1 ,no4 #e1 7#ahih74 #cc ,hydrostatics and elementary hydrokinetics1 ,george ,m4 ,minchin1 p4 #caa1 #ahib4 #cd ,on the theory of surface forces1 by ,lord ,rayleigh1 ,phil4 ,mag4 7#e71 #cj1 #bhe-bih1 #def-dge1 7#ahij74 ,the function of the film water in maintaining the soil structure is undoubtedly important4 ,a soil in good tilth1 or good condition for crop growth1 shows a peculiar structural arrangement of the individual soil grains or soil particles1 which it is very difficult to describe in precise terms1 but which is readily recognized in practice4 ,this condition is usually described as a 8crumb structure10 either because of its appearance or because of the peculiar crumbly feeling which a soil in this condition gives when rubbed between the fingers4 ,the individual grains of soil are gathered into groups or floccules4 ,while other causes may be more or less operative in particular cases1 it seems very probable that the film water is primarily the agency holding together the grains in these floccules4 ,the obvious explanation is that the film is exerting a holding power because of its surface tension4 ,it follows1 therefore1 that anything which affects the surface tension of water should affect the structure of the soil2 that is1 the flocculation or granulation of the particles4 ,but certain agents which produce respectively flocculation or deflocculation1 nevertheless modify the surface tension of the solution in the same direction1 and in not widely varying degree4 ,similar difficulties arise in attempting to correlate 8crumbing0 phenomena with the viscosity of the film water1#ce and it must be admitted frankly that present views on this subject are very unsatisfactory1 and that more careful investigation is urgently needed on this fundamental and important problem4 ,not only is the absence of a satisfactory theory embarrassing in considering the problems of soil structure and a rational control1 but the difficulties are no less in the equally important problems of the movement of film moisture1 and the distribution of moisture in a soil4 #ce ,equally unsuccessful is the attempt to correlate flocculating agents with changes in the density of water4 ,see1 ,the condensation of water by electrolytes1 by ,f4 ,k4 ,cameron and ,w4 ,o4 ,robinson1 ,jour4 ,phys4 ,chem41 #ad1 #a-aa1 7#aiaj74 ,the movement of moisture into a soil from an illimitable supply is a comparatively simple phenomenon1 controlled by a rate law which may be expressed by the equation y kt when y is the distance through which the movement has taken place2 t is the time1 and k and n are characteristic constants for the particular soil and solution4#cf ,this expression may be more readily recognized as a rate formula when written dy_/at ,ay1 where ,a and m are constants for the particular system4 ,the first form of the equation promises to be the more useful4 ,this formula also describes the rate of advance of a dissolved substance into the soil4 ,owing to irregularities in the soil column this equation is more readily studied with capillary tubes or with such absorbents as filter-paper or blotting paper4 ,the following tables will1 however1 give an idea as to its validity for soils4 ,,alluvial ,,soil1 ,,gila ,,river4#cg ,time1t min4 ,height1y inches k 7n #a4hf7 ---------------------------------------- ------------ #b #a4e #a4je #e #b4d #a4jb #aj #c4f #a4jh #ae #d4c #a4ja #cj #f4c #a4je #fj #i4b #a4jg ---------------------------------------- ------------ ,,distilled ,,water ,,in ,,penn4 ,,loam 7t #ba ,c74 ,time1t ,height1y k min4 cm4 7n #b4be7 ---------------------------------------- #a #a4ae #a4cg #b #a4ed #a4cc #c #a4he #a4cc #d #b4jh #a4cj #e #b4bh #a4bh #g #b4ei #a4ba #aj #b4ig #a4af #ae #c4dg #a4aj #bj #c4ij #a4jg #cj #d4fg #a4jf #dj #e4ci #a4aa #ej #e4ij #a4ji #fj #f4dg #a4ab #ge #g4bj #a4ac #ij #h4jc #a4ba #aje #h4gb #a4be ---------------------------------------- #cf ,see ,bull4 ,no4 #cj1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 p4 #ej et seq42 also1 ,the flow of liquids through capillary spaces1 by ,j4 ,m4 ,bell and ,f4 ,k4 ,cameron1 ,jour4 ,phys4 ,chem41 #aj1 #fei1 7#aijf72 ,see also1 ,wo4 ,ostwald1 #b ,supplementheft ,zeitschrift ,kolloidchemie1 #aijh1 #bj4 #cg ,computed from observations by ,loughridge1 ,report ,agr4 ,expt4 ,sta41 ,university ,california1 #ahic-id1 p4 #ic4 ,,indigo ,,carmine ,,in ,,penn4 ,,loam ,,soil 7t #ba ,c474 ,solution contained #b grains dye per liter4 ,time1t ,height1y k for water ,height colored k for dye min4 wet cm4 7n #b4be7 cm4 7n #b4be7 ---------------------------------------- ------------------------ #a #a4bh #a4ge #j4fd #j4cg #b #a4fg #a4ei #j4ij #j4ci #c #b4je #a4fh 44 44 #d #b4bf #a4ef 44 44 #e #b4di #a4ef #a4jb #j4ba #g #b4gd #a4ch 44 44 #aj #c4bj #a4dj 44 44 #ae #c4gb #a4bi 44 44 #bj #d4bh #a4cb #a4ib #j4bb #cj #e4aj #a4ca 44 44 #dj #e4gg #a4bi #b4fi #j4bc #ej #f4da #a4bf #c4bj #j4bh #fj #f4ij #a4bi 44 44 #ge #g4df #a4bc 44 44 #ij #h4gd #a4df #c4ei #j4bj #aje #i4jj #a4cc 44 44 ---------------------------------------- ------------------------ ,it has also been shown repeatedly by experiment that the movement of moisture is relatively rapid when the moisture content of the soil is above the optimum1 but that the movement is exceedingly slow when the soil has a lower water content than the optimum2 that is1 the point at which the water is entirely in the form of film water4 ,for instance1 if a moderately wet sample of soil be brought into intimate contact with an air-dry sample of the same soil1 there will1 at first1 be a relatively rapid movement of the moisture1 but as soon as the wetted portion has been brought to the 8optimum0 condition1 no further movement can be detected1 although the experiment has been tried of leaving such samples together for months and with a difference of water content amounting1 in the case of clay soils1 to #ae or #bj per cent4 ,since the drought limit1 or the soil moisture content at which plants wilt1 is1 for most soils1 considerably below the optimum water content1 the movement of film water is obviously a problem of the first importance from a practical point of view as well as of the highest theoretical interest4 ,the movement of water vapor1 or its distillation from place to place in the soil1 is another problem often confused with the above4 ,its importance is not yet clear1 although according to some investigators#ch it would appear that the addition of soluble fertilizer salts by causing a lowering of the vapor pressure of the water induces a distillation to that region from other regions of the soil as well as from the atmosphere above4 ,this brings up the problem of the diffusion of water and other vapors through the soil4 ,it has been shown that the soil 8plug0 retards the rate at which diffusion takes place but induces no other effect in the ordinary phenomenon of free diffusion4 ,this fact is obviously of the first importance in the theory of mulches1 but requires no further consideration here4#ci #ch ,sur la diffusion des engrais salins dans le terre1 par ,muntz et ,gaudechon1 ,comptes rendus1 #adh1 #bec-beh1 7#aiji74 #ci ,see1 ,contribution to our knowledge of the aeration of soils1 and ,studies of the movement of soil moisture1 by ,edgar ,buckingham1 ,bulls4 ,nos4 #be1 #aijd1 and #cc1 #aijg1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 of ,agriculture4 ,chapter ,,vii4 ,,the ,,mineral ,,constituents ,,of ,,the ,,soil ,,solution4#dj ,the mineral constituents of the soil are products of the disintegration1 degradation and decomposition of rocks4 ,the decomposition products are mainly silica in the form of quartz1 ferruginous material consisting of more or less hydrated ferric oxide and alumina1 and hydrated aluminum silicate4 ,the ferruginous material1 being deposited or formed in the soil in a very finely divided condition1 frequently coats the soil fragments to such an extent as completely to mask their true character4 ,but if a soil be thoroughly shaken with water1 and especially in the presence of some deflocculating agent such as a slight excess of ammonia1 as in the ordinary preparation of a soil sample for mechanical analysis#da the coating material is generally removed quite readily1 and the mineral particles appear as fragments and splinters of the ordinary rock-forming minerals4 ,sometimes these fragments are more or less worn and rounded at the edges1 showing mechanical abrasion or solvent action2 sometimes they show evidences of partial alteration and decomposition2 but surfaces of the unaltered mineral individuals always are found4 ,these unaltered minerals occur as fragments of all sizes1 and are to be found in the sands1 silts1 and presumably in the clays4 ,as might be anticipated1 the minerals other than quartz generally show a tendency to segregate in the finer mechanical separations of the soil4 ,the presence of these unaltered mineral fragments in the clays has so far defied direct experimental proof because of the limitations of the microscope1 but from chemical reasoning and a priori considerations there can be but little doubt that they exist in the clays as in the coarser separations4#db #dj ,for a more detailed discussion and citations of the literature1 see ,the mineral constituents of the soil solution1 by ,frank ,k4 ,cameron and ,james ,m4 ,bell1 ,bull4 ,no4 #cj1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aije4 #da ,centrifugal methods of mechanical soil analysis1 by ,l4 ,j4 ,briggs1 ,f4 ,o4 ,martin and ,j4 ,r4 ,pearce1 ,bull4 ,no4 #bd1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijd4 #db ,see1 ,the mineral composition of soil particles1 by ,g4 ,h4 ,failyer1 ,j4 ,g4 ,smith and ,h4 ,r4 ,wade1 ,bull4 ,no4 #ed1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aiji4 ,recent improvements in microscope methods make it possible to identify without serious trouble the mineral content of silts with a diameter as low as #j4jje mm41 and many even of the clay particles have recently been determined with satisfactory accuracy4 ,the minerals to be anticipated in the soil are those commonly occurring in the rocks2 but as a result of the action of mixing and transporting agencies1 a soil normally contains minerals from rocks other than those from which it is primarily derived4 ,it would hardly be fair to regard a beach sand1 for instance1 as a normal soil4 ,yet it is surprising how many minerals other than quartz can usually be found even in a beach sand4 ,opinions may differ as to just what are the common rock-forming minerals1 and perhaps no two mineralogists or petrographers would give identical lists1 but there are a number of minerals which would appear undoubtedly in every list1 and these would be found generally in any soil4 ,again1 it might happen that in any given sample of soil1 no pyroxene1 for instance1 could be found2 but experience shows that it would never happen in such a case that no amphibole1 chlorite1 serpentine1 or other ferro-magnesian silicates would be present4 ,however distinct these minerals cited may be from each other morphologically or optically1 they are much the same in their chemical characteristics1 their solubilities and their reactions with water and such dilute solutions as exist in the soil4 ,hence from the point of view of the soil chemist they may be considered for all practical purposes varieties of one and the same mineral species4 ,consequently an important result of researches on the minerals of the soil is the generalization that soils are far more heterogeneous than are rocks1 and that practically every soil contains all the common rock-forming minerals4#dc #dc ,see ,bull4 ,no4 #cj1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aije1 p4 #i4 ,it is not difficult to account for the heterogeneity of the mineral content of the soil4 ,many of our rocks are reconsolidated soils1 and the alternating formation of rock and soil from the same materials is probably an agency1 in some part at least1 in the mixing of soil material4 ,the action of water in carrying off and transporting surface material and in gullying and eroding sloping surfaces is probably a large factor4 ,but this agency1 like the first1 is rather restricted and localized4 ,just as important as a mixing agency is the wind4 ,this1 unlike water1 works uphill as well as down1 and is more or less in action at all times1 continually transporting soil material from place to place4 ,wind-borne dust on roofs of dwellings1 on rocky mountain tops and similar places1 where it could have been brought by no other agency than the wind1 is sometimes found supporting vegetation4 ,many chemical and mineralogical analyses of wind-borne dust obtained from various locations show it to have generally the same essential characteristics as ordinary soils4 ,aside from the quartz and ferruginous materials mentioned above1 the major part of the soil minerals are silicates1 ferro-silicates1 alumino-silicates1 or ferro-alumino-silicates1 of the common bases1 sodium1 potassium1 calcium1 magnesium1 and ferrous iron4 ,other bases1 such as lithium1 barium1 or the heavy metals may occasionally be present in appreciable amounts as may other types of silicates1 or other mineral salts1 but these may be regarded as more or less incidental and rarely affecting in any essential way the general character of the soil mass4 ,these silicates or silico minerals are all somewhat soluble in water1 and being salts of weak acids with strong bases1 are greatly hydrolyzed4 ,a convenient illustration is afforded by the well-known rock and soil mineral1 orthoclase4 ,assuming its type formula1 the reaction with water may be represented1 ,k4,al,si,o ,,hoh ,h4,al,si,o ,,koh4 ,under ordinary soil conditions1 with a relatively large proportion of carbon dioxide in the soil atmosphere1 the potash formed would be more or less completely transformed to the bicarbonate1 ,,koh ,,co ,h,o ,,khco ,h,o4 ,confirmation of this view is afforded by the natural associations and known alteration products of orthoclase4 ,the acid of the formula ,h4,al,si,o is not known and is probably entirely instable under ordinary conditions1 and breaks down with the separation of silica1 to form the minerals pyrophyllite1 kaolinite or kaolin1 and diaspore according to the following equations3 ,h4,al,si,o - ,si,o ,h4,al,si,o 7,pyrophyllite7 ,h4,al,si,o - #b,si,o ,h4,al,si,o 7,kaolinite7 ,h4,al,si,o - #c,si,o ,h4,al,o 7,diaspore74 ,all three of these minerals and their corresponding salts have been found in nature as alteration products of orthoclase4 ,it is probable that1 under soil conditions1 the principal metamorphic product of feldspar is kaolin 7or kaolinite when it is crystalline71 hydrated aluminum oxide being of much less importance#dd and pyrophyllite of doubtful occurrence4 ,a still more interesting case1 perhaps1 because of the well recognized tendency of magnesium salts to form basic compounds1 is the alteration of pyroxene1 amphibole and olivine with the formation of a chlorite or serpentine1 common associations in nature1 which may be represented #dd ,see ,ueber die ,bildung von ,bauxit und verwandte ,mineralien1 von ,a4 ,liebrich1 ,zeit4 prakt4 ,geol41 #ahig1 #bab-bad4 ,mg,si,o ,,hoh ,mg,si,o4n,mg7,,oh7 ,si,o4 ,it is tacitly assumed in the foregoing statements that the reaction between a silicate mineral and water is a reversible reaction4 ,this is not definitely known to be the case1 for the formation of the ordinary silicate rock-forming minerals in the wet way at ordinary temperatures has as yet been realized in only a few cases4 ,the assumption has1 however1 some experimental support4 ,minerals have been often made in the wet way at somewhat elevated temperatures1 especially interesting cases in this connection being the formation of orthoclase by ,friedel and ,sarasin#de at slightly elevated temperatures1 and the formation of zeolites by ,gonnard#df and by ,doroshevskii and ,bardt1#dg and the formation of apatite by ,weinschenk4#dh ,feldspars and zeolites are common natural associations1 it being generally conceded that zeolites are alteration products of the feldspars through the action of water2 but ,van ,hise#di has pointed out that under conditions of weathering such as would obtain in the soil1 the tendency is for the zeolites to alter to feldspars4 ,whler's classical experiment of recrystallizing apophyllite from hot water#ej is significant1 for only the products of hydrolysis should be obtained if there is an irreversible reaction between the mineral and water4 ,lemberg found that leucite 7,k,al,si,o7 when treated with an aqueous solution containing #aj per cent4 or more of sodium chloride1 was partially transformed to analcite 7,na,al,si,o4n,h,o71 potassium chloride being formed at the same time4 ,the reverse reaction was also realized1 that is1 the partial conversion of analcite to leucite by treatment with a solution of potassium chloride1 and similar transformations were carried out with the feldspars4#ea ,lemberg's experiments are of especial value as they were carried out at ordinary as well as at high temperatures4 ,it appears probable1 therefore1 that the hydrolysis of a silicate of the alkalis or alkaline earths is a reversible reaction4 ,it should be noted1 however1 that ,kahlenberg and ,lincoln#eb have shown that probably1 in very dilute solutions of alkali silicates1 the hydrolysis is practically complete and the silica is nearly all present as colloidal silica and not as silicic acid4 ,nevertheless at higher concentrations silicates are formed1 and there is abundant evidence in nature that the alumino- or ferro-silicates are reacting with bases to form salts1 for example such as the micas4#ec ,if the hydrolysis were quite complete1 it would appear to follow that the reaction between water and the silicate is irreversible4 ,in that case it is difficult to see how any silicate mineral could persist in the soil for any length of time1 and all soils should soon become sterile wastes composed essentially of quartz1 kaolin and ferruginous oxides4 ,it has been suggested that the original mineral particles are protected from decomposition by the formation of a coating 8gel40 ,that is1 that silica1 alumina1 ferruginous or other materials result from the decomposition of the minerals in a jelly-like form on the surface of the soil grains1 protecting them from further action of the soil solution4#ed ,if diffusion can take place through the gel1 solution and hydrolysis of the mineral would proceed1 although the presence of the gel would probably retard the rate of the reaction4 ,if it be postulated1 however1 that diffusion through the gel does not take place1 the minerals of the soil can have no influence on the composition of the soil solution1 which is an unthinkable alternative4 ,the presence of such gels in the soil has frequently been assumed1 but satisfactory proof is generally wanting4 #de ,sur la reproduction par voie aqueuse du feldspath orthose1 par ,friedel et ,sarasin1 ,comptes rendus1 #ib1 #acgd1 7#ahha74 #df ,note sur une observation de ,fournet1 concernant la production des zolites a froid1 par ,f4 ,gonnard1 ,bull4 ,soc4 min4 ,france1 #e1 #bfg-bfi1 7#ahhb72 ,jahrb4 ,min41 #ahhd4 ,i1 ,ref4 #bh4 #dg ,metathetical reactions with artificial zeolites1 by ,a4 ,doroshevskii and ,a4 ,bardt1 ,jour4 ,russ4 ,phys4 ,chem4 ,soc41 #db1 #dce-db 7#aiaj74 ,chem4 ,zentr41 #aiaj1 ,,ii1 #fh4 #dh ,beitrge zur ,mineralsynthesis1 von ,e4 ,weinschenk1 ,zeit4 ,kryst41 #ag1 #dhi-ejd1 7#ahij74 #di ,u4 ,s4 ,geol4 ,surv4 ,monograph1 #dg1 ,a treatise on metamorphism1 by ,charles ,r4 ,van ,hise1 #aijd1 p4 #ccc4 #ej ,jahresb4 ,fortschr4 ,chemie ,liebig and ,kopp1 #ahdg-dh1 #abfb2 note4 #ea ,ueber ,silicatumwandlungen1 von ,j4 ,lemberg1 ,zeit4 deutsch4 geol4 ,ges41 #bh1 #eai-fba1 7#ahgf72 ,inaug4 diss4 ,dorpat1 #ahgg2 ,bied4 ,centbl41 #h1 #efg-egg1 7#ahgi74 #eb ,solutions of silicates of the alkalis1 by ,l4 ,khlenberg and ,a4 ,t4 ,lincoln1 ,jour4 ,phys4 ,chem41 #b1 #gg-ij1 7#ahih74 #ec ,van ,hise1 loc4 cit41 p4 #fic4 #ed ,a gel is a jelly-like substance1 apparently continuous1 which forms either by the settling from suspension in a liquid of very fine particles which then become aggregated2 or1 is formed by the evaporation of a liquid containing fine particles in suspension until the quantity of liquid remaining is just sufficient to serve as a cementation medium holding the suspended particles together in a semi-rigid mass4 ,for an experimental demonstration of the formation of such a gel1 see1 ,the effect of water on rock powders1 by ,allerton ,s4 ,cushman1 ,bull4 ,no4 #ib1 ,bureau of ,chemistry1 ,u4 ,s4 ,dept4 ,agriculture1 #aije4 ,in general1 the same kind of considerations developed for orthoclase hold for the other soil minerals4 ,if minerals of this character be pulverized or ground reasonably fine and then be shaken with distilled water which has been previously boiled to eliminate the dissolved carbon dioxide1 the resulting solution will give an alkaline reaction with such indicators as phenolphthalein or litmus4#ee ,if a soil be shaken up thoroughly with water1 the resulting solution filtered free of suspended matter1 as by passing through a ,pasteur-,chamberland bougie1 and then boiled to eliminate the carbon dioxide1 in the vast majority of cases the solution will also give an alkaline reaction with phenolphthalein or litmus4 ,the waters of most of our springs1 ponds1 creeks or rivers being natural soil solutions1 give an alkaline reaction after boiling4 #ee ,in making such experiments in the laboratory or in lecture demonstrations1 it is well to have the mass of water large in comparison with the mass of powdered mineral or rock2 otherwise secondary adsorption effects may occur and obscure the results of the hydrolysis4 ,but the mineral content of these natural waters varies greatly4 ,these waters are composed in part of the 8run-off10 in part of a portion of the 8cut-off0 waters1 described above4 ,this portion of the cut-off1 normally1 in passing through the soil goes mainly through the larger interstices4 ,it is not long in contact with the individual soil particles and floccules1 and because diffusion of dissolved mineral substances is quite slow1 especially in dilute solutions1 it takes up but little mineral matter from such aqueous films as it may intercept4 ,a different state of things exists with that portion of the cut-off water which returns towards the surface by reason of capillary forces1 to form the great natural nutrient medium for plants4 ,this water is moving over the soil particles in films1 and with slowness4 ,it is long in contact with successive fragments of any particular mineral and all the different minerals making up the soil4 ,consequently1 it tends towards a saturated solution with respect to the mineral mass2 and it follows that if every soil contains all the common rock-forming minerals1 every soil should give the same saturated solution1 barring the presence of disturbing factors4#ef ,disturbing factors1 however1 enter into all cases under field conditions1 such for instance as the presence of some uncommon or unusual mineral in appreciable amounts1 differences in temperature1 surface effects1 or extraneous substances4 ,these will be considered later1 but another disturbing factor requires immediate consideration4 ,in every soil1 varying proportions of the soluble mineral constituents are present otherwise than as definite mineral species2 that is1 they are present as solid solutions1 or absorbed on the soil grains or perhaps absorbed in some other manner4 ,the concentration of the liquid solution in contact with a solid solution or complex of absorbent and absorbed material is dependent upon the relative masses of solution and solid4 ,thus1 the concentration of a solution with respect to phosphoric acid1 when brought into contact with so-called basic phosphates of lime or iron1 is dependent in a marked way upon the proportion of solution to solid4#eg ,consequently it is to be expected that an aqueous extract of a soil will vary in concentration with the proportion of water used2 and that with the same proportion of water1 different soils or different samples of the same soil will yield different concentrations4 #ef ,feldspars certainly1 and phosphorites possibly1 are mineral components of the soil2 and these substances when ground sufficiently fine have been added to soils with sometimes an increased production of crop4 ,other minerals1 such as leucite1 have given similar results4 ,but also apparently pure quartz sand sometimes accomplishes the same results1 as for example1 in the experiments of ,hilgard cited above4 ,it has not been shown1 however1 that the addition of any of these substances produces an appreciable change in the concentration of the soil solution4 #eg ,the action of water and aqueous solutions upon soil phosphates1 by ,frank ,k4 ,cameron and ,james ,m4 ,bell1 ,bull4 ,no4 #da1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 of ,agriculture1 #aijg4 ,how far absorbed mineral constituents affect the solubility of the definite minerals in the soil or influence the concentration of the soil solution1 it is not possible to predict with any approach to certainty4 ,those soils which hold the most moisture are generally the best absorbers4 ,moreover1 the soluble mineral constituents of the soil1 for instance potassium or phosphoric acid1 are absorbed to a very high degree from dilute solutions4 ,consequently it is to be expected that variations in the concentration of the natural soil solution would be less than in aqueous extracts1 when there is employed a constant and relatively large proportion of water to soil4 ,these considerations are of great theoretical importance since they appear to negative the possibility of getting1 with present experimental resources1 any exact knowledge of the concentrations of the mineral constituents in the soil solution when the soil is in condition to grow the common crop plants4 ,moreover1 they furnish a guide to the limitations which must be recognized in attempting to postulate what these concentrations may be on the basis of analytical data obtained from aqueous soil extracts4 ,many attempts have been made to extract the solution naturally existing in the soil and to analyze it4 ,the results obtained have not been very satisfactory1 owing mainly to the mechanical difficulties involved4 ,as pointed out above1 the solution in a soil under suitable conditions for crop growth is held by a force of great magnitude4 ,nevertheless1 by using powerful centrifuges1 with saturated soil1 it has been possible to throw out the excess of solution over the critical water content of the soil4 ,in this way small quantities1 generally a very few cubic centimeters at a time1 have been obtained4 ,the analysis of a few cubic centimeters of a very dilute solution is in itself difficult1 involving necessarily more or less uncertainty as to the absolute value of the results4 ,nevertheless1 the concentration of the soil solutions thus obtained1 with respect to phosphoric acid and potash1 varied but little for soils of various textures from sands to clays1 and the variations observed could not be correlated with the known crop-producing power of the soils4 ,the average concentrations of the soil solutions thus obtained lies in the neighborhood of #f-h parts per million 7p4p4m47 of solution for phosphoric acid 7,p,o7 and #be-cj parts per million for potash 7,k,o74#eh ,in the following table are given the results obtained by analyzing solutions extracted from different samples of loams and sands by means of a centrifuge4 ,the crop growing on these soils and the crop condition at the time the samples were collected are given in the table1 and the percentages of water in the samples when placed in the centrifuge are also given4 #eh ,in this connection it is interesting to note that recent investigations on the proportions of phosphoric acid1 potassium and nitrates in cultural solutions best adapted to the growth of wheat1 give the same ratio of phosphoric acid to potassium as the figures just cited show to exist normally in the soil solution4 ,,analysis ,,of ,,soil ,,solution ,,removed ,,from ,,fresh ,,soils ,,by ,,the ,,centrifuge4 ,parts per million of solution ,soil ,crop ,condition,per cent ---------------- of crop moisture4 ,,po ,ca ,k ---------------------------------------- -------------------- ,leonardtown loam ,wheat ,good #bb4j #f #ag #bb ,leonardtown loam ,wheat ,poor #be4b #aj #i #ai ,leonardtown loam ,wheat ,good #ag4f #h #bb #ch ,sassafras loam ,clover ,good #ai4g #e #ah #ai ,sassafras loam ,corn ,medium #ag4e #h #ac #cf ,sassafras loam ,corn ,medium #ah4c #h #hc #be ,sassafras loam ,wheat ,good #ah4h #g #dd #cd ,sassafras loam ,wheat ,poor #bj4j #g #bg #bd ,sassafras loam ,corn ,good #ag4c #h #bd #be ,norfolk sand ,forest ,poor #aj4j #e #ah #ca ,norfolk sand ,corn ,good #aa4i #aa #cf #ca ,norfolk sand ,wheat ,good #aj4g #ah #de #ca ,norfolk sand ,wheat ,poor #aa4b #h #ch #bd ,norfolk sand ,corn ,medium #aj4f #i #fe #ce ---------------------------------------- -------------------- ,the concentrations of the solutions obtained from the samples do not justify any correlation with the crop-producing power of the soils1 nor with the texture of the soils4 ,the wide variation in the concentrations with respect to calcium is probably due to the fact that all of the samples came from fields which had been limed1 some quite recently1 and that the content of carbon dioxide in the different samples varied4 ,it is of special interest to note that the content of calcium in the solutions does not show any obvious relation to the content of phosphoric acid4#ei #ei ,for the literature of the earlier work on the composition of aqueous extracts of soils1 see3 ,how crops feed1 by ,samuel ,w4 ,johnson1 #ahij1 p4 #cji et seq42 see also4 ,on the analytical determination of probably available 8mineral0 plant-food in soils1 by ,bernard ,dyer1 ,jour4 ,chem4 ,soc4 #fe1 #aae-afg1 7#ahid72 and ,soils1 by ,e4 ,w4 ,hilgard1 #aijf1 p4 #cbg et seq4 ,an effort has been made to ascertain the mineral concentration of soil solutions as they occur naturally in the field4 ,because of the practical impossibility of extracting the actual soil solution1 an empirical method was employed4 ,areas were selected where good and poor crops were growing near each other on the same soil types1 and preferably in the same field4 ,samples of soil from under these crops were taken at several intervals during the growing season1 quickly removed to a nearby laboratory1 shaken thoroughly with distilled water in the proportion of one part of soil to five parts of water1 allowed to stand twenty minutes and the supernatant solution passed through a ,pasteur-,chamberland filter4#fj #fj ,capillary studies and filtration of clays from soil solutions1 by ,lyman ,j4 ,briggs and ,macy ,h4 ,lapham1 ,bull4 ,no4 #ai1 ,bureau of ,soils4 ,u4 ,s4 ,dept4 ,agriculture1 #aijb2 ,colorimetric1 turbidity and titration methods used in soil investigations1 by ,oswald ,schreiner and ,george ,h4 ,failyer1 ,bull4 ,no4 #ca1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijf4 ,as has been pointed out above1 the aqueous extract of a soil thus arbitrarily prepared has no definite or causal relation to the soil solution in the field4 ,it is certain that the solutions would not generally be the same4 ,it should also be emphasized that such a procedure can not1 as some investigators have assumed1 afford a criterion between soluble and insoluble salts in the soil1 else the proportion of water to soil used above some minimum would be immaterial as far as the amounts which go into solution are concerned4 ,the proportion of water to soil is not immaterial1 however1 considering the chemical nature of the soil components and the results of experiment4 ,consequently1 it is clear that the concentration of the soil solution is not simply the ratio of the amounts found in the aqueous extract1 to the percentage of moisture in the soil1 but something quite different4 ,artificial solutions prepared in the manner described above should1 however1 furnish evidence as to whether or not there are recognizable differences in the soluble mineral constituents of good and poor soils respectively2 and if such differences exist1 whether they are consistent4 ,that is to say1 if the more productive soils also uniformly yield aqueous extracts of a higher concentration1 then it would be a fair inference that their natural soil solutions are maintained at a higher concentration than in the less productive soils4 ,results obtained for several localities and several crops1 taken from the original records1 are given in the following tables4#fa #fa ,the chemistry of the soil as related to crop production1 by ,milton ,whitney and ,f4 ,k4 ,cameron1 ,bull4 ,no4 #bb1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijc4 ,,water ,,soluble ,,constituents ,,of ,,soil4 ,locality1 ,salem1 ,n4 ,j4 ,soil type1 ,norfolk sand4 ,crop1 wheat4 ,yield1 good4 ,parts per million of oven-dried soil ,depth ,moisture ------------------------------------- ,date inches content ,phosphoric ,calcium ,potassium ,per cent4 acid 7,,po7 7,ca7 7,k7 ---------------------------------------- ----------------------- ,march #aj #j-ab #ac4b #ab #e #ab #ab-bd #aa4e #g #e #af ,june #h #a-bd #d4c #d #ad #ac ,june #ac #a-bd #d4f #e #ac #ag ,june #ai #a-bd #i4f #b #ad #bd ---------------------------------------- ----------------------- ,locality1 ,salem1 ,n4 ,j4 ,soil type1 ,norfolk sand4 ,crop1 wheat4 ,yield1 poor4 ,parts per million of oven-dried soil ,depth ,moisture ------------------------------------- ,date inches content ,phosphoric ,calcium ,potassium ,per cent4 acid 7,,po7 7,ca7 7,k7 ---------------------------------------- ----------------------- ,april #c #j-ab #ab4j #aa #e #cb #ab-bd #ab4j #aj #c #bb ,june #af #a-bd #i4c #d #bi #bj ---------------------------------------- ----------------------- ,locality1 ,salem1 ,n4 ,j4 ,soil type1 ,sassafras loam4 ,crop1 wheat4 ,yield1 medium4 ,parts per million of oven-dried soil ,depth ,moisture ------------------------------------- ,date inches content ,phosphoric ,calcium ,potassium per cent4 acid 7,,po7 7,ca7 7,k7 ---------------------------------------- ----------------------- ,march #aj #j-ab #bc4b #ai #aj #h #ab-bd #ba4f #aa #aj #ad ,march #ad #j-ab #bb4c #ah #h #ah #ab-bd #bj4b #ae #ab #ba #bd-cf #bj4c #ah #ag #af ,march #bj #j-ab #ai4c #g #aj #ba #ab-bd #ah4f #d #aa #ba #bd-cf #ab4f #e #ab #ba ,june #af #a-bd #bb4e #d #ad #bc ---------------------------------------- ----------------------- ,locality1 ,salem1 ,n4 ,j4 ,soil type1 ,sassafras loam4 ,crop1 grass4 ,yield1 fair4 ,parts per million of oven-dried soil ,depth ,moisture ------------------------------------- ,date inches content ,phosphoric ,calcium ,potassium ,per cent4 acid 7,,po7 7,ca7 7,k7 ---------------------------------------- ----------------------- ,march #aj #j-ab #be4j #ac #bh #ah #ab-bd #bc4h #g #bf #ac #bd-cf #ai4i #af #h #ae ,march #ad #j-ab #be4h #ba #ab #ba #ab-bd #bc4a #h #ab #ae #bd-cf #ba4h #i #ae #ba ,march #ca #j-ab #bc4j #aa #bc #dc #ab-bd #ba4f #h #bj #cd ,april #b #j-ab #bd4h #h #af #da #ab-bd #bd4j #f #ba #ch #bd-cf #ba4d #c #aa #be ---------------------------------------- ----------------------- ,locality1 ,salem1 ,n4 ,j4 ,soil type1 ,sassafras loam4 ,crop1 wheat4 ,yield1 good4 ,parts per million of oven-dried soil ,depth ,moisture ------------------------------------- ,date inches content ,phosphoric ,calcium ,potassium per cent4 acid 7,,po 7,ca7 7,k7 ---------------------------------------- ----------------------- ,march #ag #j-ab #bb4j #h #f #aj #ab-bd #ah4a #h #ae #ad ,march #ag #j-ab #ah4c #aj #ae ,lost #ab-bd #ah4a #i #bd #be ,march #bd #j-ab #bd4g #ad #ab #cj #ab-bd #bb4c #h #aa #ch ,march #bf #j-ab #bc4d #d #af #af #ab-bd #bc4i #ab #af #bj #bd-cf #bb4d #h #c #ba ,april #b #j-ab #be4f #h #af #cj #ab-bd #bd4d #h #ag #dg #bd-cf #ba4f #h #aa #ch ,june #e #j-ab #e4b #ad #ea #bc #ab-bd #h4j #ae #ee #cb ,june #h #a-bd #aj4f #b #bj #ac ,june #aa #a-bd #ae4e #f #bf #ad ,june #ac #a-bd #h4b #f #ai #bb ,june #af #a-bd #ae4j #e #ba #ai ,june #ag #a-bd #aj4f #g #fc #ag ---------------------------------------- ----------------------- ,locality1 ,salem1 ,n4 ,j4 ,soil type1 ,sassafras loam4 ,crop1 clover4 ,yield1 fair4 ,parts per million of oven-dried soil ,depth ,moisture ------------------------------------- ,date inches content ,phosphoric ,calcium ,potassium per cent4 acid 7,,po7 7,ca7 7,k7 ---------------------------------------- ----------------------- ,march #bj #j-ab #bj4h #e #ae #cb #ab-bd #bj4b #e #ae #bg #bd-cf #ah4f #e #ab #cf ,march #bf #j-ab #bf4h #i #ca #bj #ab-bd #bb4i #h #bj #ah #bd-cf #bb4e #d #ad #bj ,june #f #j-ab #h4a #h #af #ag #ab-bd #ab4g #i #ah #bj ---------------------------------------- ----------------------- ,locality1 ,st4 ,marys1 ,md4 ,soil type1 ,leonardtown loam4 ,crop1 wheat4 ,yield1 good4 ,parts per million of oven-dried soil ,depth ,moisture ------------------------------------- ,date inches content ,phosphoric ,calcium ,potassium per cent4 acid 7,,po7 7,ca7 7,k7 ---------------------------------------- ----------------------- ,april #bg #j-ab #ba4h #e #aj #ab #ab-bd #ba4c #d #g #aj ,april #bi #j-ab #bb4b #h #ae #eb #ab-bd #ba4h #d #aa #ch ,may #a #j-ab #bb4d #g #ad #bc #ab-bd #ba4h #g #h #cj ,may #a #j-ab #ag4j #e #af #be #ab-bd #ba4j #e #g #ai ,may #i #j-ab #ae4j #ac #cd #bh #ab-bd #ae4i #i #ag #bf ,may #ae #j-ab #ad4b #c #ad #bd #ab-bd #ai4i #d #ac #be ,august #ad #j-bd #ae4j #f #aa #ac ,august #ae #j-bd #ae4g #e #c #ag ,august #ae #j-bd #af4d #h #ae #ae ---------------------------------------- ----------------------- ,locality1 ,st4 ,marys1 ,md4 ,soil type1 ,leonardtown loam4 ,crop1 wheat4 ,yield1 poor4 ,parts per million of oven-dried soil ,depth ,moisture ------------------------------------- ,date inches content ,phosphoric ,calcium ,potassium per cent4 acid 7,,po7 7,ca7 7,k7 ---------------------------------------- ----------------------- ,may #ad #j-ab #ad4g #e #h #ce #ab-bd #ai4i #d #d #cj ,may #bc #j-ab #g4h #d #g #bb #ab-bd #ad4i #d #aa #bc ,august #ad #j-bd #af4j #d #d #af ,august #ae #j-bd #ai4e #f #d #ac ---------------------------------------- ----------------------- ,locality1 ,st4 ,marys1 ,md4 ,soil type1 ,leonardtown loam4 ,crop1 corn4 ,yield1 good4 ,parts per million of oven-dried soil ,depth ,moisture ------------------------------------- ,date inches content ,phosphoric ,calcium ,potassium per cent4 acid 7,,po7 7,ca7 7,k7 ---------------------------------------- ----------------------- ,may #h #j-ab #ah4b #i #ab #bi #ab-bd #ah4i #aj #g #bf ,may #ah #j-ab #ah4b #c #bd #ch #ab-bd #ah4h #f #ai #bh ,august #h #j-bd #ag4e #g #cj #ah ---------------------------------------- ----------------------- ,locality1 ,st4 ,marys1 ,md4 ,soil type1 ,leonardtown loam4 ,crop1 corn4 ,yield1 poor4 ,parts per million of oven-dried soil ,depth ,moisture ------------------------------------- ,date inches content ,phosphoric ,calcium ,potassium per cent4 acid 7,,po7 7,ca7 7,k7 ---------------------------------------- ----------------------- ,may #bc #j-ab #af4f #e #ab #bb #ab-bd #ag4d #f #h #bb ,august #h #j-bd #ai4i #i #be #bj ,august #ae #j-bd #ba4f #g #ae #ac ---------------------------------------- ----------------------- ,it will be observed that the results given in the above tables are expressed in parts per million of oven-dried soils1 in order to have some definite basis of comparison1 and because it was anticipated at the time the investigation was made that larger quantities of dissolved minerals would be found under the better crops1 and vice versa4 ,an inspection of the results1 however1 shows that no such correlation can be made1 nor in fact can any consistent correlation be made between the dissolved material and crop1 soil type1 water content1 depth of soil or part of the growing season4#fb ,it appears1 therefore1 that in so far as the field method of analyzing an arbitrarily prepared aqueous extract is competent1 there is no evidence that there are important characteristic differences in the concentration of the mineral constituents in different soil solutions in the field4 #fb ,king1 however1 claims that the concentration of the soil solution with respect to mineral plant nutrients1 is higher in the soils of the northern states than in the soils of the ,south ,atlantic states4 ,see3 ,some results of investigations in soil management1 by ,f4 ,h4 ,king1 ,yearbook1 ,u4 ,s4 ,dept4 ,agriculture1 #aijc1 p4 #aei-agd4 ,bailey ,e4 ,brown has obtained some preliminary results which suggest that there may be seasonal variations with respect to some of the dissolved mineral constituents4 ,see1 ,annual ,report of the ,pennsylvania ,state ,experiment ,station1 #aijh-i1 pp4 #ca et seq4 ,the order of concentration of the soil solution can be approximated from the given data1 if the assumption be made that in the preparation of the aqueous extract1 soluble mineral constituents are of minor importance1 other than the constituents already dissolved in the soil solution4 ,the calculation is very laborious1 is not exact1 and on account of the assumptions made the actual figures obtained are of no especial value in any particular case4 ,remembering the method of making up the solutions from which these results were obtained1 it would be sufficiently near the truth to assume an average moisture content of #bj per cent41 when the figures given here for the soil approximate those which would be obtained for the soil solution4 ,more exact calculations have been made for a large number of such cases1 and it has been found from this method of estimation that the average composition with respect to phosphoric acid would be about #f-h parts per million1 and for potash about #be parts per million1 figures which agree with the results obtained for the examination of solutions extracted from saturated soils by means of the centrifuge4 ,the results given in the foregoing tables were obtained under great difficulties1 and in some part the variations they show are undoubtedly due to inevitable inaccuracies of analytical work done under such circumstances4 ,some of the variations may also be due to the disturbing influences in the soil referred to above4 ,experience has shown1 however1 that the preparation of an aqueous extract of the soil of any particular field is by no means a simple matter4 ,extracts made from samples taken within a few feet of one another frequently show variations of the same order as with samples from entirely different fields1 or even soil types4 ,differences in the preliminary drying out of the sample before the addition of the water1 seems to result in the same order of differences as obtained between different soils4 ,in consequence of these facts1 and of the further fact that an arbitrary aqueous extract of a soil cannot be assumed to represent in any definite way the natural soil solution1 the results of the field examination are inconclusive as to the concentration of the soil solution in situ4 ,it is more necessary1 therefore1 that other lines of evidence should be sought as to the mineral characteristics and concentration of the soil solution4 ,such a line of evidence is found in certain percolation experiments4#fc #fc ,the absorption of phosphates and potassium by soils1 by ,oswald ,schreiner and ,george ,h4 ,failyer1 ,bull4 ,no4 #cb1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijf4 ,if a solution of a soluble phosphate be percolated through a soil1 a part of the phosphate will be removed from the solution and absorbed by the soil2 that is1 there will be a redistribution of the phosphate between the soil and the water4 ,as the process continues1 however1 relatively less and less phosphate is absorbed by the soil and the concentration of the percolate becomes more and more nearly that of the added solution4 ,this absorption takes place more or less closely in accordance with the simple law that the absorption of phosphates by the soil1 per unit of solution which is percolating1 is proportional to the total amount of phosphate which the soil may yet take from that solution if percolated indefinitely4 ,this law is expressed by the equation dy ------------ ,k7,a - y7 dx where y is the amount absorbed1 x amount of solution that has passed1 and ,a is the total amount which can ultimately be absorbed by that particular soil from that particular solution4 ,k is also a characteristic constant4 ,if the percolation be maintained at constant rate1 then t1 time1 can be substituted for x and the equation becomes dy -------- ,k7,a - y71 dt the ordinary rate equation for a mono-molecular reaction of the first order1 whether chemical or physical4 ,with such absorptions as are involved in soils1 a clay exposes a greater amount of absorbing surface than does a loam or sand1 and it will show the greatest absorption towards any particular solution1 other things being equal4 ,the curve showing the concentration of percolate would lie lower for a clay than for a loam1 or for a sand4 ,this is illustrated in the accompanying sketch diagram1 where y represents concentration of percolate and t represents time4 ,illustration3 ,fig4 #a4 ,if after percolation has proceeded for some time 7in some experiments for several weeks and until the soil contained #a or #b per cent4 of phosphoric acid7 pure water be passed through the soil1 then1 as soon as the previously used phosphate solution has been displaced1 the concentration of the percolate drops and continues practically constant for an indefinite period4 ,moreover1 no matter what the soil may be as to texture or composition1 the same concentration of percolate is obtained1 namely1 #f-h parts per million1 the concentration which the soils yielded prior to treatment with the phosphate solution4 ,similar experiments when the soils were treated with salts of potassium have given like results1 although the curves obtained from passing pure water through the soils do not lie quite so close together2 but the concentration of the percolate with respect to potassium generally lies somewhere between #be and #cj parts per million4 ,the removal of a soluble constituent from the soil by percolating water appears to be described by a rate equation similar to that given above for absorption4 ,if the rate of percolation be maintained constant this formula is dx ---------- ,k7,b - x7 dt where x is the amount removed by the percolation1 with time t1 ,k is a constant characteristic for the particular system under consideration1 and ,b is the total amount of the constituent which may ultimately be leached out4 ,in other words1 the rate in any particular soil will depend upon the amount of the constituent still absorbed in that soil but has no necessary connection with the rate which would hold for the same amount of the constituent in any other soil4 ,theoretically1 two consequences follow from this law which require consideration here4 ,the rate at which a constituent is removed gradually becomes less as percolation proceeds4 ,if the soil contains an amount of the constituent approaching the total amount which it can absorb1 as for instance is probably the case sometimes when large applications of lime have been made to the soil1 the concentration of the percolating solution might be expected to change noticeably4 ,generally1 however1 a soil contains nowhere near as much phosphoric acid or potassium as it is capable of absorbing1 so that the concentration of the percolating water changes but very little with respect to these constituents4 ,it follows from the equation that if percolation continues uninterrupted1 the concentration of the percolate1 so far as it is determined by an absorbed constituent1 must get less and less until it becomes a vanishing quantity4 ,this state of affairs does not exist in the soil1 however1 for percolation by pure water does not continue uninterrupted for any length of time4 ,the rise of the capillary water in the soil will1 under normal conditions1 enable the soil to reabsorb more of the ordinary mineral constituents than is removed by percolating waters4 ,further attention will be given the matter in another chapter4 ,illustration3 ,fig4 #b4 ,another but quite different line of evidence as to the probable concentration of the soil solution is furnished by the investigation of the solubility of certain phosphates4#fd ,it is popularly supposed that when superphosphate containing mono-calcium phosphate1 ,ca,h7,,po74,h,o1 is added to a soil there is a more or less permanent increase of readily soluble phosphoric acid in the soil1 although a part 8inverts0 to the somewhat less soluble dicalcium phosphate1 ,ca,h7,,po7#b;,h,o4 ,such probably is far from a correct view of what actually takes place4 ,the results obtained by studying the solubility of the different lime phosphates in water at ordinary temperature 7#be ,c47 can be expressed in a diagram similar to the accompanying sketch1 which is much distorted for convenience in lettering4 ,as the diagram indicates1 when the concentration of the solution increases with respect to phosphoric acid1 the lime is at first less and less soluble until the point represented by ,b is reached1 then becomes more and more soluble until the point ,d is reached1 from then on becoming less and less soluble1 until the solution reaches a syrupy consistency4 ,in contact with all solutions represented by points on the line ,,de the stable solid substance which can exist is mono-calcium phosphate1 ,ca,h7,,po74,h,o4 ,along the line ,,cd the only solid which is stable and can continue to persist is the dicalcium phosphate4 ,from the point ,c the composition of the stable solid varies continuously with the concentration of the liquid solution4 ,therefore1 these solids form a series varying in composition from pure dicalcium phosphate to pure calcium hydroxide4 ,one of these basic phosphates1 as they would ordinarily be called1 has a less solubility than any other1 as indicated by the point ,b4 ,all solutions to the right of the point ,b have an acid reaction1 while all solutions to the left possess an alkaline reaction4 ,it follows from these facts that if we start with any lime phosphate corresponding to some point to the right of ,b and dilute it1 or what amounts to the same thing in case it has been added to the soil1 if we leach it1 phosphoric acid will go into solution more rapidly than will lime until the composition of the residue is that of the basic phosphate stable at ,b4 ,similarly1 if we start with a phosphate more basic1 lime will be removed more rapidly than phosphoric acid1 until the residue has the composition of the phosphate of lowest solubility4 ,from this point1 with continued leaching1 the lime and phosphoric acid will dissolve in a definite ratio1 which ratio is obviously that of the phosphate of least solubility4 ,that is to say1 if the leaching process is slow1 as would be the case under soil conditions1 the solution would have a perfectly definite concentration with respect to lime and phosphoric acid4 ,what the ratio of lime to phosphoric acid may be1 is of no particular interest in this connection1 but the order of concentration of phosphoric acid is of interest4 ,owing to serious analytical difficulties1 this has not yet been determined with any great precision1 but by interpolating on the experimentally determined curve ,,ac1 this concentration is found to be somewhere in the neighborhood of #e-aj parts per million1 figures close to those obtained for the concentration of the soil solution with respect to phosphoric acid by the previously described investigations4 #fd ,for reference to the literature and detailed discussion see3 ,the action of water and aqueous solutions upon soil phosphates1 by ,f4 ,k4 ,cameron and ,j4 ,m4 ,bell1 ,bull4 ,no4 #da1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijg4 ,under ordinary circumstances1 however1 it is not probable that lime is the dominant base controlling the concentration of phosphoric acid in the soil solution1 since the great majority of agricultural soils contain vastly more ferric oxide 7more or less hydrated7 than is equivalent to any amount of phosphoric acid that will ever be brought into the soil2 and ferric phosphates are less soluble relatively than lime phosphates4 ,investigation of the relation of ferric oxide to solutions of phosphoric acid shows that the system is quite similar in many respects to the basic lime phosphates and water just described4 ,when the ratio of iron to phosphoric acid in the solid is greater than that required by the formula of the normal phosphate1 ,fe,p,o1 the aqueous solution will have an acid reaction and contain a mere trace of iron and an amount of phosphoric acid determinedly the composition of the solid and by the proportion of solid to water4 ,the basic ferric phosphates seem to be solid solutions which yield a very dilute aqueous solution when brought into contact with water4 ,what the concentration will be under soil conditions is shown by the percolation experiments cited above4 ,the addition of other substances will in many cases affect more or less the solubility of the soil minerals4 ,if these substances be electrolytes1 they will generally1 but not always1 affect the solubility of the minerals as would be anticipated from the hypothesis of electrolytic dissociation4 ,thus1 the addition of potassium sulphate lessens the solubility and hydrolysis of a potash feldspar or a potash mica4 ,contrary1 however1 to the indications of the hypothesis1 sodium nitrate decreases the solubility of a ferric phosphate4 ,while appreciable solubility effects take place with sufficiently high concentrations1 laboratory experiments indicate that the addition of such substances1 even in a liberal application of fertilizers1 is not sufficient to produce any great effect on the concentration of the soil solution4 ,similarly1 it has often been supposed that the ammonia1 and nitrous and nitric oxides of the atmosphere carried into the soil by rain1 or formed in the soil by bacterial action1 affect the solubility of the soil minerals1 but it is highly improbable that the concentration with respect to these agents ever becomes sufficiently high1 as laboratory investigations show to be necessary to affect appreciably the solubility of the ordinary rock- or soil-forming minerals4 ,rain brings from the atmosphere into the soil two agents1 however1 which do markedly affect the solubility of the soil minerals1 namely1 oxygen and carbon dioxide4 ,the atmosphere within the soil contains normally a somewhat smaller proportion of oxygen than does the air above the soil4 ,rain in falling through the air absorbs or dissolves relatively more oxygen than nitrogen4 ,therefore when the rain water has penetrated the soil to any considerable depth there should be1 and probably is1 a liberation of dissolved oxygen into the atmosphere of the soil interstices4 ,this dissolved oxygen in becoming liberated or when dissolved in the film water appears to be especially active towards the ferrous or ferro-magnesian silicates4 ,these minerals are1 moreover1 as a class probably the most soluble of the rock-forming silicates4 ,consequently oxygen brought into the soil in this manner is one of the most important agencies in breaking down and decomposing such minerals as the amphiboles1 pyroxenes1 chlorites1 certain serpentines1 phlogopites and biotites2 at the same time there is formed ferric oxide 7more or less hydrated7 and silica 7probably as quartz7 and magnesium1 potassium1 calcium or sodium pass into solution1 probably as bicarbonates4 ,that the concentration of the soil moisture may thus be made temporarily abnormal is not impossible1 though scarcely probable4 ,the soil atmosphere has normally a decidedly higher content of carbon dioxide than the atmosphere above the soil4 ,consequently the soil water is always more or less 8charged0 with carbon dioxide1 and the presence of the carbon dioxide decidedly augments the solvent powers of the water towards a great many and different kinds of rock-forming or soil minerals4#fe #fe ,for references to the literature see ,bull4 ,no4 #cj1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 of ,agriculture2 also1 ,the action of carbon dioxide under pressure upon a few metal hydroxides at #j ,c41 by ,f4 ,k4 ,cameron and ,w4 ,o4 ,robinson1 ,jour4 phys4 chem41 #ab1 #efa-egc1 7#aijh72 ,the influence of colloids and fine suspensions on the solubility of gases in water1 ,part ,i4 ,solubility of carbon dioxide and nitrous oxide1 by ,alexander ,findlay and ,henry ,jermain ,maude ,creighton1 ,trans4 ,chem4 ,soc41 #ig1 #ecf-efa1 7#aiaj74 ,what the mechanism of the reaction may be is far from clear4 ,the obvious explanation1 at least in the case of the ordinary silicates of the alkalis or alkaline earths1 is that by forming bicarbonates of the hydrolyzed bases1 the active mass of the reaction product with water is decreased and hydrolysis thereby increased4 ,but this explanation is apparently insufficient to account for the effects sometimes observed4 ,it has been shown that the passage of carbon dioxide through solutions of the silicates1 will produce more or less slowly a precipitation of silica1 and there seems little reason to doubt that it does induce to some degree a decomposition and consequent greater solubility of the silicates of the alkalis and alkaline earths4 ,it also increases to an appreciable extent the solubility of the phosphates of iron1 alumina1 and lime4 ,therefore1 the variation in the content of carbon dioxide in different soils1 and its continual variation from time to time in any one soil1 must be expected to produce corresponding changes in the soil solution with respect to such bases as potassium and lime1 and also with respect to phosphoric acid4 ,this has been verified experimentally with aqueous extracts of soils1 the solutions being charged with carbon dioxide while in contact with the soils4#ff ,it is not conceivable1 however1 that any great difference can exist in the partial pressures of carbon dioxide in different soils which are in a condition to support crops1 and therefore great absolute differences in the mineral content of the soil solution are not to be anticipated1 nor are they actually observed4 #ff ,see1 for instance1 the results obtained by ,peter1 ,proceedings of the #aith ,annual ,convention of the ,association of ,american ,agricultural ,colleges and ,experiment ,stations1 ,bull4 ,no4 #afd1 ,office of ,experiment ,stations1 ,u4 ,s4 ,dept4 ,agriculture1 #aijf1 p4 #aea et seq4 ,it has long been held that the organic substances in the soil have an important solvent effect on the minerals4 ,this assumption seems quite unwarranted in the light of our present knowledge1 although it is not to be denied that occasionally there may be present in the soil some soluble organic substance which influences the mineral content4 ,generally it has been assumed that the effective organic substances influencing the solubility of the minerals are organic acids1 of which a number have found their way into past and even current literature1 and which have been designated as humic1 ulmic1 crenic1 apocrenic1 azohumic acids1 etc4 ,their existence has been predicated upon two facts3 ,first1 humus is soluble in alkaline solutions but is more or less completely reprecipitated on the addition of an excess of a strong mineral acid1 a phenomenon also characteristic of many organic acids4 ,but many other organic substances than acids are also soluble in the presence of alkalis and insoluble in the presence of an excess of strong mineral acids4 ,second1 organic-copper complexes have been obtained from humus constituents1 and supposed to be copper salts of various humus acids4 ,the descriptions of these complexes so far given do not show that they met the usual criteria for definite compounds1 but indicate on the contrary that they were the results of absorption or possibly adsorption phenomena4 ,consequently the existence of 8humic0 acids is purely hypothetical and without experimental or other scientific verification1 and calls for no further consideration here4 ,it is a widespread and popular notion that substances with a slight solubility also dissolve slowly1 and that consequently the solubility of the minerals in the soil water must necessarily be a very slow process4 ,this is1 however1 a misapprehension4 ,it has been shown with a number of the common rock-forming minerals1 that if they be powdered and then stirred into a relatively small volume of water1 they dissolve very rapidly at first1 and in a very short time1 generally a few minutes1 the solution is nearly saturated with respect to the mineral4 ,complete saturation1 however1 may require many days4 ,the general shape of curve expressing the rate of solubility is shown in the accompanying figure4#fg ,for soils1 this fact has been verified repeatedly1 in the following way3 ,a cell fitted with parallel electrodes is placed in circuit with a slide-wire#fh or ,wheatstone bridge in such a manner that the resistance of the cell contents can be quickly determined4 ,distilled water is then placed in the cell and its resistance found4 ,generally this will be upwards of #ajj1jjj ohms4 ,the soil or rock powder under examination is then added to the cell1 being rapidly stirred into the water contained therein4 ,the resistance drops to about #e1jjj ohms within a short space of time1 usually three or four minutes4 ,a further slight drop in the resistance generally takes place1 but it requires days1 and sometimes even months to become more than barely appreciable4 ,in this manner it has been shown that the soil and many of the common soil minerals dissolve quite rapidly if they are sufficiently fine to offer a large surface to the action of the water4 ,it would seem to follow1 therefore1 that in the case of the soil solution the concentration with respect to these constituents derived from the soil minerals1 will be rapidly restored whenever disturbed through absorption by plants1 leaching1 or otherwise4 #fg ,see1 for example1 ,umwandlung des ,feldspars in ,sericit 7,kaliglimmer7 von ,carl ,benedick1 ,bull4 ,geol4 ,inst4 ,upsala1 #g1 #bgh-bhf1 7#aijd74 #fh ,see ,electrical instruments for determining the moisture1 temperature and soluble salt content of soils1 by ,l4 ,j4 ,briggs1 ,bull4 ,no4 #ae1 and the electric bridge for the determination of soluble salts in soils1 by ,r4 ,o4 ,e4 ,davis and ,h4 ,bryan1 ,bull4 ,no4 #fa1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture4 ,illustration3 ,fig4 #c4 ,that the minerals of the soil1 or a powdered mineral or rock-powder1 will dissolve continually as the concentration of the solution in contact with it is disturbed by abstraction of a dissolved mineral substance1 has been shown by numerous experimenters4 ,an apparently obvious way to test this point would be to treat the soil sample with successive portions of water1 and to analyze the successive portions for the dissolved mineral substances4 ,this method1 however1 involves serious experimental difficulties1 owing to the smaller sized mineral particles being suspended in the mother liquor1 thus precluding satisfactory decantation and clogging filters4 ,moreover1 such a process in no case simulates field conditions4 ,to meet these difficulties1 the soil or mineral powder has been placed between two porous media1 as in the space between two concentric cylinders of unglazed porcelain1 the space being closed by a rubber stopper4 ,to the interior cylinder is fitted a stopper carrying a tube of insoluble metal1 such as platinum or tin4 ,this tube is bent into a goose-neck form1 and just below the stopper the tube is perforated with a small opening4 ,the whole apparatus is filled with water and set in a beaker1 also filled with water4 ,the metal tube is made the cathode in an electric circuit1 a platinum or other suitable anode being introduced into the beaker4 ,in a few minutes the dissolved and hydrolyzed bases pass into the cathode chamber1 and as the water also accumulates in the chamber by electrolytic endosmosis1 a solution of the bases dissolved from the soil minerals drops from the end of the metal goose-neck4 ,by adding water to the outer beaker from time to time1 a steady stream of alkaline solution has been obtained for months1 and in no case yet has a soil thus treated failed to continue to yield up the bases it contains in its mineral particles4 ,the acids1 such as phosphoric acid for example1 are of course found in the water outside the porous cells1 and in the case of the phosphoric acid it also appears to continue indefinitely to be withdrawn from the soil4#fi ,it thus appears that as the products of solution and hydrolysis are removed1 by such an endosmotic device as that just described or by the roots of growing plants1 by leaching or otherwise1 the soil minerals will continue to dissolve4 #fi ,for detailed description of the apparatus and experimental data1 see ,bull4 ,no4 #cj1 p4 #bg1 et seq41 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture4 ,the foregoing arguments as to the concentration of the soil solution with respect to those constituents derived from the soil minerals1 are based on the generally recognized principle that a material system left to itself tends towards a condition of stable equilibrium or final rest1 that is1 a condition where such changes as are taking place are so balanced that no change occurs in the system as a whole4 ,but the soil is a system continually subject to outside forces and influences1 and as pointed out above1 is of necessity a dynamic system4 ,it is doubtful in the extreme if any soil in place is ever in a state of final stable equilibrium4 ,it would be natural1 therefore1 to expect and to find that even if the solution in the soil were dependent on the solubility of the soil minerals alone and were continually tending towards a definite normal concentration1 actually this concentration would seldom if ever be realized4 ,most important in this connection is the fact that the concentration of the soil solution is always dependent in some degree upon the concentration of the soluble constituents in the solid phases in other than definite chemical combinations4 ,other factors affecting the concentration of the mineral constituents in the soil solution are always existent1 and theoretically at least1 can not be ignored4 ,nevertheless a priori reasoning as well as the experimental evidence at hand indicates that the various processes taking place in the soil as a whole continually tend to form and maintain a normal concentration of mineral constituents in the soil solution4 ,chapter ,,viii4 ,,absorption ,,by ,,soils4 ,a property of soils1 affecting profoundly the composition and concentration of the soil solution1 is absorption4#gj ,it is generally recognized that soils are good absorbers for vapors1 and this fact finds practical expression in the common practice of burying things with a disagreeable odor1 such as animal carcasses1 night-soil1 etc4 ,it is also well-known that dissolved as well as suspended material can be more or less completely removed from water by passing it through sand or soil1 and this fact finds important application in water supplies for cities and towns1 sewage disposal1 etc4 ,it was known as long ago as ,aristotle's time that ordinary salt is partly removed from water by passing through sand or soil4 ,in recent times the practical as well as theoretical importance of this phenomenon has led to considerable study and experimental research1 so that our knowledge of absorption effects is now fairly extensive1 though it can hardly be claimed that it is satisfactory4 ,the absorption of a dissolved substance from solution by a soil may be one or more of at least three kinds of phenomena4 ,it may be a mechanical inclusion or trapping1 distinguished by the term imbibition1 the most familiar and striking case being the absorption of water itself by soil or sponge or similar medium4 ,it may be a partial taking up of the dissolved substance to form a new compound or a solid solution1#ga as probably is the absorption of phosphoric acid by lime or ferric oxide4 ,or it may be a condensation or concentration of the dissolved substance on or about the surface of the absorbing medium1 a phenomenon known as adsorption4 ,to prove the existence of adsorption definitely and conclusively in any given case is always difficult1 if ever possible1 but the existence of this phenomenon is the most logical explanation of many observations1 and is generally admitted by chemists and physicists at the present time4#gb ,it is by adsorption1 probably1 that potash and ammonia are held by the soil when added in fertilizers4 #gj ,for a detailed discussion and citations of the literature1 see3 ,absorption of vapors and gases by soils1 by ,h4 ,e4 ,patten and ,f4 ,e4 ,gallagher1 ,bull4 ,no4 #ea2 and ,absorption by soils1 by ,h4 ,e4 ,patten and ,w4 ,h4 ,waggaman1 ,bull4 ,no4 #eb1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijh4 #ga ,that is1 a homogeneous solid1 which may be either crystalline or amorphous4 ,probably the readiest criterion for distinguishing between a definite compound and a solid solution1 is that the former is stable in contact with a liquid solution of its constituents over a measurable range of concentrations1 while the composition of the solid solution changes with every change in the concentration of the liquid solution in contact with it4 #gb ,a clear and apparently indisputable case of adsorption has been noted by ,patten 7,some surface factors affecting distribution1 ,trans4 ,am4 ,electrochem4 ,soc41 #aj1 #fg-gd1 7#aijf74 ,on adding powdered quartz to an aqueous solution of gentian violet1 there is a distribution of the dye between the water and the quartz4 ,a microscopic examination of the latter showed that the dye was concentrated in thin layers upon the surface of the quartz grains1 from which it could be washed with water1 no change in the quartz grains being noticeable4 ,that absorption is dependent in some manner upon the solubility of the dissolved substance in the particular solvent employed would seem to be obvious4 ,but what the relation may be1 if it exists at all1 is not known4 ,for instance1 silk absorbs picric acid from solutions in water and alcohol but not from solutions in benzene1 although the solubility of picric acid in benzene lies between its solubility in water and in alcohol4#gc #gc ,absorption of dilute acids by silk1 by ,james ,walker and ,james ,r4 ,appleyard1 ,jour4 ,chem4 ,soc41 #fi1 #accd-acdi1 7#ahif74 ,the absorption of any given dissolved substance from different solvents is markedly different4 ,most soils absorb methylene blue from aqueous solutions with great avidity1 but washing out the absorbed dye with water is an extremely tedious and unsatisfactory process1 although the dye can be readily and more or less completely removed from the soil by alcohol4 ,as might be anticipated from this1 it is known that the presence of one dissolved substance affects the absorption of another1 but in what way can not1 generally1 be anticipated1 although it would seem that the importance of this subject for manurial practice would invite further research4 ,from the same solution1 different absorbents remove a dissolved substance in different degrees4 ,speaking generally1 paper absorbs dyes more readily than do soils1 while soils absorb bases more readily than does paper4 ,hence the reddening of litmus paper when in contact with a moist soil4 ,heavy soils or soils containing much hydrated ferric oxide absorb bases more readily than do light soils1 but this is probably owing to relative amounts of surface exposed1 for the same relation holds true with respect to phosphoric acid4 ,soils rich in humus are better absorbers than soils not so rich4 ,but here again there is yet doubt as to whether the explanation lies in the amount or in the kind of surface acting4 ,from the same solvent different dissolved substances are absorbed quite differently by any given absorbent4 ,this can be readily illustrated again by dyes4 ,if an aqueous solution of a mixture of methylene blue and sodium eosine1 for instance1 be shaken up with a soil1 or percolated through a column of soil1 the methylene blue is absorbed the more quickly and completely and a partial separation of the two dyes can be readily effected1 the separation being more or less complete according to the conditions of the experiment4 ,in the same manner two salts in solution can be separated partially at least4#gd ,soils absorb potassium more readily than sodium2 magnesium more readily than lime2 and ammonia more readily than any of these bases4#ge #gd ,for a number of interesting examples1 see1 ,ueber das ,aufsteigen von ,salzlsungen in ,filtrirpapier1 von ,emil ,fischer und ,edward ,schmidmer1 ,liebig's ,annalen der ,chemie1 #bgb1 #aef-afi1 7#ahic74 #ge ,the prompt absorption of a base by soils is shown by the following experiment3 ,to some freshly boiled distilled water add several drops of alcoholic phenolphthalein1 and then just enough base to produce a decided red color4 ,if the solution be now passed through a short column of soil1 cotton1 shredded filter-paper or similar absorbent1 the percolate will be perfectly colorless4 ,the red color will be restored1 however1 by adding a little of the base to the percolate4 ,the absorption from aqueous solutions of inorganic salts involves a most interesting complication4 ,just as a mixture of two or more dyes or salts in solution can be separated by the selective action of an absorbent1 so can an electrolyte itself be decomposed or resolved4 ,thus1 if a solution of potassium chloride be passed through a column of soil1 or cotton1 or paper1 or any similar absorbent1 the filtrate will not only be less concentrated than the original solution1 but the potassium will be found to have been absorbed to a greater extent than the chlorine1 that is1 the percolate contains free hydrochloric acid4 ,the importance of this phenomenon for the conservation of the desirable constituents of manurial salts1 and the elimination or leaching out of the less desirable constituents is obviously great4 ,equally great perhaps1 is the effect upon the reaction of the soil1 whether it be rendered temporarily alkaline or acid1 an effect of the very greatest importance for the growth of some of our common crop plants#gf and for the lower soil organisms1 such as the bacteria1 molds1 together with ferments1 enzymes1 etc41 many of which are very sensitive to the reaction of the media in which they may be1 and which in turn are of undoubted importance in determining the fertility of the soil for higher plants4 #gf ,see1 ,the toxic action of acids and salts on seedlings1 by ,f4 ,k4 ,cameron and ,j4 ,f4 ,breazeale1 ,jour4 ,phys4 ,chem41 #h1 #a-ac1 7#aijd74 ,it is quite conceivable1 for instance1 that if the drainage conditions were not exceptionally good under a heavy type of soil1 it might be rendered temporarily unfit for clover or alfalfa by a heavy application of potassium salts or of sodium nitrate4 ,the idea put forward by some authorities that too long continued or over fertilizing renders soils acid1 may have better foundation than their theoretical reasoning would seem to warrant4 ,the absorption of a dissolved substance from solution by an absorbent is in effect a distribution phenomenon and the simplest formula to give quantitative expression to such a distribution is ,c_/,c ,k when ,c is the concentration in the liquid phase and ,c the concentration in the solid phase1 ,k being a characteristic constant for the particular case under consideration4 ,when a chemical reaction or a change of state1 chemical or physical1 is involved in the absorption in either dissolved substance or absorbent the formula becomes ,c_/,c ,k when n is a function which may be very simple or very complex4 ,attempts to develop a precise formula of this general type for the absorption by some given soil1 although such a formula would be desirable for theoretical and practical reasons alike1 have uniformly failed4 ,a sufficient reason for this failure seems to lie in the fact that most dissolved substances produce an appreciable effect on the granulation or flocculation of the soil particles1 which is progressive with the absorption so that a continual change of absorbing or effective surface is taking place as the absorption proceeds4#gg ,moreover1 in the case of an absorption1 with the formation of a continuous film of the dissolved substance1 a new kind of absorbing surface is developed4 ,hence n is a function of so difficult a character as to defy thus far any attempt at formulation4#gh #gg ,that mineral fertilizers have a decided influence on the granulation of soils and the properties dependent thereon1 and that this is of practical importance1 is gradually coming to be recognized2 see1 for instance1 ,ein ,beitrag zur ,kenntnis der ,wirkung knstlicher ,dnger auf die ,durchlssigkeit des ,bodens fr ,wasser1 von ,edwin ,blanck1 ,landw4 ,jahrb41 #ch1 #hfc-hfi1 7#aiji71 and the literature there cited4 ,dr4 ,r4 ,o4 ,e4 ,davis in a yet unpublished investigation has shown that the addition of soluble salts produces decided effects upon the soil-moisture relations which affect crop production4 ,the critical moisture content is displaced1 the penetrability1 permeability1 specific volume1 vapor tension1 etc41 are affected in measurable degree1 and it appears that the physical functions of mineral fertilizers are much greater in amount and importance than has been popularly assumed4 #gh ,the distribution of solute between water and soil1 by ,f4 ,k4 ,cameron and ,h4 ,e4 ,patten1 ,jour4 ,phys4 ,chem41 #aa1 #eha-eic1 7#aijg74 ,we cannot therefore predict in any quantitative way what will be the distribution of a soluble substance such as salts in commercial fertilizers1 for instance1 between the solid soil particles and the soil solution4 ,empirical experiments show1 however1 that with the amount of a soluble salt present under normal conditions in a humid climate1 or as used in fertilizer practice1 the absorption of ammonia1 lime1 potassium or phosphoric acid is relatively very great1 and in a general way in about the order named4 ,absorption is not an instantaneous process4 ,however1 the rate at which a dissolved substance is absorbed is generally quite rapid4 ,that is1 if a soil be stirred or mixed with an aqueous solution1 the absorption takes place very quickly1 in the absence of any outside disturbing influences4 ,the law governing the rate of absorption by soils has not therefore possessed any great practical interest and has not been studied from a quantitative point of view1 although it is known qualitatively that the rate is increased by increasing the concentration of the solution1 or by increasing the amount of the absorbent or at least its effective surface4 ,two rate equations are of interest in this connection1 and have been carefully studied4 ,the rate at which a salt or other dissolved substance will advance into an absorbing soil from a solution is given by the same equation as that describing the rate of advance of the water itself1 y kt where y is the distance and t the time4#gi ,the constants n and k for the slower moving dissolved substance are different from those for the water4 ,this equation has probably little importance for ordinary agriculture1 for absorption by the soil from a large 7and relatively illimitable7 mass of solution is unusual4 ,that it may have considerable importance in seepage1 irrigation1 and some soil engineering problems1 seems quite likely4 ,the rate at which a soil will absorb a dissolved substance from a percolating solution is given by the equation dx ---------- ,k7,a - x71 dt as has been pointed out above4#hj ,more interesting and important1 however1 is the fact that this same equation describes the rate at which an absorbed substance is removed from the soil by leaching4 ,in the case of soils in humid areas dx_/dt rapidly becomes exceedingly small as x approaches ,a1 that is1 when the amount of soluble material in the soil becomes small1 and is practically constant under such conditions1 as has been pointed out above when describing the removal of potassium and phosphoric acid from soils by percolating waters4 ,this formula has a special interest in considering the reclamation of alkali lands by underdrainage1 a problem to which reference will be made later4 #gi ,see formula1 page #bh4 #hj ,see formula1 page #dg4 ,both percolation experiments1 as those cited above1 and direct absorption experiments made by shaking up soils with solutions of the salts in question1 show conclusively that the absorption phenomena taking place in the soil are in harmony with the direct solubility effects in tending to produce and maintain a solution of a normal concentration as regards those constituents which it happens are also derived from the soil minerals4#ha ,it is an interesting coincidence that nitric acid 7in combination with various bases of course7 is very little absorbed by most soils1 and does vary in concentration1 not only in different soils but in the same soil1 between wide limits1 and within short intervals of time4#hb ,the nitrates of the soil are not derived from minerals1 and should more properly be considered with the organic constituents of the soil solution4 #ha ,an extreme case is worth citing in this connection4 ,mr4 ,w4 ,h4 ,heileman in studying the influence of various kinds of alkali upon plant growth1 added from #c-d per cent4 of sodium carbonate to soils known to be otherwise free from alkali4 ,wheat seedlings grown in the soils so treated showed no ill effects from the added salt4 ,when distilled water was percolated slowly through the soils1 or shaken up with them1 the resulting solution contained the merest traces of the alkali4 ,the ordinary method of determining the lime requirement of a soil by adding lime water until the solution shows an alkaline reaction1 is another obvious absorption phenomenon1 and is not dependent1 as popularly supposed1 upon the presence of acids in the soil4 ,soils which by no possibility could contain any free acid1 frequently absorb very large amounts of lime in this manner4 #hb ,usually1 in the growing season1 the soil solution has a much higher concentration with respect to nitrates in the morning than it has in the evening4 ,an important application of these views concerning absorption arises in connection with certain widespread notions concerning soil acidity4 ,there is a popular belief that most soils are acid1 that the soil solution contains some free acid1 mineral or organic1 other than dissolved carbon dioxide1 and that a neutral or alkaline solution is necessary to the successful production of most of our crops4 ,this belief is1 however1 unwarranted1 for the vast majority of soils yield an aqueous extract which is alkaline when boiled to expel carbon dioxide1 and some of our crops1 for instance wheat1 seem to thrive better in a slightly acid medium4 ,this popular fallacy seems to have its origin in the fact that most soils when moistened and pressed against blue litmus paper1 redden it4 ,this reddening may sometimes be due to the actual presence of some acid1 or to dissolved carbon dioxide1 but is undoubtedly due in the majority of cases to selective absorption4 ,litmus is a red dye of an acid-like character1 which forms a soluble blue salt with the ordinary bases4 ,but it has been shown that most soils are better absorbents of bases than is paper1 whereas paper is a better absorbent of dye1 speaking generally1 than is a soil4 ,consequently when moist soil is brought into contact with wetted blue litmus paper the base is absorbed more readily by the soil1 and the dye by the paper1 the latter therefore becoming reddened4 ,the reddening of blue or 8neutral0 litmus paper can be accomplished with various absorbents4 ,by pressing the litmus paper between moistened wads of absorbent cotton the reddening can be readily accomplished1 usually in the course of ten minutes to a half hour4 ,that the phenomenon is not due to any adhering acid on the cotton can be shown in the following way3 ,a litmus solution is carefully prepared so that there is a very small excess of base present over that required to give the blue color4 ,a wad of absorbent cotton is carefully washed by repeatedly sousing it in distilled water from which carbon dioxide has been expelled by boiling4 ,when the cotton has been thoroughly washed1 it is stirred thoroughly in a portion of distilled water1 free from carbon dioxide1 then withdrawn by some appropriate instrument and allowed to drain for a few minutes4 ,the litmus is added in fairly large quantity to the drainings1 which should then have a blue color4 ,again stir the cotton in the water1 and more or less quickly1 depending on the amount and purity of the litmus preparation as well as the quantity of cotton used1 the solution will become red4 ,the only criterion for determining surely that a soil is acid1 is to make an aqueous extract1 expel the dissolved carbon dioxide by boiling1 or by passing through the solution an inactive gas1 such as nitrogen1 and then to test the reaction of the solution4 ,acid soils undoubtedly do exist1 but they are by no means common or widespread1 and are to be regarded as exceptional and abnormal4 ,the phenomena of selective absorption suggest the important part which surfaces play in modifying and changing chemical reactions4#hc ,for instance1 ,becquerel#hd observed that a solution of copper nitrate or cobalt chloride diffusing from a cracked test-tube placed in a solution of sodium sulphide1 led to the formation of the corresponding sulphide1 but in the crack the metal itself was precipitated4 ,experiments of ,graham#he show that when a solution of silver nitrate is percolated through charcoal1 not only is there a selective absorption as is shown by the percolate containing free acid1 but there is a chemical reaction involved1 since the silver is deposited in metallic spangles in the interstices of the absorbent4 ,graham has shown1 and since his time others1 that often metals can be separated from solutions of their salts by such absorbents as charcoal4 ,spring#hf has shown that at bounding surfaces of dilute solutions1 chemical action is increased4 #hc ,for references to the literature see1 ,bull4 ,no4 #cj1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 p4 #fa et seq4 #hd ,note sur les rductions mtalliques produites dans les espaces capillaires1 par ,m4 ,becquerel1 ,comptes rendus1 #hb1 #ced-cef1 7#ahgf74 #he ,effects of animal charcoal on solutions1 by ,t4 ,graham1 ,quart4 ,jour4 ,sci41 ,i1 #abj-abe1 7#ahcj74 #hf ber eine ,zunahme chemischer ,energie an der freien ,oberflche flssiger ,krper1 von ,w4 ,spring1 ,zeit4 physik4 ,chem41 #d1 #feh-ffb1 7#ahhi74 ,it has been shown that the amount and kind of surface has a marked influence on the decomposition of hypochlorous acid1 carbon dioxide1 phosphine1 arsine1 and other compounds4 ,meyer and his associates1 as well as a number of other investigators1 have shown that the character of the surface of the containing vessel greatly affects the combination of hydrogen and oxygen4 ,many reactions have been investigated by van't ,hoff1 who concludes that both the nature and amount of surface exposed have an influence4 ,the inversion of sugar is affected by the nature of the walls of the containing vessel1 and its reduction by ,fehling's solution is affected both by the walls of the vessel and the amount of cuprous oxide formed in the reaction4 ,alteration in the character as well as degree of a number of reactions by having them take place in capillary spaces has been observed by ,liebreich1 ,becquerel1 ,lieving and other investigators4 ,so-called 8contact reactions10 as in the production of sulphuric acid1 are now familiar processes finding commercial applications4 ,and the solubility of some substances at least1 notably gypsum1 has been shown to vary considerably with the size and consequent shape of the particles in the solid substance in contact with its solution4#hg #hg ,see especially1 ,beziehungen zwischen ,oberflchenspannung und ,lslichkeit1 von ,g4 ,a4 ,hulett1 ,zeit4 ,phys4 ,chem41 #cg1 #che-djf1 7#aija74 ,lslichkeit und ,lslichkeits ,beeinflussung1 von ,v4 ,rothmund1 p4 #aji1 7#aijg72 ,principles thoretiques des methodes d'analyse minerale1 par ,g4 ,chesneau1 p4 #af-be1 7#aijf74 ,it has been shown that some soils will at times produce the blue coloration in alcoholic solutions of guiac1 which is characteristic of oxidases1 and yellow aloin solutions are sometimes colored red4 ,hydrogen peroxide is decomposed by some soils even after they have been thoroughly ignited to get rid of all organic matter4 ,but in how far these effects may be due to surface influences can not be positively stated2 yet uncompleted investigations by ,dr4 ,m4 ,x4 ,sullivan indicate that some of these phenomena at least must be attributed to specific influences 7although probably of catalytic character7 of particular soil components1 such possibly as manganous oxide or ferric oxide2 but the mechanism of the reactions is as yet largely speculative4 ,the soil is composed in large part of very fine particles of rounded shape1 exposing relatively an enormous surface to the soil solution1 and normally this solution is mainly under capillary conditions1 so that we should expect that many reactions would take place quite differently in the soil from the way they would in a beaker or flask4 ,this fact has been generally overlooked or ignored1 and is probably the explanation of many of the apparently anomalous results hitherto reported in chemical investigations of soils4 ,abnormal solubilities1 precipitations1 oxidations or reductions are frequently found in the literature1 and when their abnormality is noted at all1 they are too often and with slight show of reason ascribed to indefinite bacterial action or more mysterious vital agencies4 ,many of them are undoubtedly the results of surface actions4 ,unfortunately1 aside from some few studies of absorption phenomena1 surface effects have received little or no attention from soil investigators1 although obviously one of the most important and apparently fruitful fields1 requiring immediate attention4 ,enough is known to justify the statement that the chemistry of the soil need not be1 and probably is not1 the chemistry of the beaker4 ,chapter ,,ix4 ,,the ,,relation ,,of ,,plant ,,growth ,,to ,,concentration4 ,that the concentration of the mineral constituents in the soil solution under normal conditions is competent for plant support1 is shown by numerous experiments4 ,birner and ,lucanus#hh in an experiment that has long since become classic1 found that they could raise wheat to maturity in a well-water1 the concentration of which was approximately #ah parts per million with respect to potassium1 and #b parts per million with respect to phosphoric acid1 while the corresponding concentrations of the soil solution are normally about #be-cj parts per million of potassium and #f-h parts per million of phosphoric acid4 ,nevertheless ,birner and ,lucanus report that the wheat grown in the well-water throve even better than that grown at the same time in a rich garden mold4 ,since then many investigators in numerous trials have obtained similar results4 ,recently wheat1 corn1 and some of the common grasses have been grown to a satisfactory maturity in tap water with a concentration of about #g parts per million of potassium and #j4e parts per million of phosphoric acid4 ,and repeatedly wheat plants1 grasses1 cowpeas1 vetches1 potatoes and other plants have grown in a satisfactory way in solutions made by shaking up a soil in distilled water and separating from the solid particles by means of filters of unglazed porcelain4 #hh ,wasserculturversuche mit ,hafer1 von ,dr4 ,birner und ,dr4 ,lucanus1 ,landw4 ,vers4-,sta41 #h1 #abh-agg1 7#ahff74 ,there can be no doubt1 therefore1 that the soil solution is normally of a concentration amply sufficient to support ordinary crop plants1 and is maintained at a sufficient concentration1 so far as mineral plant nutrients are concerned4 ,undoubtedly1 however1 variations in the concentration of the soil solution can1 and often do1 take place1 and the results of laboratory experiment indicate that they probably produce effects on plants4 ,it has been shown in water-culture experiments with wheat1 that if a given ratio of mineral nutrients be maintained1 relatively small effect is produced on the growing plants by varying the concentration over a wide range1 in one case from #ge parts per million to #gej parts per million1#hi and this effect seems to be largely independent of the nature of the particular mixture of solutes4 ,but varying the relative proportions of the mineral constituents has been shown by numerous experiments to produce very marked changes in the growth of plants4 ,not only does a control of the concentration and proportion of the mineral constituents of a solution produce a more rapid1 or a slower growth1 a greater or lesser total growth1 but it produces differences in the character of growth2 as for instance1 causing the tops to grow relatively faster than the roots1 or vice versa4 ,however1 many effects of this type can be produced1 and sometimes more readily1 by soluble organic substances1 or mechanical agencies4 ,the mechanism of these effects is by no means clear1 in many cases4 ,that other causes obtain than a sufficient supply of mineral nutrients will be shown in the following chapters4 ,experiments with wheat seedlings in water cultures1 where the weights of the green tops were taken as the measure of growth1 showed that the most-favorable ratio was one of phosphoric acid 7,,po7 to three or four of potassium 7,k71 about the ratio which has been found to exist normally in the soil solution of humid areas of the ,united ,states1 namely1 #f-h parts per million of phosphoric acid to #be-cj parts per million of potassium4 #hi ,effect of the concentration of the nutrient solution upon wheat cultures1 by ,j4 ,f4 ,breazeale1 ,science1 n4 s41 #bb1 #adf-adi1 7#aije74 ,all growing plants require for their growth and development various organic compounds containing carbon1 hydrogen1 oxygen and nitrogen4 ,the higher crop plants with which agricultural investigations appear to be more immediately concerned1 seem to have inherent power to produce these needed substances within themselves4 ,but it is becoming more and more evident that the large problem of soil fertility1 or the relation of the soil to crop production1 frequently if not generally involves the growth and development of lower organisms including ferments and bacteria4 ,these may or may not in particular cases1 favor the growth of the desired higher plants4 ,many of these lower organisms require certain organic compounds or thrive better if these are brought to them in the soil solution1 and indeed evidence is not lacking that such may sometimes be the case even with the higher plants4 ,certainly their growth can be much affected by the presence of different organic substances in the nutrient solution4 ,enough work has been done in this field of investigation to show that the concentration of the soil solution or artificial nutrient solution with respect to the organic compounds must generally be low2 too high a concentration always inhibits growth or even produces death2 and there is probably an optimum concentration1 or one at which the plant will grow best2 but this optimum concentration varies with the specific nature of the plant1 the presence of other dissolved substances1 mineral or organic1 and possibly with other factors4 ,while a notable amount of work has thus been done in a field of inquiry obviously of practical as well as theoretical interest1 almost no definite information has as yet been obtained as to the concentration of organic substances in the soil solution1 or its effect upon plants under field conditions1 excepting in the case of the nitrates1 the products of bacterial activities4 ,the concentration with respect to nitrates is known to vary greatly from a few parts to several thousand parts per million1 and this sometimes within a few days or even hours4 ,the great changes in concentration with respect to nitrates1 the rapidity of the changes1 and the correspondingly large effects on growing plants make this a subject requiring special treatment by itself4 ,this at present seems more easily appreciated from a consideration of the bacteria involved1 and will not be discussed more fully here4#ij #ij ,see3 ,the fixation of atmospheric nitrogen by bacteria1 by ,j4 ,g4 ,lipman1 ,bull4 ,no4 #ha1 ,bureau of ,chemistry1 ,u4 ,s4 ,dept4 of ,agriculture1 #aijd2 ,a review of investigations in soil bacteriology1 by ,edward ,b4 ,voorhees and ,jacob ,g4 ,lipman1 ,bull4 ,no4 #aid1 ,office of ,experiment ,stations1 ,u4 ,s4 ,dept4 of ,agriculture1 #aijg2 ,the physiology of plants1 by ,w4 ,pfeffer1 translated by ,a4 ,j4 ,ewart1 vol4 ,i1 p4 #chh et seq41 #aijj2 ,the effect of partial sterilization of soil on the production of plant food1 by ,edward ,john ,russell and ,henry ,brougham ,hutchinson1 ,jour4 ,agric4 ,sci41 #c1 #aaa-add1 7#aiji74 ,of the ash constituents of plants1 there must be in the soil solution1 potassium1 magnesium1 phosphorus1 sulphur and iron for any plant growth1 and for the higher crop plants1 calcium must also be present4 ,of these1 iron is usually present in barely appreciable concentration and more than this is not desirable1 or is even harmful for common crop plants4 ,under the normal conditions for soils in humid areas1 sulphur also is usually present in scarcely more than appreciable quantities and there is no positive evidence to show that higher concentrations are especially desirable1 though this may be the case for certain crops1 such for instance as the onion4 ,phosphorus is usually present to the extent of #e or #f parts per million of phosphoric acid 7,p,o71 while it has repeatedly been shown that such crops as wheat can thrive and make a good growth with a concentration a tenth of this4 ,it appears to be clear therefore that as far as food supply is concerned there is normally an ample supply of phosphorus in the soil solution2 but it does not follow that increasing the concentration of the solution if only temporarily would not result in favorable effects upon growing plants4 ,a consideration of the bases1 however1 introduces serious difficulties1 which will probably require much further research by the plant physiologist as well as the soil chemist4 ,it is impossible as yet to determine the concentrations at which different plants will not grow4 ,it is even impossible to determine the concentrations at which they will thrive best4 ,it seems certain that different crop plants require different amounts of these minerals1 but whether or not they require different concentrations of the constituents in the nutrient solution for their several best growths is yet not clearly shown4 ,it now seems probable that to some extent at least these basic mineral nutrients can replace one another for the plant's metabolism4 ,it has been shown in the case of certain lower plant organisms that potassium can be more or less successfully replaced by rubidium and caesium1 and in the case of some higher plants1 possibly calcium1 magnesium and potassium can partially replace one another4#ia ,in spite of the fact that sodium as well as potassium is a necessary constituent for the metabolism of higher animals which feed upon plants1 it is generally held that sodium can not replace potassium in the processes of plant growth1 although ,wheeler and his colleagues have advanced evidence to show that a partial replacement is possible4#ib ,it seems evident1 however1 that no generalizations can hold concerning the effect of the concentration of any one base on plant growth which do not include recognition of possible modifications due to the presence of other bases2 and the formulation of such generalizations must needs wait upon a more thorough knowledge of the parts played by the several mineral nutrients in the metabolism of different classes of plants4 #ia ,for a more detailed discussion of this subject1 and the functions of the several ash constituents in plant nutrition1 see3 ,the physiology of plants1 by ,w4 ,pfeffer1 translated by ,a4 ,j4 ,ewart1 vol4 ,i1 p4 #daj1 et seq41 #aijj4 #ib ,the effect of the addition of sodium to deficient amounts of potassium1 upon the growth of plants in both water and sand culture1 by ,b4 ,l4 ,hartwell1 ,h4 ,j4 ,wheeler and ,f4 ,r4 ,pember1 ,report ,rhode ,island ,agricultural ,experiment ,station1 #aijf-g1 p4 #bii-ceg4 ,as to forms or chemical combinations in which the inorganic constituents of the soil solution are best adapted to plant growth1 but little can yet be said other than that the different combinations do have an importance4 ,some empirical information is available1 such as for instance1 that potassium sulphate or carbonate is a better fertilizer for some crops than is potassium chloride4 ,it is known that the mineral nutrients in the plant are partly in inorganic combinations but largely in organic combinations4 ,but the causal relationships are yet to be worked out4 ,and finally1 although some meagre experimental data have been obtained as to the effect of certain inorganic constituents on the absorption of others1 by particular plants1 the mechanism of absorption itself1 including the selective powers of the plant1 is yet wanting an adequate explanation4 ,chapter ,x4 ,,the ,,balance ,,between ,,supply ,,and ,,removal ,,of ,,mineral ,,plant ,,nutrients4 ,the mechanism of the solution and transport of mineral nutrients developed in the preceding pages makes it of interest to determine the relation between the possible or probable supply of mineral plant nutrients and crop demands over large areas4 ,the inquiry can be formulated more specifically3 ,is the movement of mineral plant nutrients towards the surface soil equal to or in excess of the removal by drainage waters and garnered crops8 ,satisfactory data are yet wanting for anything like exact computations1 but approximate figures are available which appear sufficient for the present purpose4 ,the rainfall 7,r7 can be considered as disposed in three portions1 the fly-off 7f71 the run-off 7r71 and the cut-off 7c74 ,stating this as an equation1 ,r f r c4 ,the cut-off can be resolved into the portion 7a7 seeping through the soil to ultimately join the run-off1 and the portion 7b7 returning to the surface to ultimately join the fly-off4 ,stated as equations1 ,r f r a b f b 7r a74 ,in other words1 the rainfall can also be considered as made up of the fly-off1 the capillary water of the soil and the drainage from the area4 ,according to ,murray1#ic ,geikie1#id ,newell1#ie and others1 the drainage water for humid areas1 or such an area as the ,united ,states as a whole1 would be between #bj and #cj per cent4 of the rainfall1 the major portion coming from seepage water rather than surface drainage4 ,assuming the higher figure1 and making the further very probable assumption that the capillary water in the soil 7b7 is never less than the fly-off or the water that evaporates during rain 7f71 it follows from the equations given that the capillary water is at least #ce per cent4 of the rainfall4 ,if we assume the lower value for the drainage1 then the capillary water is at least #dj per cent4 of the rainfall1 and if we assume the extreme case--that the fly-off is practically negligible--the capillary water becomes #hj per cent4 of the rainfall4 ,it appears1 therefore1 that in all probability the proportion of the cut-off water which returns to the surface as film water or capillary water is always greater1 and generally much greater1 than the portion which seeps through the soil to join the run-off4 #ic ,on the total annual rainfall on the land of the globe1 and the relation of rainfall to the annual discharge of rivers1 by ,sir ,john ,murray1 ,scot4 ,geog4 ,mag41 #c1 #fe-gg1 7#ahhg74 #id ,textbook of ,geology1 by ,sir ,archibald ,geikie1 p4 #dhd1 7#aijc74 #ie ,in ,principles and conditions of the movements of ground water1 by ,f4 ,h4 ,king1 ,ann4 rept4 ,u4 ,s4 ,geol4 ,surv41 #ai1 ,,ii1 #ei-bid1 7#ahig-ih74 ,from the available data1 it appears that the average concentration of the run-off waters of the ,united ,states is about #a4h parts per million of potassium 7,k7 and about #j4f parts per million of phosphoric acid 7,,po71#if while the concentration of the capillary groundwater is some ten or twelve times greater4 ,but even if these concentrations were the same1 it is altogether probable that very much the greater part of the mineral plant nutrients dissolved by meteoric waters is continually1 if slowly1 moving towards the surface of the soil4 ,the average rainfall of the ,united ,states may be taken as approximately #cj inches4#ig ,if it be assumed that the discharge into the sea is #be per cent41 then the capillary cut-off water is at least #cg4e1 and probably nearer #gj per cent4 of the rainfall4 ,king's experimental work#ih indicates that the higher figure is much nearer the truth4 ,computing from the concentrations just cited1 with the equations given above1 it is found that approximately #c1ejj1jjj tons of potassium 7,k7 and #a1bjj1jjj tons of phosphoric acid 7,,po7 are carried into the sea annually from the ,united ,states1 while from #dh1jjj1jjj to #ajj1jjj1jjj tons of potassium and #ah1jjj1jjj to #dj1jjj1jjj tons of phosphoric acid are being carried towards the surface of the soil4 ,if it be assumed that an average of one ton per acre of dry crop containing one per cent4 potash and #j4f per cent4 phosphoric acid#ii be removed from the entire area of the ,united ,states1 then the annual loss from this source would be #bd1jjj1jjj tons of potassium and #ad1jjj1jjj tons of phosphoric acid4 ,consequently1 there is an ample margin between the losses by cropping and seepage waters1 and the supply of capillary waters4 ,it is true that cases exist where the production of vegetable matter is much greater than a ton to the acre1 productions of five tons or even more being on record4 ,but such cases occur only where the water supply is also greater1 either through natural rainfall or artificial irrigation2 and it should also be borne in mind that the production of so large a mass of green crop involves a considerable drawing power on the water in the soil in addition to the evaporation which would take place at the surface under ordinary conditions4 ,in other words1 the plant would then be playing no small part in drawing to itself its needed supplies of water and dissolved mineral nutrients4 #if ,estimated from data in ,bull4 ,no4 #ccj1 ,u4 ,s4 ,geological ,survey1 ,the data of geochemistry1 by ,frank ,wigglesworth ,clarke1 #aijh1 p4 #ec-ij4 #ig ,the latest authoritative statement is that the average annual rainfall of the ,united ,states is #bi4d inches2 see3 ,water ,resources1 by ,w4 ,j4 ,mc,gee1 vol4 #a1 p4 #ci-di1 and ,distribution of rainfall1 by ,henry ,gannett1 vol4 #b1 p4 #aj-ab1 ,report of the ,national conservation commission1 ,senate doc4 ,no4 #fgf1 #fjth ,congress1 #b;d session1 #aiji4 #ih ,king3 loc4 cit41 p4 #he4 #ii ,estimated from ,wolff's tables1 ,how crops grow1 by ,samuel ,w4 ,johnson1 #ahij1 appendix4 ,the question may be asked1 if the processes outlined above are generally operative1 why accumulations of soluble mineral substances are not usually found at the surface of the soil4 ,as a matter of fact such accumulations do occur normally when the evaporation at the surface is relatively large1 that is1 under arid conditions4 ,and under humid conditions it appears to be a general rule that the surface soil contains more readily soluble or absorbed mineral matter than do subsoils4#ajj ,no great accumulation occurs at the surface normally under humid conditions because the rainfall is sufficiently distributed throughout the year to enable the cut-off water to carry back promptly into the lower soil levels any excessive amount of soluble material1 there to start anew its slower ascent towards the surface4 #ajj ,see1 for instance3 ,investigations in soil management1 by ,f4 ,h4 ,king1 ,madison1 ,wis41 #aijd1 p4 #fb et seq4 ,this tendency towards a higher content of absorbed soluble mineral matter in the surface soil has been amply confirmed by other experiments4 ,it has been advanced as an argument against the assumption that the hydrolysis of the soil minerals is a reversible process4 ,but as pointed out elsewhere in the text1 many of the soil minerals can be made in the wet way at more or less elevated temperatures and the more rational explanation is simply that at ordinary temperatures the rate of formation is exceedingly slow4 ,calculations such as those here presented are at the best open to many objections1 and it is wise to avoid giving them too much emphasis4 ,so far as the available data justify any conclusion1 however1 it appears that the rise of capillary water is entirely capable of maintaining a sufficient supply of mineral nutrients for crop requirements2 and furthermore1 it is obvious that the problem of the supply of mineral plant nutrients is dynamic and cannot be successfully attacked by considerations which are essentially static4 ,chapter ,,xi4 ,,the ,,organic ,,constituents ,,of ,,the ,,soil ,,solution4 ,the organic substances in the soil are tissue remains1 to a large extent of plants1 and to a less extent of animals2 and it is to be expected that there may be found also in the soil the substances which were in the organisms at the time of their death1 and degradation and decomposition products derived from these4 ,moreover1 there are to be anticipated numerous products of bacterial origin1 secretions of algae1 fungi1 etc41 so that the organic complex in the soil may contain numerous substances of widely different chemical characteristics4 ,degradation products of proteins1 fats1 and carbohydrates1 as well as decomposition products may be expected in almost any soil4 ,but it does not follow that any particular organic substance 7excluding1 of course1 carbon dioxide or nitrates7 is to be found in every soil4 ,no generalization regarding the organic substances in the soil can be made such as that formulated for the inorganic compounds4 ,it is probable that further investigation will show certain organic substances or classes of substances to be common to most soils1 but it is reasonably certain that many other organic substances will be found in only a few soils1 or occasionally1 and these latter will be often a prominent factor characterizing the particular soil in which they may occur4 ,although no broad generalization is justified regarding the composition of the soil solution with respect to organic substances dissolved1 nevertheless the extension of the methods developed in the study of the inorganic substances dissolved has led to a considerable knowledge of the organic ones4 ,in view of the facts shown in the preceding chapters1 and at the same time recognizing that good and poor soils respectively must show differences in the soil solution if the fundamental thesis is valid as to the relation of soils to crop production1 experiments have been made to investigate in a comparative way solutions obtained from good and poor soils of the same type1 locality1 and physical characteristics4 ,for this purpose two samples of soil were taken from adjacent fields which had been under observation for two years4 ,the soils were of the same type1 ,cecil clay1 and were so similar in their physical characteristics as to be distinguished with difficulty in the laboratory4 ,on one field a good crop of wheat was grown1 followed by a good crop of clover and tame grasses4 ,on the other field1 the corresponding crops had been quite poor4 ,the field yielding the good crops had been plowed somewhat deeper1 and had previously received a moderate application of stable manure4 ,otherwise1 so far as could be learned1 the cultural history of the fields had been the same4 ,for convenience1 the sample from the first field will be designated 8good10 and from the other 8poor40 ,aqueous extracts from these soils were prepared1 the same proportion of distilled water to soil being taken in each case1 and the time of contact being the same4 ,the solutions were freed from suspended matter by being passed through ,pasteur-,chamberland bougies under pressure4 ,young wheat seedlings germinated at the same time1 and selected carefully for uniformity of size and apparent vigor1 were grown in these solutions for three days4 ,at the expiration of this period the seedlings in the extract from the good soil were about five inches in height1 and the roots were clear1 clean and turgid4 ,the plants in the poor extract were scarcely three inches in height1 and the roots were assuming a slimy1 unhealthy appearance and becoming flaccid at the tips4 ,the plants were then all removed1 the roots washed carefully in tap water2 the plants which had been in the poor solution were placed in the good solution1 and those which had been in the good solution were placed in the poor solution4 ,at the end of four days further1 the poor plants had surpassed in height the ones which had previously been in the good solution1 and the roots had acquired the general characteristics of healthy plants4 ,these which had been originally in the good solution and then transferred to the poor1 had made little additional growth1 and the roots had become somewhat flaccid4#aja #aja ,the success of this and of many of the following experiments was due in large measure to the skill and patience of ,mr4 ,james ,e4 ,breazeale4 ,this experiment was repeated several times1 not only with the soils cited but with samples from adjacent good and poor spots in fields on several soil types from widely separated areas2 for instance1 ,cecil clay from near ,statesville1 ,north ,carolina2 ,sassafras loam from ,maryland2 ,windsor sand from ,delaware2 and similar results were obtained4 ,in other words1 these water cultures produced plants which showed much the same differences1 in kind and degree1 as had been observed in the field4 ,this was recognized as an important step forward1 for it indicated that whatever was making a difference in the crop-producing power of these soils in the field was transmitted to their aqueous extracts1 and methods for studying the chemical properties of solutions are far in advance of methods for studying mixtures of solids4 ,the soil extracts described above were subjected to a careful analysis for their mineral constituents4 ,they were found to be practically identical in this respect4 ,further1 the poor extract contained decidedly more nitrates than the good--from three to four times as much4 ,it follows1 therefore1 that the difference in the soils which produced a good and a poor crop respectively1 was not due to a difference in mineral plant nutrients1 or other mineral differences probably1 nor to their respective content of nitrates4 ,consequently1 the poor solution was such1 not because of the lack of anything1 but because of the presence of something inimical or 8toxic0 to plant growth2 and further1 this something must be an organic substance or substances more or less soluble in water4 ,this conclusion was confirmed in the following way4 ,samples of the poor solution from the soil obtained near ,statesville1 ,n4 ,c41 were diluted twice1 five times1 and ten times1 and wheat seedlings were grown in these solutions1 using a sample of the good solution as a check4 ,it was found after several days growth that the plants in the solution diluted tenfold were about as good1 or perhaps slightly better1 than those grown in the check solution4 ,in every case diluting the poor solution had improved it for plant growth1 and the higher the dilution the greater the improvement1 in spite of the consequent dilution of the mineral plant nutrients4 ,the only explanation of these results which has yet suggested itself is that the toxic organic substances present were less effective on dilution until the concentration reached a point where they actually became stimulative1 as is common with toxins of every character4 ,another set of experiments confirmed the conclusion that the poor solution contained some organic substance inhibitory to plant growth4 ,a number of water cultures was prepared from the aqueous extract of the poor soil1 and lime in various forms was added to the cultures4 ,to two of the cultures lime carbonate and lime sulphate respectively were added in excess1 so that there was in each case a powdered solid at the bottom of the containing vessel4 ,at the end of two days the wheat seedlings which were growing in the vessels containing the powdered solids had decidedly outstripped those growing in all the others1 the tops having the appearance of unusually good and healthy plants4 ,the roots were of a very remarkable character1 being exceptionally long1 very turgid1 clear1 clean and translucent4 ,at once1 new experiments were carried out in which there were added to the poor solution1 precipitated ferric hydroxide freed from all adhering salts1 precipitated alumina1 shredded filter-paper1 absorbent cotton1 or carbon black4 ,in every case the same result was obtained as before1 a much improved growth of top and a vastly better root development4 ,since1 by no possibility could these various added substances have increased the concentration with respect to mineral nutrients1 another explanation must be sought4 ,aside from their insolubility1 the one property common to these various substances was the large amount of surface they brought into contact with the solution4 ,the one obvious explanation of their effects on the growth of the wheat seedlings1 therefore1 is that they withdrew or absorbed from the solution some substance or substances deleterious to plant growth4 ,as diluting with respect to mineral nutrients could not possibly be expected to improve the cultural value of the solution1 the conclusion seems evident that the effect produced by these various absorbents was due to more or less complete removal from the solution of organic substances inhibitory to plant growth4 ,these experiments were then repeated in a modified form by shaking the poor solution with such absorbents as precipitated ferric oxide or carbon black and filtering before adding the seedling plants4 ,the solutions thus prepared proved very satisfactory nutrient media1 although the decided elongation of the roots1 always observed when the absorbents were in contact with the solutions1 was not so noticeable with these filtered solutions4 ,the experiments just described were repeated with extracts from a number of soils which were supporting or had recently supported poor crops4 ,the accumulated mass of evidence admits of no doubt that in many cases the apparent lack of fertility of a soil is due to the presence of some organic substance or substances soluble in soil water4 ,this point established1 there was studied the effect of fertilizers when added to aqueous extracts from poor soils4 ,a large amount of experimenting has been done on this subject4 ,it has been found that the common commercial fertilizers1 as well as many other substances1 when added to the soil extract containing growing plants1 sometimes improve the plants1 sometimes the contrary4 ,but1 in general1 those particular substances which improve any given soil for a crop also improve the aqueous extract of the soil for the growth of the same crop plant3 i4 e41 should a soil be known to respond well to the application of superphosphates when planted to wheat1 then the probability is great that the aqueous extract of the soil will be improved as a culture medium for the wheat plant by addition of calcium phosphate4 ,particularly important in this connection are certain experiments with organic fertilizers4 ,a soil which had been found to be quite unproductive with regard to wheat and ordinary tame grasses yielded1 however1 a much better growth of plants if pyrogallol or better pyrogallol and lime were added to the soil some days before planting4 ,an aqueous extract of this soil tested with young wheat seedlings produced but a poor growth1 as did the soil itself4 ,but with the addition of pyrogallol or pyrogallol and lime to the soil extract1 and especially if the extract so treated were allowed to stand for a few days with free access of air1 there was obtained a culture medium which yielded remarkably good results with wheat seedlings4 ,not only was there an excellent and increased development of tops1 but the roots of the seedlings grown in the solution treated with pyrogallol were unusually long1 turgid1 clear and translucent4 ,here1 then1 there was obtained an increased amount and improved character of growth by the addition of a substance which contained only carbon1 hydrogen and oxygen1 and no recognized plant food4 ,other organic substances1 such for instance as tannin1 gave similar results4 ,with the recognition that the presence of organic dissolved substances in the nutrient medium produced effects on a growing plant of as great or even greater magnitude than those produced by inorganic dissolved substances1 there was carried out a number of experiments to test more specifically such substances as might reasonably be expected to be present naturally in soils4 ,the results thus obtained suggested experiments with other related substances4 ,the first substance to suggest itself is stable manure4 ,taking it all in all1 this substance is probably the most efficient as well as the most generally used soil amendment in the experience of mankind4 ,the good effects produced by this substance have in the past been generally considered as due to the readily 8available0 potash1 phosphoric acid and nitrogen it contains1 but thoughtful experimenters and agriculturists have long doubted that this explanation is sufficient1 since1 after all1 the mineral constituents of stable manure are usually small in amount1 and out of all proportion to the effects resulting from its use4 ,that some of the results are due to an improvement in the physical condition of the soil when manure is used has quite rightly been generally assumed2 but to its content of nitrogenous components its value has in the main been ascribed4 ,a well-fermented aqueous extract of stable manure was prepared1 and filtered free of suspended solids4 ,four equal volumes of this solution were taken4 ,three of these portions were evaporated to dryness in platinum dishes1 and the residues incinerated4 ,to the dishes containing3 the ash were added respectively nitric acid1 sulphuric acid1 and hydrochloric acid in slight excess1 and the dishes again brought to dryness4 ,water cultures for wheat seedlings were then prepared4#ajb ,into one was introduced the given volume of manure extract2 into another the ash from an equal volume of the extract which had subsequently been treated with nitric acid2 and cultures with the ash which had been treated respectively with sulphuric and hydrochloric acid were similarly prepared4 ,after ten days growth1 the plants from the several cultures were compared4 ,the plants from the cultures which contained the sulphates and the chlorides were not materially different from the plants grown in the check culture4 ,the plants from the nitrate culture had larger shoots1 but shorter roots than the check plants4 ,but the plants grown in the culture to which the manure extract had been added directly had by far larger and better shoots and the roots were incomparably superior to those grown in any other culture1 being larger1 thicker1 better branched1 clear1 bright and translucent1 and very turgid1 very like the roots obtained in cultures to which carbon black or precipitated ferric oxide had been added4 #ajb ,further studies on the properties of unproductive soils1 ,b4 ,e4 ,livingston et al41 ,bull4 #cf1 #aijg1 and #dh1 #aijh1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture4 ,the results of this experiment1 which has been repeated a number of times1 using manure extracts of various origins1 leave no doubt that it is the organic components of the manure which produce the characteristic effects1 for the ash culture contained all and even more of the mineral constituents 8available0 in the original extract1 and the nitrate culture excluded any explanation based on the nitrogenous content of the manure4 ,this conclusion was supported by the results of another experiment4 ,to a manure extract was added alcohol1 which precipitated most of the organic dissolved substances but very little of the inorganic ones4 ,the precipitated organic matter was filtered off1 dried carefully in a water oven to eliminate the alcohol1 and then taken up in sufficient water to equal the original volume of manure extract4 ,the nitrate containing the major part of the salts was boiled vigorously to eliminate the alcohol and water was then added to restore the original concentration4 ,a third solution was prepared by bringing together the organic and inorganic substances which had previously been separated as above described4 ,the three solutions were used as water cultures for wheat seedlings1 a solution of the original manure extract being taken for a check culture4 ,the original manure extract and the reconstructed manure extract gave plants of about equal development4 ,the culture containing the organic dissolved substances only1 gave plants of nearly1 but not quite1 equal development to those grown in the check culture4 ,but the plants grown in the solution containing the dissolved minerals only1 while fine plants and making what would ordinarily be considered a good development1 were decidedly smaller as regards their aerial parts1 and the roots were in no wise comparable to the roots of the plants grown in the cultures containing the dissolved organic substances4 ,this last experiment has been repeated1 with dissolved substances prepared from another manure extract1 but in this case the organic and inorganic substances were separated by dialysis4 ,this suggested yet another experiment1 in which it was sought to hasten the process of dialysis1 by introducing electrodes into the manure extract1 each electrode being surrounded by some porous membrane1 either of parchment paper1 or unglazed porcelain4 ,not only were the mineral constituents of the manure extract readily separated in this way1 passing into the electrode chambers1 as did also to some slight extent organic compounds1 but also about the outer walls of the electrode chambers there was marked segregation and deposition of organic materials4 ,the organic substances deposited at the cathode were found to stimulate greatly the growth of wheat seedlings while those deposited at the anode were found to retard the growth of seedlings4 ,it seems probable1 therefore1 that stable manure contains organic components which produce as great or greater effects upon growing plants as do the inorganic substances it contains3 that on the whole these organic components induce increased plant growth1 but some of them1 by themselves alone1 would retard plant growth4 ,in a similar way green manures have been examined4 ,if fresh clover1 alfalfa1 or cowpeas1 be macerated and an aqueous extract thus prepared1 it will in general be quite toxic to plants such as wheat2 and if this extract be allowed to stand and ferment or sour the resulting solution will be totally unfit for the growth of seedling plants4 ,but if the clover1 alfalfa1 or cowpea vines be allowed to wilt thoroughly before being macerated and extracted1 or if they be macerated and incorporated with soil and allowed to remain thus for ten days or a fortnight before being extracted2 then1 the resulting solution will be quite stimulating to such plants as wheat1 corn or the grasses1 when added either to water or soil cultures4 ,it would seem1 therefore1 that the mineral constituents of the legumes commonly employed as green manures are less important than the organic1 in affecting the growth of crops subsequently planted1 and the inhibitory or toxic action of fresh green manure seems to be recognized in the common practice of waiting some days after turning under a green manure crop before seeding to a new crop4 ,the wilting of a green manure involves a darkening and some blackening of the mass1 with apparently some absorption of oxygen4 ,this fact has suggested a trial of other organic substances which show a decided ability to absorb oxygen4 ,among such substances1 pyrogallol stands preminent4 ,it has been shown that when pyrogallol1 or better pyrogallol and lime1 is added to certain soils1 naturally low in productive power1 and allowed to stand for a few days1 these soils are readily brought into good condition and support good crops of wheat1 rye1 or grasses4 ,pyrogallol in water cultures is rather toxic to wheat plants1 even in quite dilute solutions4 ,but if the aqueous solution of pyrogallol be allowed to stand exposed to the air1 and better if the solution be made slightly alkaline as by the addition of lime1 oxygen is absorbed1 and a dark brown or blackened solution is soon formed1 which is stimulating to wheat seedlings4 ,many experiments have indicated it to be a general rule that soluble organic substances which are toxic to plant growth yield oxidation products which are harmless or positively beneficial4 ,the suggestion has been made that the well-known infertility of subsoils1 when freshly turned up1 is caused by the presence of alkaloids of the purine or codeine type1 due to the activities of anaerobic bacteria4 ,water cultures and pot cultures show that while these substances do have a marked effect on plant growth1 it is1 frequently1 quite beneficial2 strychnine for example1 in certain concentrations1 produces a very decided stimulation in the growth of wheat seedlings4 ,it is clear that some other explanation will have to be sought for the lack of fertility of subsoils4 ,a number of the substances which may be expected for one reason or another to be present in soils1 have been investigated as to their effect on plants4 ,in this connection may be cited the work of ,livingston#ajc and of ,dachnowski1#ajd who have studied the effect on vegetation of the organic substances dissolved in bog waters4 ,in the following table are given the results obtained by growing wheat seedlings in solutions containing some one of a number of substances which might be expected to occur in a soil or to be derivatives of such substances4 ,it will be observed that in the case of these dissolved organic substances1 as has been repeatedly established with the inorganic ones1 in concentrations sufficiently dilute not to be toxic1 they generally show the opposite effect and appear to be stimulating4 #ajc ,physiological ,properties of ,bog ,water1 by ,b4 ,e4 ,livingston1 ,bot4 gaz41 #ci1 #cdh-cee1 7#aije74 #ajd ,the toxic property of bog water and bog soil1 by ,alfred ,dachnowski1 ,bot4 gaz41 #df1 #acj-adc1 7#aijh74 ,,table ,i4--,,effect ,,of ,,various ,,organic ,,compounds ,,upon ,,the ,,growth ,,of ,,wheat ,,plants1 ,,with ,,especial ,,reference ,,to ,,their ,,toxic ,,properties#aje #aje ,certain organic constituents of soils in relation to soil fertility1 by ,oswald ,schreiner and ,howard ,s4 ,reed1 assisted by ,j4 ,j4 ,skinner1 ,bull4 ,no4 #dg1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijg4 ,,legend3 ,a ,duration of experiment ,b ,lowest concentration causing death ,c ,lowest concentration causing injury ,d ,concentration causing greatest stimulation ,compound ,a ,b ,c ,d ,remarks ---------------------------------------- ------------------------ daysp4p4m4p4p4m4p4p4m4 a ,aspartic acid #aj #ejj #ajj 4444 ,normal growth in ,,hooc4,,ch4,,ch7,,nh74,,cooh concentration below #ajj p4p4m4 ---------------------------------------- ------------------------ b ,asparagine #i ,no injury below ,,nh4,,oc4,,ch4,,ch7,,nh74,,cooh #a1jjj p4p4m4 ---------------------------------------- ------------------------ c ,glycocoll1 #i ,tops of all plants ,,ch7,,nh74,,cooh good4 ,roots slightly injured at higher concentrations ---------------------------------------- ------------------------ d ,alanine1 #aj 4444 #ejj #be ,only roots were ,,ch4,,ch7,,nh74,,cooh injured at #ejj p4p4m4 ---------------------------------------- ------------------------ e ,leucine #i 4444 4444 4444 ,no injurious action ,,ch47,,ch74,,ch7,,nh74,,cooh ---------------------------------------- ------------------------ f ,tyrosine1 #aa 4444 #aj ,,oh _/ ,c ,h ,,ch4,,ch7,,nh74,,cooh ---------------------------------------- ------------------------ g ,choline1 #aj #ejj #a ,roots affected more ,,ch,,ch,,oh than tops _/ 7,,ch7,n ,,oh ---------------------------------------- ------------------------ h ,neurine1 #i #bej #be ,,ch3,,ch _/ 7,,ch7,n ,,oh ---------------------------------------- ------------------------ ,neurine 7neutralized7 #h #bej #be ---------------------------------------- ------------------------ i ,betaine1 #i 444 444 ,no injury ,,ch4,,co _/ _/ 7,,ch7,n _/ _/ ,o ---------------------------------------- ------------------------ j ,alloxan1 #aj #a1jjj #ajj ,,nh4,,co _/ ,,co ,,co _/ ,,nh4,,co ---------------------------------------- ------------------------ k ,guanine1 #ab ,insoluble above #dj ,,nh4,c4,,nh4,,co4,c4,,nh p4p4m4 ,no harmful effects4 ,,ch _/_/ ,n--------,c4 ,n ---------------------------------------- ------------------------ l ,xanthine ,no injurious action4 ,,co4,,nh4,,co4,c4,,nh ,,ch _/_/ ,,nh----,c--,n ---------------------------------------- ------------------------ m ,guanadine1 #i #ajj #a ,,nh _/ ,,hn 3 ,c ,,nh ---------------------------------------- ------------------------ n ,skatol1 #i #bjj #ej ,roots injured more ,c4,,ch than tops _/ ,c,h ,,ch _/ ,,nh ---------------------------------------- ------------------------ o ,pyridine1 ,c,h,n #i 4444 #ej 4444 ,in solutions of #ej p4p4m4 and less the root growth was normal4 ---------------------------------------- ------------------------ ,picoline1 ,c,h,n4,,ch #g #a1jjj #ejj #ajj ---------------------------------------- ------------------------ ,piperidin #g #bej #be ,,ch ,h,c _/ ,,ch ,h,c _/ ,,ch ,,nh ---------------------------------------- ------------------------ ,piperidine #g #ajj #be #a 7neutralized7 ---------------------------------------- ------------------------ _/ _/ ,quinolin1 #f #ejj #e _/ _/ ,n ---------------------------------------- ------------------------ p ,ricin #aj #dj ,insoluble above #ej p4p4m4 ---------------------------------------- ------------------------ q ,mucin #aj #ajj ,not tested in concentrations higher than #ajj p4p4m4 ---------------------------------------- ------------------------ r ,pyrocatechin1 #ab #ejj #be #a ,c,h7,,oh77#a1b7 ---------------------------------------- ------------------------ s ,arbutin1 ,c,h,o #ab #ejj #be #a ---------------------------------------- ------------------------ t ,phloroglucin1 #ac #ejj #be #a ,c,h7,,oh77#a1c1e7 ---------------------------------------- ------------------------ u ,vanillin1 #i #ejj #a ,,cho _/ ,c,h----,o4,,ch ,,oh ---------------------------------------- ------------------------ ,vanillic acid1 #g #ajj #be #e ,,cooh _/ ,c,h--,o4,,ch ,,oh ---------------------------------------- ------------------------ v ,quinic acid1 #aj #ejj #ajj ,c,h7,,oh74,,cooh ---------------------------------------- ------------------------ ,o _/ w ,quinone1 ,c,h #i #ajj #a ,o ---------------------------------------- ------------------------- x ,cinnamic acid1 #h #ajj #be ,c,h,,ch 3 ,,ch4,,cooh ---------------------------------------- ------------------------ ,sodium cinnamate #ab 444 #ajj ,roots were stimulated in lower concentrations ---------------------------------------- ------------------------ y ,cumarin1 #h #ajj #a ,,ch3,,ch4,,co _/ _/ ,c,h_/ _/ #h #ajj #a _/ ,o ---------------------------------------- ------------------------ ,insoluble above z ,daphnetin #ab #ej #ej p4p4m4 ,roots somewhat injured ,,ch 3 ,,ch4,,co _/ _/ ,c,h ------ ,o 7,,oh7 ---------------------------------------- ----------------------- aa ,esculin1 ,c,h,o #ac #ejj #a ---------------------------------------- ----------------------- bb ,piperonal 7heliotropine7-- ,,cho _/ ,c,h----,o ,o----,,ch #g #ajj #a 444 ---------------------------------------- ------------------------- cc ,borneol1 ,c,h7,,oh7 #aj #ajj #a 444 dd ,camphor1 ,c,h,o #h #cjj #e 444 ee ,turpentine1 ,c,h #h #ejj #aj 444 ---------------------------------------- ------------------------- a4 ,aspartic acid has been found in young sugar-cane and in seedlings of the bean and pumpkin4 b4 ,asparagine was first found in asparagus2 but has since been shown to be relatively abundant in many species4 c4 ,glycocoll is one of the simpler and more common degradation products of proteins4 d4 ,alanine is a common degradation product of proteins and is related chemically to phenylalanine1 and to tyrosine1 which has been found in many plants4 e4 ,leucine1 an amino-acid of a paraffine series and a decomposition product of proteids1 has been found in certain mushrooms1 vetches1 lupine1 gourds1 potatoes1 corn1 etc4 f4 ,tyrosine is an important decomposition product of proteids1 is widely distributed and found in many plants and fungi4 g4 ,choline is a derivative of certain lecithins and is found in many seeds and growing plants4 h4 ,neurine is a substance closely related to choline1 and probably formed from it4 i4 ,betaine is closely related to both choline and neurine1 and is found in many seeds and plants4 j4 ,alloxan is closely related chemically to convicine1 which latter is found in beets and certain beans4 k4 ,guanine is a widely distributed nitrogenous body1 and has been found in the seeds of vetch1 alfalfa1 clover1 gourds1 barley1 sugar-beets and sugar-cane4 l4 ,xanthine1 a substance closely related to guanine1 has been found in a number of plants4 m4 ,guanidine1 a substance chemically related to guanine1 has been found in a number of plants of different species4 n4 ,skatol is a derivative of proteids and is a common product of the activities of some varieties of bacteria4 o4 ,pyridine has been shown to exist in soils1 as such probably1 by ,shorey1 who obtained it from certain soils in ,hawaii4 p4 ,ricin is found in the castor-oil plant4 q4 ,mucin has been found in yams4 r4 ,pyrocatechin has been found in the bark of various trees1 the berries of the ,virginia creeper1 the sap of sugar-beets and in several varieties of willows4 s4 ,arbutin has been found in many plants1 especially in some of the grasses4 t4 ,phloroglucin is easily derived from a number of plant constituents4 u4 ,vanillin forms readily from a glucoside1 which is very widely distributed in many plants1 and by some authorities is supposed to be a product of the decomposition of wood tissues4 v4 ,quinic acid1 which is found with quinine in the cinchona bark1 also occurs in beet leaves1 certain hays1 cranberry leaves1 and occasionally in other plants4 w4 ,quinone has been shown to result from the action of a certain fungus1 ,streptothrix chromogena1 common in soils4 x4 ,cinnamic acid is found in certain barks1 and forms esters which have been found in the leaves of various plants4 y4 ,cumarin has been found in a large number of plants1 including the grasses1 beets1 sweet clover1 etc4 z4 ,daphnetin occurs in some species of ,daphne and is closely related to cumarin4 aa4 ,esculin1 as well as the corresponding esculetin1 has been found occasionally in a number of plants4 bb4 ,heliotropine1 or piperonal1 has the odor of heliotrope and is found in flowers4 cc4 ,borneol occurs in needles of different varieties of pine1 fir1 spruce and hemlock1 golden rod and thyme4 dd4 ,camphor is closely related chemically to borneol and is secreted by a number of plants2 it is found in the wood of ,cinnamomum1 cinnamon root1 in the leaves of sassafras1 spikenard1 rosemary1 rosewood1 etc4 ee4 ,turpentine is a constituent of many plants and coniferous trees4 ,finally1 a number of organic substances has been isolated from soils4 ,their composition1 and in several cases their constitutions have been determined4 ,the effects of these on plants1 when they are present in the cultural media have been studied4 ,thus1 ,shorey#ajf was able to isolate picoline carboxylic acid 7,c,h,,no7 from certain soils in ,hawaii1 and this same substance has since been found in several soils of the ,united ,states4 ,in aqueous solutions it is quite toxic to wheat seedlings4 ,since then a number of other definite organic compounds have been isolated from soils belonging to at least eight different classes of organic substances1 including3#ajg ,hentriacontane1 ,c,h4 ,monohydroxystearic acid1 ,,ch7,,ch7,,choh7,,ch7,,cooh4 ,dihydroxystearic acid1 ,,ch7,,ch7,,choh4,,choh47,,ch7 ,,cooh4 ,agroceric acid1 ,c,h,o4 ,paraffinic acid1 ,c,h,o4 ,lignoceric acid1 ,c,h,o4 ,phytosterol1 ,c,h,o4,h,o4 ,pentosan1 ,c,h,o4 ,agrosterol1 ,c,h,o4,h#j4 ,picoline carboxylic acid1 ,c,h,o,n4 ,histidine1 ,c,h,o,n4 ,arginine1 ,c,h,o1,n4 ,cytosine1 ,c,h,,on4,h,o4 ,xanthine1 ,c,h,o,n4 ,hypoxanthine1 ,c,h,,on4 ,glycerides1 resin acids1 etc4 #ajf ,organic nitrogen in ,hawaiian soils1 by ,e4 ,c4 ,shorey1 report of ,hawaii ,experiment ,station1 #aijf1 #cg-ei4 #ajg ,chemical ,nature of ,soil ,organic ,matter1 by ,oswald ,schreiner and ,edmund ,c4 ,shorey1 ,bull4 #gd1 ,bureau of ,soils1 ,u4 ,s4 ,department of ,agriculture1 #aiaj4 ,some of these1 picoline carboxylic acid1 dihydroxystearic acid and the pentosan just cited1 are toxic to growing plants2 others are not4 ,the origin and mode of production of these substances in the soil is1 generally speaking1 uncertain and obscure1 and is yet one of the important fundamental problems confronting the soil chemist4 ,it is important to note that the organic substances thus far isolated from soils are of widely varying types1 and with very different chemical characteristics4 ,as pointed out above1 almost any type of organic substance is likely to be found in soils1 and the effects of any of them on growing plants can hardly be predicted from a priori considerations4 ,it has been found that as a general rule the continued growth of one crop in any soil results in a low crop production4 ,pot cultures have given even more pronounced results in the same direction4 ,the explanation long accepted is that the soil has1 as a result of continued cropping1 become deficient in some one or more of the 8available0 mineral nutrients4 ,pot experiments1 where the garnered crop was returned to the soil and still a diminished yield was obtained1 throw doubt on this explanation4 ,still further doubt results from water-cultures which1 by growing a crop in them1 become 8poor0 for subsequent crops1 although there is maintained in them an ample supply of mineral plant nutrients1 and they are easily renovated by good absorbers4 ,these facts find a more satisfactory explanation as being due to the production in the nutrient medium of deleterious organic substances originating in the growing plant itself4 ,this idea seems to have been advanced first by ,de ,candolle1 in #ahcb1ajh to account for the beneficial results obtained by employing a rotation of crops4 ,it appears to have been held by ,liebig at one time1 although he subsequently abandoned it in favor of the view that the benefits of a crop rotation are due to the several crops requiring different proportions of mineral nutrients1 and that the disturbance of the balance in the soil produced by one crop is not unfavorable to the growth of some other crop4 ,although lacking direct experimental confirmation1 this latter view of ,liebig's has long prevailed among agricultural investigators1 partly by reason of his authority1 partly by reason of the dominance of the plant-food theory of fertilizers1 and partly by reason of the fact that the ideas of ,de ,candolle as originally advanced included certain errors soon detected4 ,the trend of recent investigations has been distinctly in favor of a modified form of the view of ,de ,candolle4 ,it has been recognized that other factors enter into crop rotations1 such as the elimination of associated weeds1 various kinds of animal1 insect and plant parasites1 preparation of the soil by a deep-rooted crop for a shallow-rooted following crop1 etc4 ,it has come to be recognized that there are natural associations of plants1 and natural rotations of vegetation certainly determined by other than plant food factors4 ,thus1 in the eastern ,united ,states1 wheat is followed by ragweed naturally1 while across the fence cocklebur and wild sunflower come in after the corn1 the difference in vegetation being as sharply marked after the removal of the crops as when they still occupied the land4 ,analyses of the ragweed1 for instance1 although it is a shallower rooted crop than wheat1 show that it takes from the soil as much of the mineral nutrients as does the preceding#aji wheat crop4 ,the investigation of ,lawes and ,gilbert#aaj on fairy rings showed that the continual widening of the rings can not be satisfactorily explained by the comparison of the mineral constituents in the soil within and without the rings4 ,work at ,woburn#aaa on the effect of grass on apple trees finds no other plausible explanation than that the growing grass produces in the soil organic substances detrimental to young apple trees4 ,a number of similar cases have been recorded4 #ajh ,see in this connection1 ,further studies on the properties of unproductive soils1 by ,b4 ,e4 ,livingston1 ,bull4 ,no4 #cf1 ,bureau of soils1 ,dept4 of ,agric41 #aijg1 p4 #g-i4 #aji ,mr4 ,j4 ,g4 ,smith has made a comparison between the potash and phosphoric acid content of the wheat and following crop of ragweed grown on a farm in ,fairfax ,co41 ,va4 ,his unpublished results1 with some others found in the literature1 are given in the following table3 ,potash,phosphoric ,material ,k,o acid1 ,p,o ,analyst ---------------------------------------- ------------------------- ,wheat #j4gf #j4eb ,smith ,young ragweed #a4gh #j4gc ,smith ,ragweed in seed #a4bh #j4ce ,smith ,ragweed in seed and accompanying plants #a4ah #j4ci ,smith ,winter wheat in flower #a4gif #j4ea ,wolff's tables in ,johnson's 8,how ,crops ,grow10 p4 #cgf4 ,ragweed #a4gi #j4da ,de,roode1in ,bull4 #ai1 ,w4 ,va4 ,agr4 ,exp4 ,sta41 #ahia ,ragweed #a4hji #j4ed ,burney1 #b;d4 ,ann4 rept4 ,s4 ,c4 ,stat41 #ahhi1 p4 #adf ---------------------------------------- ------------------------- ,on the whole1 ragweed seems to require and take from the soil about as much mineral matter as does wheat4 ,it is stated by some of the dairy farmers near ,washington1 who cut the mixture of ragweed1 other weeds and grass following wheat1 for a hay crop1 that the weight of the ragweed crop is generally heavier than that of the wheat crop4 ,therefore the ragweed actually removes more mineral matter from the field than does the wheat4 ,these facts lend no support to the popular notion that wheat 8exhausts0 the soil of its 8available0 mineral plant nutrients4 ,for analyses of a number of common ,american weeds1 see ,analyses of the ashes of certain weeds1 by ,francis ,p4 ,dunnington3 ,am4 ,chem4 ,jour41 #b1 #bd-bg1 7#ahhj74 #aaj ,note on the occurrence of 8fairy rings10 by ,j4 ,h4 ,gilbert3 ,jour4 ,linn4 ,soc1 #ae1 #ag-bd1 7#ahge74 #aaa ,second1 third and fifth reports of the ,woburn ,experimental ,fruit ,farm1 #aijj1 #aijc1 #aije4 ,finally1 although less work has been done in this direction with higher plants than with other organisms1 it is now recognized as a general law of all living organisms that they function less readily as the products of their activities accumulate4#aab ,these products may1 however1 be inimical1 neutral or even stimulating to other organisms4 #aab ,it may not be amiss to point out here that this general law holds for all dynamic phenomena4 ,in chemistry1 for instance1 the general law is well recognized that the rate of reaction diminishes with increase in the active mass of the reaction products4 ,it can be shown that the principle applies to plant growth4 ,young plants will withdraw potassium more rapidly than chlorine from solutions of potassium chloride2 that is1 the solution soon contains free hydrochloric acid4 ,conversely the plants cause a solution of sodium nitrate to become alkaline4 ,therefore1 if the above principle holds1 then the initial addition of small amounts of hydrochloric acid to a solution of potassium chloride should slow up the absorption of potassium by seedling wheat plants1 or the addition of sodium hydroxide the absorption of nitrogen from a solution of sodium nitrate4 ,mr4 ,j4 ,j4 ,skinner has tested this idea with the following results1 growing carefully selected wheat seedlings1 for #c days in solutions of pure potassium chloride1 solutions of potassium chloride containing initially enough excess of hydrochloric acid to be of an ,n_/1 concentration with respect to the acid1 solutions of sodium nitrate1 and solutions of sodium nitrate containing initially an excess of sodium hydroxide4 ,solutions of ,k,cl containing #hj p4p4m4 ,k,o4 #a ,k,o absorbed #dj4j p4p4m4 #b ,k,o absorbed #dj4j p4p4m4 #c ,k,o absorbed #cf4c p4p4m4 ,solutions of ,k,cl 7#hj p4p4m4 ,k,o7 and ,h,cl 7,n_/174 #d ,k,o absorbed #bf4g p4p4m4 #e ,k,o absorbed #bi4e p4p4m4 #f ,k,o absorbed #bf4g p4p4m4 ,solutions of ,na,n,o containing #hj p4p4m4 ,,nh4 #g ,,nh absorbed #cj4b p4p4m4 ,s ,,nh absorbed #cj4b p4p4m4 #i ,,nh absorbed #cb4e p4p4m4 ,solutions of ,na,n,o 7#hj p4p4m4 ,,nh7 and ,na,o,h 7,n_/174 #aj ,,nh absorbed #bg4h p4p4m4 #aa ,,nh absorbed #cd4c p4p4m4 #ab ,,nh absorbed #bg4h p4p4m4 ,this problem has been investigated critically by direct experimentation1 growing wheat1 and other seedlings in water and agar cultures4#aac ,it has been shown that wheat renders the culture media unsuitable for subsequent wheat crops1 though it can be reclaimed or renovated by treatment with such absorbents as carbon black1 or by other methods4#aad ,wheat did about as well when grown in a medium which had previously supported a growth of cowpeas as when planted in a fresh medium2 poorer results were obtained after oats2 no crop produced such poor results in the succeeding wheat crop as did wheat itself4 #aac ,some factors in soil fertility1 by ,oswald ,schreiner and ,howard ,s4 ,reed1 ,bull4 ,no4 #dj1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijg4 #aad ,soil fatigue caused by organic compounds1 by ,oswald ,schreiner and ,m4 ,x4 ,sullivan3 ,jour4 ,biol4 ,chem41 #f1 #ci-ej1 7#aiji74 ,it is yet a matter of dispute as to whether the substances thus added to nutrient media are truly excretory products of the plant1 sloughed off or otherwise eliminated from the surface of the roots1 or further elaborated by bacterial or other agencies before becoming effective4 ,these are important problems for the plant physiologist and the soil chemist alike4 ,it is beyond dispute1 however1 by reason of a large and increasing weight of evidence1 much of it direct experiment1 that1 as a result of the growing of plants1 soils and the soil water do contain organic substances2 harmful to the plant or organism eliminating them2 harmful1 innocuous1 or even stimulating to other plants or organisms4 ,for the elimination from the soil of toxic or inhibitory organic substances1 whether excreted by roots or otherwise produced1 several methods are more or less effective4 ,when1 as is sometimes the case1 the substance is volatile1 it may be removed by heating1 distilling with steam1 or passing a current of air through the soil or cultural medium4 ,these methods1 while effective in the laboratory and possibly applicable to greenhouse conditions1 are naturally inapplicable to field conditions4 ,in this last case the obvious procedure is to increase as much as possible the absorptive powers of the soil2 to secure the best possible drainage2 and with these1 the best possible aeration of the soil4 ,it has been found that1 in general1 a cultural medium which has been rendered unfit for the continued growth of a crop1 is readily renovated by treatment with oxidizing agents1 and is sometimes rendered even better than ever by such treatment1 which would suggest that the oxidation products from plant effluvia may be even beneficial to the plant4 ,to this end the growing plant seems itself to be an active agent1 apparently attempting automatically to protect itself against the products of its own activities4 ,it has been pointed out by ,molisch#aae that root secretions have an oxidizing power1 apparently of an enzymotic character4 ,some doubt of the validity of ,molisch's work has been raised by ,czapek1 ,pfeffer1 and others2 nevertheless it is now accepted that while intercellular autoxidation or reduction processes may take place in living roots1 the higher plants1 such as our common crop plants1 also show a more or less well-developed extracellular oxidizing power in the neighborhood of the root tips and root hairs4#aaf ,that this oxidizing power displayed by growing roots is enzymotic is indicated by the fact that artificial culture media frequently display it also after plants have been grown in them for a short while4#aag #aae ber ,wurzelausscheidungen und deren ,einwirkung auf organische ,substanzen1 von ,hans ,molisch4 ,sitzungsber4 ,akad4 ,wiss4 ,wien1 ,math4 nat4 ,k#a41 #if1 #hd-aji 7#ahhh74 #aaf ,the rle of oxidation in soil fertility1 by ,oswald ,schreiner and ,howard ,s4 ,reed3 ,bull4 ,no4 #ef1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aiji4 #aag ,from considerations as yet highly speculative1 a different type of oxidation by roots might be anticipated4 ,it is recognized that in the absorption of mineral nutrients by plants a certain amount of selection enters4 ,for example1 a plant with its roots in a solution of potassium chloride1 absorbs more potassium than chlorine1 relatively1 and free hydrochloric acid is left in the solution4 ,obviously in the absorption1 work is done1 and a possible explanation is that water is decomposed at the absorbing surface of the root1 with the liberation of oxygen4 ,theoretically1 it ought not to be difficult to investigate this by a study of the energy changes during absorption1 but growing plants do not lend themselves readily to such experimentation4 ,it has been shown that the oxidizing action of growing roots is generally promoted by having the cultural medium slightly alkaline or neutral rather than acid4 ,it is also promoted by the addition of various mineral salts1 notably by nitrates1 phosphates1 or lime salts4 ,potassium salts promote the oxidation but slightly1 and in some experiments have even produced a slight decrease4 ,the corresponding sodium and ammonium salts are more favorable than those of potassium4#aah ,it appears altogether probable1 therefore1 that the mineral salts in commercial fertilizers may have some importance in this connection4 ,whatever may be the role of mineral fertilizers towards organic substances toxic to growing plants1 it is certain that they have an importance and one that is probably specific1 as indicated by some recent investigations4#aai ,culture solutions containing the constituents potassium1 nitric acid and phosphoric acid were prepared in such manner that they covered the range of all possible ratios of these constituents in intervals of ten per cent4 in each4 ,into one set of these solutions was introduced dihydroxystearic acid1 into another set cumarin1 and into a third set1 vanillin1 and into a fourth set1 quinone4 ,the growth of wheat seedlings in these several sets showed indubitably that these several organic substances which are all deterrent to the growth of wheat1 were modified in their influence by the presence of the mineral salts2 but that nitrates were more efficient than the other minerals in the case of the solutions containing dihydroxystearic acid or vanillin2 phosphates were most efficient in the case of the solutions containing cumarin1 and potassium most efficient in solutions containing quinone4 ,as the organic substances used in these experiments1 either in themselves or as typifying classes of compounds1 may be anticipated in soils under natural conditions1 it is again apparent that mineral fertilizers have a function in addition to the traditional one of increasing the supply of mineral nutrients4 #aah ,action of fertilizing salts on plant enzymes1 by ,m4 ,x4 ,sullivan1 ,jour4 biol4 chem41 #f1 7#aiji71 proceed4 ,,xliv4 #aai ,private communication by ,dr4 ,oswald ,schreiner and ,mr4 ,j4 ,j4 ,skinner4 ,the fact that the oxidizing power of roots is more marked when grown in aqueous extracts of soils in good tilth than in extracts made from soils in poor tilth1 shows that cultural methods are no less important in field practice than are fertilizers in promoting this important activity of plants4 ,there is little reason to doubt that oxidizing agencies other than plant roots 7bacterial for instance7 are more or less active in every arable soil1 and numerous investigations1 among which ,russell's researches#abj are conspicuous1 leave little doubt that oxidation processes are promoted by good tilth4 ,it is apparent1 therefore1 that by the activities of the plant itself as well as other agencies1 the general tendency in soils is the destruction of or rendering innocuous harmful plant effluvia or other organic substances1 and to this end are effective each of the three methods of soil control generally practiced1 namely1 tillage1 crop rotation and fertilizers4 ,among the organic components of the soil none have greater importance and interest than those containing nitrogen or as they are frequently called the nitrogen carriers4 ,conspicuous among these are the nitrates4 ,while it is now generally conceded that ammonia and other nitrogen compounds can be taken up by higher plants and elaborated by them under special conditions1 it nevertheless remains true that plants draw their needed supplies of nitrogen from the soil solution1 mainly in the form of nitrates4 ,the problems presented by these nitrogen carriers are mainly bacterial#aba and physiological1 but certain features are of direct importance to the soil chemist and to a study of the soil solution4 ,it is now known generally that there are many kinds of nitrifying and denitrifying bacteria in soils1 and that probably every arable soil contains several species1 or varieties at least of both kinds4 ,with good tilth and consequent aerobic conditions1 nitrifying processes prevail1 and with poor tilth or in subsoils1 anaerobic conditions and denitrifying processes prevail4 ,warmth1 moisture1 the reaction of the soil1 and perhaps other factors markedly affect the activity of the organisms of the soil solution4 ,another important factor is that the absorptive powers of the higher plants are markedly affected by sunlight1 so that1 especially on bright and clear days1 there is generally a higher concentration of nitrates in the soil solution in the morning than in the evening4 ,this fact would seem to affect seriously the value of some recent and extensive investigations where it has been sought to classify soils by their content of water-dissolved nitrates4 ,nitric acid is more readily leached from soils than are most other acid radicals4 ,consequently nitrates1 like other organic components of the soil solution1 and unlike inorganic components1 tend to vary greatly in concentration4 #abj ,oxidation in soils1 and its connection with fertility1 by ,edward ,j4 ,russell3 ,jour4 ,agric4 ,sci41 ,i1 #bfa-bgi1 7#aije72 ,pt4 ,,ii4 ,the influence of partial sterilization1 by ,francis ,v4 ,darbishire and ,edward ,j4 ,russell1 #b1 #cje-cbf1 7#aijg74 #aba ,the fixation of atmospheric nitrogen by bacteria1 by ,j4 ,g4 ,lipman1 ,bull4 #ha1 ,bureau of ,chemistry1 ,u4 ,s4 ,dept4 of ,agriculture1 #aijd1 p4 #adf-afj2 ,a review of investigations in soil bacteriology1 by ,edward ,b4 ,voorhees and ,jacob ,g4 ,lipman1 ,bull1 #aid1 ,office of ,experiment ,stations1 ,u4 ,s4 ,dept4 of ,agriculture1 #aijg4 ,chapter ,,xii4 ,,fertilizers4 ,it is generally recognized that the great practical problem confronting the soil chemist is the proper use of soil amendments or fertilizers4 ,the farmers of the ,united ,states now spend annually for fertilizers upwards of #ajj1jjj1jjj4 ,it is estimated by various authorities that a large fraction1 perhaps as much as three-fourths1 of the material represented by this expenditure is misapplied for lack of intelligent direction4 ,yet all of this enormous mass of fertilizers can be used to advantage4 ,great as it is1 it is relatively small beside the total which will1 and must1 be used in a not distant future1 with the growth and development of intensive methods of cultivation consequent upon the rapid settling of the country1 the practical disappearance of new lands and the increase in money value of the old lands4 ,the commercial importance of the problem1 therefore1 makes it desirable that special emphasis should be given to fertilizers from the point of view developed in the preceding chapters4 ,it should be recalled that the use of fertilizers constitutes one of the three great general methods of soil control1 and further that while tillage methods1 crop rotations1 and fertilizer applications can be used to supplement one another1 no one of these methods can be expected to take satisfactorily the place of another4 ,crop production is dependent upon a large number of factors4 ,upon the rainfall1 both as to the amount and distribution2 upon the sunlight1 as to amount and distribution2 upon the chemical and physical properties of the soil2 soil bacteria and other biologic agents2 enzymes in the soil2 biological factors in the plant1 and probably many other things4 ,opinions do and will continue to differ as to what these factors are1 but at least every one agrees that they are many4 ,attempting to formulate these factors develops fundamental difficulties1 since it is not positively known how far the variables are dependent or independent1 and we have no idea as to the nature of the function or functions4 ,the weight of existing evidence favors the view that all the factors are dependent variables1 although numerous attempts have been made from time to time to show that some one factor1 such as the rainfall for instance1 or the mean annual temperature1 or available plant-food1 is practically an independent factor4 ,although it should be rather easy to determine experimentally the nature of the function1 if any of these various factors were independent1 this has never been done1 and this fact is itself a strong argument that all the factors in crop production are dependent on one another4 ,when there is introduced into the equation a factor for any one of the methods of soil control1 i4 e41 tillage1 crop rotation1 or fertilizers1 it becomes even more apparent that the function is determined by dependent variables1 for the new factor always more or less affects several if not all of those already cited4 ,for instance1 fertilizers certainly affect the chemical properties of the soil1 its physical properties1 the soil bacteria1 perhaps the plant-food supply1 the oxidation of plant effluvia and other factors4 ,it is obvious1 therefore1 that a satisfactory theory of fertilizer action can not be a simple one but must of necessity be complex2 and the same statement is no less true as regards tillage and crop rotation4 ,the recognition of the fact that the action of fertilizers is a complex function depending upon many factors and groups of factors which vary among themselves and with each individual soil1 carries with it the conviction that an exact or quantitative fertilizer practice1 while theoretically possible1 is probably unattainable since methods for the solution of such complex functions are generally wanting4 ,it is not surprising1 therefore1 that the empirical experience of the past has failed to develop a quantitative practice4 ,however disappointing this may seem at first sight1 the prospect is not altogether hopeless1 for this point of view indicates a systematic scheme for experimentally determining a qualitative1 but nevertheless rational1 fertilizer practice4 ,the dominance of the plant-food theory of fertilizers in the past1 shutting off1 as it has1 a rational attack of the problem1 is causing the annual waste of millions of dollars in misapplied fertilizers1 and it is of scarcely less economic than scientific importance to investigate and extend our knowledge of the effect of soil amendments upon the many factors in crop production4 ,with a knowledge of the effect of fertilizers upon the physical1 chemical and biological factors in crop production1 and of the nature of the interdependence of these factors1 will come the ability to manage intelligently the individual field for the particular crop4 ,this knowledge can only come by attacking the problem from the dynamic viewpoint1 and so far as the soil factors are concerned1 they can apparently be studied best as they affect the properties of the soil solution4 ,while it seems certain that some fertilizer effects are directly upon the soil and secondarily upon the plants1 it cannot be doubted that in others1 the phenomena are more directly concerned with the absorption by and the metabolism within the plant and until these plant processes are better understood1 nothing approaching a satisfactory practice can be anticipated4 ,why and how plants exercise the selective powers they appear to possess are fundamental questions yet to be answered4 ,the important effects sometimes produced by adding to the nutrient medium such substances as manganese salts which are not necessary to the growth of the plant1 can no more be neglected than the study of the phosphorus needs4 ,the presence in the soil universally of substances other than the recognized mineral nutrients1#abb may very well have a significance for plant production hitherto unsuspected1 for the fact that an organism can continue to function in the absence of a substance is no argument1 much less proof1 that it would not function better with that substance present4 ,recent investigations1 showing that animal organisms are sometimes more resistant to certain toxins and diseases under starvation conditions or when ingesting substances unnecessary to normal development1 suggest the possibility at least of similar phenomena with plants4 ,it is at any rate clear that the practical problem of the best production of plants from soils is not merely one of providing a relatively large supply of potassium1 phosphorus and nitrogen4 #abb ,see1 for instance1 ,barium in soils1 by ,g4 ,h4 ,failyer1 ,bull4 ,no4 #ga1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 of ,agriculture1 #aiaj4 ,in this connection it is well to consider what constitutes a commercial fertilizer4 ,it must be a substance the addition of which either directly or indirectly affects the properties of the soil or the growing plant2 it must be obtainable in large quantities and from a source or sources of supply not readily exhausted2 and it must be cheap4 ,of the many substances filling the first condition1 all those which fulfill also the other conditions are used as fertilizers1 with the exception of common salt and human excrement4 ,in spite of the fact that it does not contain a conventional plant-food1 sodium chloride appears to produce results quite similar to those produced by the usual fertilizer salts4 ,its use has been followed generally by an increased yield of crop1 but occasionally by a decreased one1 and it appears not improbable that further investigation would show sodium chloride to have a considerable value as a fertilizer4 ,human excrement or night soil1 and the sewage and garbage refuse of our large cities are not commercial fertilizers1 although having undoubtedly a high agricultural value4 ,objection has been urged to them that they are 8filthy0 and liable to contain dangerous pathogenic organisms4 ,both objections could be met4 ,it seems a more rational explanation that the agricultural methods of this country have not yet become sufficiently intensive to necessitate the conservation of such materials or to justify their commercial exploitation4 ,new products will come into use from time to time1 as in the case of calcium cyanamid and basic calcium nitrate4 ,but it is worthy of note that these substances have become available not so much because of their agricultural value1 but incidentally to the efforts of inventors and manufacturers to produce cheap nitric acid for the preparation of high explosives4#abc ,there seems no reason to doubt that an ample supply of desirable substances will always be available for fertilizer purposes4 ,the immediate practical problem for the future is not the seeking of new fertilizers but the rational use of those at hand4 #abc ,in this connection it may be of interest to call attention to the fact that the ,twelfth ,census shows less than a fifth of the sodium nitrate brought into the ,united ,states goes into the fertilizer trade4 ,moreover1 the production of ammonium salts by the extensive coke and gas plants of the country has been practically nil not because of any inherent difficulties in making them or because the cost of production has been high1 but because the market demands in this country have been too small4 ,chapter ,,xiii4 ,,alkali4 ,in the preceding chapters there have been considered the phenomena which obtain under humid conditions4 ,under exceptional conditions of prolonged drought there occurs an accumulation of soluble mineral substances at or near the surface of the soil4 ,this phenomenon is pronounced in arid and semi-arid regions1#abd and the accumulations of soluble salts occurring in such regions is known in the ,united ,states as 8alkali10 in ,india as 8reh10 in ,africa as 8brak10 and in other countries by various local designations4 ,the study of the extreme conditions producing alkali has added materially to the present knowledge of the processes taking place in soil of humid areas4 ,moreover1 alkali-infested areas are themselves becoming of so much importance with the growing needs for further new lands1 that it seems wise to give here an outline of the chemical principles involved in their soil solutions4#abe ,alkali is sometimes a single salt1 but usually a mixture of some two or more of the chlorides1 sulphates1 carbonates1 bicarbonates1 and occasionally the nitrates1 phosphates and borates1 of sodium1 magnesium1 potassium1 and calcium1 and occasionally strontium and lithium4 ,in the ,united ,states1 when the carbonate of sodium is present to an appreciable extent1 the salt mixture is known as black alkali1 in contradistinction to white alkali1 which latter does not contain sodium carbonate4#abf ,generally1 but not always1 soils containing alkali also contain accumulations of the less soluble salts1 calcium carbonate1 or calcium sulphate1 or a mixture of the two4 ,these substances1 sometimes cementing the less soluble mineral components of the soil1 sometimes almost pure1 are found in layers more or less continuous1 and from a fraction of an inch to several feet in thickness1 in a position approximately parallel to and at a moderate depth below the surface of the soil4 ,in such cases these layers form a 8hard-pan0 and frequently the treatment of this type of hard-pan is the most difficult and vexing problem in the management of alkali-bearing soils4 #abd ,occasional occurrence of alkali in humid regions1 by ,frank ,k4 ,cameron1 ,bull4 ,no4 #ag1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aija1 p4 #cf-ch4 ,this phenomenon should not be confused with the surface deposition of various kinds of saline material from springs1 which is fairly common in both humid and arid regions1 the world over4 #abe ,alkali soils of the ,united ,states1 by ,clarence ,w4 ,dorsey1 ,bull4 ,no4 #ce1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijf4 #abf ,black alkali is so called because the caustic solution containing sodium carbonate1 in rising to the surface of the soil1 dissolves and carries with it organic matter which is subsequently left on the surface in more or less blackish deposits1 often ring-like in appearance4 ,it is by no means uncommon1 however1 to find deposits of 8black alkali0 which are not black at all1 and it is quite common to find 8white alkali0 so dark in color as to suggest the presence of sodium carbonate1 although the latter be absent4 ,the origin of alkali is often uncertain4 ,in some cases the geological evidences in the area make it certain that the alkali came from the desiccation of former bodies of sea water which had become isolated from the ocean4 ,in other cases the alkali appears to come from the desiccation of lakes which are the depositories of the drainage of a surrounding area1 and which have no outlet to the sea4 ,in still other cases it has been supposed that the alkali is derived from wind-borne sea-spray4 ,various explanations of a more or less special character with regard to particular localities or circumstances are to be found in the literature4#abg ,the chemical principles involved in the desiccation of a body of sea water are now pretty well understood1 owing mainly to the investigations of van't ,hoff1 ,meyerhoffer1 and their coworkers4#abh ,the salts in sea water and those constituting 8white alkali0 are mainly the chlorides and sulphates of sodium1 potassium and magnesium4 ,calcium is also present1 appearing in deep deposits as anhydrite1 and at the surface as gypsum4 #abg ,an interesting case is the ,billings ,area1 ,montana1 where the alkali seems to be derived from the oxidation1 solution and subsequent hydrolysis of the pyrites and marcasite of the neighboring ,pierre shales4 ,the sulphuric acid thus formed1 leaching through shales and sandstones1 takes up various bases and the predominating salts in the alkali of this area are the sulphates of sodium and magnesium4 #abh ,zur ,bildung der ozeanischen ,salzablagerungen1 von ,j4 ,h4 van't ,hoff1 ,braunschweig1 #aije-ji4 ,for a detailed discussion of these results with reference to alkali deposits see3 ,calcium sulphate in aqueous solutions1 by ,frank ,k4 ,cameron and ,james ,m4 ,bell1 ,bull4 ,no4 #cc1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijf4 ,from the results of this work it is possible to predict the order in which the different salts or minerals will separate from the evaporating solution4 ,at ordinary temperature 7#be ,c7 the first salt to be deposited from the dilute solution is gypsum 7,ca,s,o4#b;,h,o7 followed by halite or sodium chloride 7,na,cl7 in quantity4 ,sodium chloride continues to separate at all higher concentrations4 ,next will be deposited kainite 7,mg,s,o,k,cl4#c;,h,o74 ,at the concentration then reached1 the stable sulphate of calcium is anhydrite 7,ca,s,o71 which continues to separate from solution as desiccation proceeds4 ,consequently1 if the gypsum previously deposited is yet in contact with the solution1 it tends to be transformed to anhydrite and at all higher concentrations the deposition of anhydrite may be expected4 ,as evaporation proceeds a point is reached where kainite and kieserite 7,mg,s,o4,h,o7 separate4 ,further evaporation brings a concentration at which kieserite and carnallite 7,mg,cl4,k,cl4#f;,h,o7 are precipitated1 and as the process proceeds1 finally the point is reached where kieserite1 carnallite and bischofite 7,mg,cl4#f;,h,o7 all three separate with sodium chloride4 ,the final products separating at a higher temperature1 #hc ,c41 are the same four solids1 sodium chloride1 kieserite1 carnallite and bischofite4#abi ,the alternate layers of anhydrite and sodium chloride noticeable in some desiccated sea beds is probably the result of alterations in temperature1 anhydrite being less soluble1 and sodium chloride somewhat more soluble in hot than in cold water4 ,during warm weather there would be a greater tendency for anhydrite to separate and in colder weather for sodium chloride to be precipitated4 ,anhydrite at the surface would gradually absorb water vapor from the atmosphere and be transformed to gypsum4#acj #abi ,it will be interesting to compare with the above the following brief description of the ,stassfurt salt deposits1 taken from ,ries's ,economic ,geology of the ,united ,states1 7#aije71 p4 #abg4 8,at the bottom is the main bed of rock salt which is broken up into layers #b-e inches thick by layers of anhydrite4 ,above this come #bjj feet of rock salt1 with which are mixed layers of magnesium chloride and polyhalite4444 ,resting on this is #ahj feet of rock salt1 with alternating layers of sulphates chiefly kieserite1 the sulphate of magnesia4 ,these layers are about #a foot thick4 ,lastly1 and uppermost1 is a #ace-;foot bed consisting of a series of reddish layers of rock salts of magnesia and potassium1 kainite 444 kieserite 444 carnallite 444 tachhydrite 444 as well as masses of snow-white boracite40 #acj ,as examples1 some of the gypsum deposits of ,kansas may be cited1 according to ,haworth1 ,mineral resources of ,kansas1 #ahig1 p4 #fa1 and the classical case at ,bex1 ,switzerland1 described by ,j4 ,g4 ,f4 ,charpentier1 ,uber die ,salz-,lagersttte von ,bex3 ,ann4 ,phys4 ,chim41 #c1 #ge-hj1 7#ahbe71 and by ,g4 ,bischof1 ,elements of chemical and physical geology1 ,london1 #ahed-eh1 ,vol4 ,i1 p4 #cej-a4 ,besides the principal salts just described1 there may separate at one concentration or another other various double salts including langbeinite 7#b,mg,s,o4,k,,so71 polyhalite 7,k,,so4,mg,s,o4#b;,ca,s,o4#b;,h,o71 glauberite 7,ca,s,o4,na,,so71 syngenite 7,ca,s,o4,k,,so4,h,o71 potassium pentasulphate 7,k,,so4#e;,ca,s,o4,h,o71 krugite 7#d;,ca,s,o4,k,,so4,mg,s,o4#b;,h,o71 and possibly others4 ,these are all stable over very restricted ranges of concentration1 however1 and if formed1 probably seldom persist1 but pass over to more stable salts as the desiccation proceeds1 and have little more than a passing theoretical interest4 ,the addition of carbonates to the system introduces some further modifications4#aca ,in this case lime carbonate is the first salt to be precipitated1 followed probably by the same order of deposition as outlined above4 ,as the mother liquor becomes more concentrated1 it apparently loses its alkaline character1 for the addition of an alcoholic solution of phenolphthalein does not produce the characteristic red color4 ,that the solution does actually contain dissolved carbonates is shown by the appearance of the red color on diluting a portion of the mother liquor with distilled water4 ,an interesting example in nature is furnished by the ,great ,salt ,lake1 ,utah4 ,a test of the water of this lake in #ahii gave no alkaline reaction with phenolphthalein1 but the reaction appeared promptly when distilled water was added1 and further examination showed the water to contain about #j4jab per cent4 sodium carbonate4#acb ,slosson has reported similar cases in ,wyoming4#acc #aca ,the action of water and aqueous solutions upon soil carbonates1 by ,frank ,k4 ,cameron and ,james ,m4 ,bell1 ,bull4 ,no4 #di1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture1 #aijg4 #acb ,application of the theory of solutions to study of soils1 by ,f4 ,k4 ,cameron1 ,report ,no4 #fd1 ,field ,operations of the ,bureau of ,soils1 #ahii1 p4 #adi4 #acc ,alkali lakes and deposits1 by ,w4 ,c4 ,knight and ,e4 ,e4 ,slosson1 ,bull4 ,no4 #di1 ,wyoming ,agr4 ,expt4 ,station1 #aija1 p4 #ajh4 ,one 8black alkali0 system has been studied with some approach towards completeness4#acd ,in this case magnesium and potassium salts are not present1 the system being composed of water1 carbon dioxide1 chlorides1 sulphates1 sodium and calcium salts1 with the condition imposed1 that the bases are present in amounts more than equivalent to the sulphuric and hydrochloric acids4 ,on desiccation at #be ,c calcium carbonate first appears followed by gypsum and then sodium sulphate decahydrate4 ,next appears a double salt 7#b;,ca,s,o4#c,na,,so7 followed by anhydrous sodium sulphate1 the ,glauber's salt which formerly crystallized being no longer stable4 ,sodium chloride then precipitates and the concentration finally reaches a point where gypsum is no longer stable1 and the final group of salts in contact with the evaporating solution under conditions of stable equilibrium consists of calcium carbonate1 the double sulphate of soda and lime1 anhydrous sodium sulphate and sodium chloride4 #acd ,the solubility of certain salts present in alkali soils1 by ,frank ,k4 ,cameron1 ,j4 ,m4 ,bell and ,w4 ,o4 ,robinson1 ,jour4 ,phys4 ,chem41 #aa1 #cif-dbj1 7#aijg74 ,the desiccation of a lake which serves as the final repository of a regional drainage involves essentially the principles just discussed4#ace ,the constituents involved are the same4 ,a serious problem involved in the consideration of this source of 8alkali0 is the high ratio of chlorine to the other constituents1 in view of its very low ratio in the rocks from which it comes4 ,the explanation undoubtedly involves the fact that the carbonates and sulphates are constantly being removed as calcium salts from a body of water which is more or less continuously receiving the drainage of any considerable watershed1 and is at the same time subject to a relatively high rate of evaporation4 ,the chlorine forming only very soluble salts under such conditions would be segregated and concentrated in the residual mother liquor4 ,most difficult is it to account for the relatively high ratio of sodium to potassium in alkali from such an origin4 ,some light is thrown on the subject by the progressive changes in concentration of a lake water which receives a regional drainage under arid conditions4 ,to this end are given the following results of analyses of the waters of ,utah ,lake1 made at different times#acf over an interval of twenty years1 and showing that there is a segregation of chlorine and sodium taking place1 although in this case the lake has an outlet in the ,jordan ,river4 #ace ,it has been suggested that the fact that shales or similar geological deposits are frequently to be found near alkali areas1 indicates that the shales are the principal sources of the alkali4 ,it is supposed that the constituents of the alkali salts were formed by the action of water on the shale minerals at or about the time the shales were deposited1 and carried down with the latter4 ,subsequently the alkali has been leached out to appear at the surface of soils1 generally at a lower level than are the shales4 #acf ,the water of ,utah ,lake1 by ,f4 ,k4 ,cameron3 ,jour4 ,am4 ,chem4 ,soc41 #bg1 #aac-aaf1 7#aije74 ,,analyses ,,of ,,the ,,water ,,of ,,utah ,,lake4 ,,results ,,in ,,parts ,,per ,,million ,clarke ,cameron ,brown ,seidell ,brown #ahhc #ahii #aijc #aijdacg #aijdach ---------------------------------------- ----------- ,ca #ee4h #fg4f #hj #fg4g #fg ,sr -- -- -- #a4g -- ,mg #ah4f #ac4h #ib #gc4e #hf ---------------------------------------- ----------- ,na #ag4g #bcc4g #bdg #bjg4b #bcj ,k 8 8 #cj #be4h #bb ---------------------------------------- ----------- ,li -- -- -- #j4g -- ,,so #acj4f #bcf4g #cfe #ccb4i #cgh ,cl #ab4d #caf4e #ccf #bhh4e #ccg ,,hco -- -- #bff #bje4e #aid ,,co #fj4i #bc4g -- #bd4j #aa ,si,o #aj4j -- -- #bb4f #bh ---------- ---------- ---------- ---------- ---------- ,total #cjf4j #hib4j #adaf #abej4a #acec ---------------------------------------- ----------- #acg ,sample collected ,may #ah4 ,lake unusually high4 #ach ,sample collected ,aug4 #ca4 ,lake still high for that season of the year4 ,the third general origin of alkali supposes that wind-borne sea-spray carries into the air salts which are left in very fine particles on the evaporation of the water1 or are deposited on the ordinary atmospheric dust and carried over the land2 and that this dust is precipitated here and there as may be determined by the various meteorological conditions which it encounters4 ,all the land surface is supposed to be receiving more or less of it from time to time1 but in arid regions the rainfall and drainage is not sufficient to return to the sea as much as is received therefrom4#aci #aci ,for a recent interesting and valuable discussion of this subject with reference to a particular area1 see3 ,the origin of the salt deposits of ,rajputana1 by ,sir ,thomas ,h4 ,holland and ,w4 ,a4 ,k4 ,christie1 ,records of the ,geological ,survey of ,india1 #ch1 #aed-ahf1 7#aiji74 ,it is very probable that wind-borne salts from the sea are being carried over and to some extent being deposited on all the land surfaces of the earth4 ,to what extent this process is taking place1 and whether it is sufficient to account for the alkali of any particular region1 available data fail to answer satisfactorily4 ,probably it is always associated with one of the origins of alkali already discussed and is in itself generally of secondary importance4 ,an argument frequently advanced against the validity of the hypothesis that wind-borne sea-spray is the origin of alkali is that the relative proportions of the several constituents in 8alkali0 are seldom if ever those obtaining in sea water4 ,this argument does not take into consideration1 however1 that the several salts in the spray probably separate into crystals of widely different size and specific gravities1 and there may well be taking place a selective or sorting action by the wind4 ,more important1 undoubtedly1 is the selective action taking place in the soil itself2 it can only be an accidental coincidence that the constituents of alkali in any particular occurrence should have the same quantitative relations as in the material from which it originated1 no matter what may have been the nature of its origin4 ,in the field1 alkali is found in a bewildering array of forms and types4 ,quite different combinations of constituents may be found in the same field within a few rods or even a few feet1 and each case appears to have a distinct origin1 to be in fact a law unto itself4 ,each alkali deposit represents generally the resultant from a mixture of salt which has been dissolved and reprecipitated a number of times1 and which while dissolved has been seeping through the soil under gravitational forces1 or has been moving through the soil as film water under capillary stresses4 ,in either event the salt mixture has been subject to the power for selective absorption peculiar to the particular soil mass through which it has been moving4 ,re-solution is seldom an instantaneous process1 and different rates of solution necessarily involve some separation of salts4 ,finally the alkali deposit is usually so mixed with other soil material that there cannot be recognized the characteristic solid phases 7such1 for instance1 as the double sulphates of calcium and another base7 which serve as guides in laboratory studies and in certain salt mines4 ,even if the characteristic salts are deposited in surface soils1 it is very doubtful1 owing to their hygroscopicity1 if any but gypsum1 halite and ,glauber's salt can persist for any length of time4 ,the alternations of temperature from night to day characteristic of arid regions1 with precipitation of dews1 might easily be expected to make noticeable and rapid changes in the characteristics of any given alkali or salt mixture4 ,it is not surprising1 therefore1 that attempts to account for the genesis and present appearance of an alkali deposit by comparison with artificial depositions of salt mixtures1 as worked out in the laboratory1 have generally been disappointing4 ,on the other hand1 laboratory studies have been quite fruitful in elucidating the phenomena taking place on the leaching of alkali from a soil1 or so-called 8alkali reclamation40 ,whatever the origin of the alkali1 its segregation at or near the surface of the soil is everywhere much the same2 that is1 there is a translocation and segregation of soluble salts in the below-surface seepage waters1 determined mainly by the topographic features1 but partly by the texture and structural properties of the soil and subsoil1 with a subsequent rise as capillary water consequent upon evaporation at the surface4 ,precipitation of the solutes may take place at the surface2 more commonly it takes place a few inches below1 owing to the fact that under conditions of rapid evaporation1 there is ordinarily a discontinuance in the capillary columns or the film water at a point below the surface of the soil1 the water diffusing thence into the above-surface atmosphere as the vapor phase4 ,the composition of alkali is varied4 ,in the vast majority of cases1 the world over1 the predominating compound is sodium chloride4 ,when calcium carbonate is a conspicuous component of the soil1 as a hard-pan or otherwise1 sodium carbonate or black alkali is also generally present1 or apt to appear when the land is irrigated4 ,when calcium sulphate or gypsum is likewise present1 there is less probability of appreciable amounts of black alkali1 and where gypsum predominates or the calcium carbonate is present in relatively inappreciable amounts1 black alkali is generally absent1 and sodium sulphate is an important constituent of the alkali4 ,relative rates of diffusion1 selective absorption1 and sometimes other factors are prominent1 however1 and the character of the alkali in different spots within a few yards of one another may differ greatly4 ,one of the most interesting manifestations of alkali is the occasional occurrence of a predominating amount of calcium chloride which1 as a result of its unusually high hygroscopicity1 renders the soil damper1 and therefore darker in color than the surrounding soil1 and frequently causes even experts to suspect the presence of black alkali4 ,its true nature can1 of course1 be determined by a simple chemical examination4 ,the effect of alkali on the physical properties of the soil is often very marked1 aside from the cementing action or hard-pan formation by the carbonate or sulphate of lime4 ,black alkali1 by dissolving and segregating the organic matter at the surface1 removes from the lower soil layers the 8humus0 compounds which are of enormous importance to the maintenance of a soil structure favorable to plant growth4 ,moreover1 black alkali is one of the best of deflocculating agents1 and consequently soils where it is a noticeable component1 frequently puddle with great readiness and are reclaimed with the utmost difficulty4 ,most of the other constituents of alkali1 however1 are flocculating or 8crumbing0 agencies1 and if not present in too large amounts tend to increase the readiness with which the soil can be brought into good tilth4 ,in this latter case1 by separating in the solid phase1 or in forming a viscous soil solution1 near the saturation point1 they sometimes produce a condition in the soil simulating puddling1 and where it occurs below the surface1 called an alkali hard-pan4 ,the management of soils infested with alkali is possible in accordance with a few well established principles4 ,substantial progress has been made in selecting and breeding plants and strains of plants adapted to such soils4 ,extreme cases are the use of the so-called ,australian salt-bushes as forage crops1 and the growing of date-palms which through generations of breeding in the oases of the ,sahara can thrive in lands so salty as to destroy most of the halophilous plants4 ,more interesting is the unwitting development of the farmers of ,utah of strains of wheat and alfalfa which easily withstand three or four times as high a salt content in the soil as do corresponding crops in other alkali regions1 such as ,new ,mexico and ,arizona4#adj ,black alkali1 or one in which sodium carbonate is a prominent constituent1 is especially destructive to vegetation1 not alone on account of a toxic action on plants1 but because in any considerable concentration it has a corrosive action on the plant tissue4 ,not only on this account but also because of its unfortunate effects on the physical properties of the soil1 black alkali has received unusual attention from soil investigators4 ,hilgard#ada has repeatedly urged the use of gypsum as an 8antidote0 to black alkali1 assuming that under conditions of good drainage and aeration a reaction takes place in accordance with the following equation1 ,na,,co ,ca,s,o ,ca,c,o ,na,,so4 #adj ,some mutual relations between alkali soils and vegetation1 by ,thomas ,h4 ,kearney and ,frank ,k4 ,cameron1 ,report ,no4 #ga1 ,u4 ,s4 ,dept4 ,agriculture1 #aijb2 ,the date-palm and its utilization in the ,southwestern states1 by ,walter ,t4 ,swingle1 ,bull4 #ec1 ,bureau of ,plant ,industry1 ,u4 ,s4 ,dept4 ,agriculture1 #aijd2 ,the comparative tolerance of various plants for the salts common in alkali soils1 by ,t4 ,h4 ,kearney and ,l4 ,l4 ,harter1 ,bull4 #aac1 ,bureau of ,plant ,industry1 ,u4 ,s4 ,dept4 ,agriculture1 #aijg2 ,tolerance of alkali by various cultures1 by ,r4 ,h4 ,loughridge1 ,bull4 #acc1 ,california ,agr4 ,expt4 ,sta41 #aija4 #ada ,soils1 by ,e4 ,w4 ,hilgard4 #aijf1 p4 #deg-deh4 ,furthermore1 it has been shown that calcium salts and especially calcium sulphate exercise a marked ameliorating effect on the action of other salts upon growing vegetation4#adb ,on the other hand1 the reaction indicated by the equation just given does not run to an end with complete precipitation of the carbonate1 and the total amount of alkali is increased in the soil by the addition of the gypsum4 ,unfortunately1 ,hilgard's suggestion has not yet acquired the sanction of satisfactory field demonstration1 although it would seem to merit more consideration than has been given it4 ,inasmuch as lime is generally a prominent constituent of soils containing black alkali1 it is possible that the maintenance of good drainage and aeration in the soil is itself the best corrective of black alkali4 #adb ,with the salts occurring in alkali1 it is a generality that the effects produced on higher green plants are relatively less with mixtures than with an equivalent amount of a single salt4 ,it has recently been shown1 however1 that the contrary is true for at least some kinds of bacterial flora4 ,see1 ,on the lack of antagonism between certain salts1 by ,c4 ,b4 ,lipman1 ,bot4 ,gaz41 #di1 #da-ej1 7#aiaj74 ,the best use of alkali soils involves irrigation1 and it is in the application of irrigation waters that management of alkali soils finds its most highly developed and most important expression4 ,with light sandy soils it has sometimes been found practicable to add sufficient water to carry the alkali down into the soil to such a depth that the crop is well advanced toward maturity before the alkali again rises in sufficient amounts to prove seriously detrimental to the more advanced crops which are generally far more 8alkali resistant0 than the young seedlings or the germinating seeds4 ,in some cases this procedure can be practiced for a number of years without greatly increasing the seriousness of the alkali conditions1 and it may be justified1 for a time at least1 by economic considerations4 ,ultimately1 however1 and more quickly with heavy than with light soils1 increasing amounts of alkali must be brought into the surface soil1 and this method of irrigating should not be considered as anything more than a temporary expedient4 ,the only procedure which should be seriously considered as a permanent system on an alkali soil1 no matter what the texture1 is the installation of underground drains1 for which purpose1 so far1 cylindrical tile drains commend themselves as giving the best results4 ,with a well established system of tile drains1 the alkali and all excess of soluble salts can be removed from the soil above the drains2 and alkali rising from the soil below can1 at least very largely1 be prevented from rising to the upper soil layers4 ,the reclamation of an alkali tract by underdrainage is not1 however1 a necessarily quick operation4 ,generally it must be a matter of several years persistent and careful effort1 but once attained should readily be maintained4 ,the reclamation of an alkali tract by flooding and underdrainage involves the reverse process to the crystallization of salt from a brine4 ,if the water in percolating through the soil were long enough in contact with the salts present to become a saturated solution in equilibrium with them1 then the composition of the resulting solution or drainage water would depend upon the particular solid phases or salts which are present in the soil1 but not on the amounts of these salts2 and the relative proportions of the mineral constituents in the drainage water should remain constant until some one of the solid phases in the soil permanently disappears4 ,in practice1 however1 the water passes through the soil at different rates from time to time1 the flow from the tiles being copious after a flooding but gradually diminishing as time goes on4 ,one or both of two processes can therefore take place4 ,the water may dissolve some of the salts without at any time or place becoming saturated4 ,as the different salts have different rates of solution as well as different absolute solubilities1 it would be expected that not only the concentration of the drainage water1 but the composition of the dissolved salts would change from time to time4 ,on the other hand1 a part of the water may be imagined to percolate slowly through the finer openings1 thus forming a saturated solution with respect to the alkali salts which solution1 however1 will be diluted on entrance to the drains by a part of the water going through the larger soil openings and dissolving but little salt in its passage4 ,in this case1 it would be anticipated that the concentration of the drainage water would increase as the amount of flow diminished but the composition of the dissolved salts would remain practically constant until some one or more of the alkali salts was completely removed4 ,there are1 unfortunately1 but few experimental data by which these can be tested4 ,in the accompanying table are given the results of an investigation on the reclamation of an alkali tract near ,salt ,lake ,city1 ,utah1 where observations on the composition of the drainage water were made at frequent intervals for more than three years4#adc #adc ,see1 ,calcium sulphate in aqueous solution1 by ,frank ,k4 ,cameron and ,james ,m4 ,bell1 ,bull4 ,no4 #cc1 #aijf1 p4 #aj and #gj1 and ,reclamation of alkali land in ,salt ,lake ,valley1 ,utah1 by ,clarence ,w4 ,dorsey1 ,bull4 ,no4 #dc1 #aijg1 p4 #ac1 ,bureau of ,soils1 ,u4 ,s4 ,dept4 ,agriculture4 ,at first sight these results might appear to show that the composition of the salts was remaining reasonably constant4 ,this conclusion must be received with caution1 however4 ,variations do occur in the constituents which are present in smaller amount1 but the variations are not systematic and may plausibly be explained by dilution of saturated solution by unsaturated solution on entering the drains4 ,confining attention therefore to the constituents occurring in larger proportions1 namely1 sodium chloride1 sodium sulphate and sodium bicarbonate 7including the normal carbonate7 it should be remembered that the percentage of sodium in these three salts does not vary much1 and the 8constancy0 may be more apparent than real4 ,indeed a close inspection of the results indicates that while the sodium is remaining practically unchanged1 there is some decrease in the chlorine and a corresponding increase in the sulph-ion4 ,from this it would follow that the sodium chloride was being washed out of the soil more rapidly1 proportionately1 than sodium sulphate2 and it would also appear that the solution entering the drains was not in final equilibrium with the salts in the soil4 ,,composition ,,of ,,the ,,salts ,,in ,,the ,,drainage ,,water ,,from ,,the ,,swan ,,tract1 ,,utah ,date ,ca ,mg ,na ,k per cent4per cent4per cent4per cent4 ---------------------------------------- ------------- #aijb--,september #j4ch #j4ej #cc4gd #b4jd ,october #j4bc #j4gh #cd4gc #a4di ,november #j4ai #j4gd #cd4db #a4dj #aijc--,may #j4ch #j4fa #cd4dh #j4hd ,june #j4de #j4he #cd4ah #a4ji ,july #j4ej #j4hj #cd4jf #a4be ,august #j4ce #j4ij #cd4dj #a4ab ,september #j4di #j4gb #cd4ed #a4bd ,october #j4dg #a4jb #cc4dc #a4eb #aijd--;,january #j4ae #j4ge #cc4ic #a4bf ,february #j4cd #j4gh #cd4ei #j4gj ,march #j4bi #j4gg #cd4eg #a4bh ,april #j4bi #j4gj #cd4bh #a4cg ,may #j4ga #j4gd #bf4ib #d4ja ,june #j4cg #j4gj #cb4fj #c4ee ,august #j4cg #j4hf #cc4he #b4ac ,september #j4db #j4gi #cd4aj #a4ce ,october #a4jd #j4fj #cc4ja #a4hf ,december #a4be #j4gj #cb4fb #a4fi #aije--;,february #j4cb #j4fg #cc4ei #j4ii ,march #j4ca #j4ff #cc4df #a4cj ,april #j4ce #j4fe #cd4bj #a4ja ,may #j4de #j4hf #cc4dc #a4bj ,june #j4dj #j4id #cd4je #a4cb ,july #j4cb #j4fi #cc4fg #a4cj ,august #j4ce #a4jd #cc4ab #a4eh ,september #j4db #j4hb #cc4ci #a4bf #aijf--;,january #j4ee #j4hd #cc4ab #a4aa ,,so ,cl ,,hco ,,co ,date per cent4per cent4per cent4per cent4 ---------------------------------------- ------------- #aijb--,september #ah4fb #cg4gf #f4di #j4dh ,october #ai4ad #ci4eb #e4jf #j4bi ,november #ah4fa #dj4df #c4ie #j4bc #aijc--,may #bi4ij #ch4ai #d4cj #j4be ,june #ag4eb #da4jj #d4bc #j4db ,july #ah4bd #dj4bd #d4fg #j4cj ,august #ag4ae #db4cg #c4dh #j4af ,september #ag4ca #db4jb #c4cf #j4cc ,october #af4jh #dc4bh #c4cc #j4cj #aijd--;,january #bj4jh #cf4fd #f4id #j4be ,february #ah4ie #dj4ae #d4di ---- ,march #af4ca #db4bh #c4ha #j4ai ,april #bj4ic #ch4jd #c4cc #a4jf ,may #ba4bf #dj4ic #d4je #a4ch ,june #ai4id #cg4db #d4je #a4cg ,august #ag4ab #da4ca #c4bj #a4af ,september #ai4ja #ci4he #d4aa #j4cg ,october #ba4db #cf4fc #d4fh #j4gf ,december #ai4hi #cg4dd #f4ah #j4bb #aije--;,february #bb4cj #cc4cb #h4de #j4cf ,march #ba4fj #cc4hf #h4df #j4ce ,april #bj4jc #cf4ii #f4bb #j4ee ,may #bj4ei #cf4jd #f4if #j4dg ,june #bj4hi #ce4he #e4ga #j4hd ,july #ba4ag #cd4id #g4bc #j4fh ,august #ba4eh #ce4ib #e4gb #j4ii ,september #ba4ah #cd4he #g4da #j4fg #aijf--;,january #ba4aj #cd4ce #h4eg #j4cf ---------------------------------------- ------------- ,how long drainage must continue before there is a radical change in the composition of the seepage water cannot be predicted1 and unfortunately data regarding this point are not available4 ,it is certain that in time some one or more of the salts in the soil would be removed and the nature of the drainage water would be changed4 ,alterations in the composition of the drainage water furnish the readiest as well as the best guides as to the changes and the nature of the changes taking place in the soil during the process of reclamation4 ,as a practical matter it should be borne in mind that the persistence of the several salts of the alkali mixture does not mean necessarily that they are evenly distributed in the soil2 while yet determining the composition of the water entering the drain1 they may have disappeared from the upper soil layers which then may hold a solution of quite different character1 suited to the support of crops4 ,in the case just cited the soil contained1 before drainage operations were commenced1 upwards of #b4g per cent4 of readily soluble salts and would not support any growth other than salt-bushes and similar halophilous plants4 ,four years later the soil contained less than #j4c per cent4 soluble salts and yielded a very satisfactory crop of alfalfa4 ,in such cases1 however1 the land cannot be considered as finally reclaimed until a material change in the composition of the drainage water shows that there has been a complete removal of some of the solid salts from that portion of the soil feeding the drains4 ,the rate at which alkali can be leached from a soil is dependent in a large measure upon the absorptive properties of the soil1 and to some extent upon the nature of the salts composing the alkali4 ,the leaching is more rapid from sandy than from clay soils1 and white alkali is leached more readily than is black4 ,in general1 however1 the same laws hold here as in any leaching of a solute from an absorbent1 and it has been shown that even in the case of black alkali1 the rate of removal under a constant leaching follows the law dx ---------- ,k 7,a - x74#add dt #add ,the removal of 8black alkali0 by leaching1 by ,f4 ,k4 ,cameron and ,h4 ,e4 ,patten1 ,jour4 ,am4 ,chem4 ,soc41 #bh1 #afci1 7#aijf74 ,in practice1 the water does not percolate through the soil under a constant 8head10 but the flow is intermittent1 so that the value of the above formula is mainly academic4 ,on the other hand1 if the drainage between floodings is thorough1 this procedure should be more efficient than any other for causing a rapid removal of the alkali salts1 if1 as is generally the case1 a limited quantity of water is available4 ,finally1 it remains to be pointed out that the use of excessive amounts of water on alkali tracts is quite as unfortunate in its effects as the use of too little4 ,if water be added to an undrained soil or in excess of the capacity of the drains to remove it1 incalculable harm may be done by enormously increasing in the surface soil the amount of salts brought up from the lower layers as the capillary stream rises to the surface in consequence of evaporation there4 ,should the wetting of the soil proceed so far as to establish good capillary connection with the permanent ground water1 the harm may be sufficient to offset in a few weeks or months expensive reclamation efforts of years4 ,the harm to the tract where the water is added may be far less than the harm done to other areas4 ,a large proportion of existing alkali deposits or 8spots0 results from the evaporation of seepage waters coming sometimes from considerable distances4 ,the over-wetting of a soil means the production of seepage waters which are to appear at the surface somewhere else1 generally at a lower level1 and frequently means the more or less complete ruin of the soils of the lower level4 ,the experience of ,india1 ,africa and our own arid states in the increase of alkali spots following the introduction of irrigation1 added to our present theoretical knowledge1 should make the planning of an irrigation project without adequate drainage provisions1 a stupidity1 and its accomplishment a public crime4 ,quite as important is the development of a public opinion that the individual cultivator who deliberately or carelessly uses excessive amounts of water on his tract is a serious enemy to the body politic1 and should be treated as such4 ,,index4 ,absorbents1 ,influence on soil extracts1 #ch ,absorption by soils1 #i1 #ei1 #fe formula1 #fb of dyes1 #fj1 #fa rate1 #fc selective1 #fa ,acid digestion of soils1 #aa1 #ab ,adsorption1 #i1 #fj ,alkali1 #aaj1 #aah ,effect on soils1 #aah ,order of deposition1 #aab ,reclamation1 #aag1 #aba ,source1 #aaa1 #aag ,antagonism between salts1 #abj ,apophyllite1 ,crystallization from water1 #ce ,apple trees1 ,effect of grass on1 #ih ,appleyard1 ,james ,r4 ,see ,walker1 ,james1 and ,appleyard1 ,james ,r4 ,ash analyses1 #aa1 #ac ,association of ,official ,agricultural ,chemists' analyses1 quoted1 #ab cited1 #ab 8official method01 #aj1 #ab 8,available0 and 8non-available0 plant-food elements1 #h ,averitt1 ,s4 ,d4 ,see ,peter1 ,alfred ,m41 and ,averitt1 ,s4 ,d4 ,bacteria in soils1 #ajc ,bailey1 ,liberty ,h41 cited1 #e ,balance between supply and removal of mineral plant nutrients1 #ge ,barium in soils1 #ajg ,bardt1 ,a4 ,see ,doroshevskii1 ,a4 and ,bardt1 ,a4 ,becquerel1 ,antoine ,c41 cited1 #fg quoted1 #fh ,bell1 ,james ,m41 and ,cameron1 ,frank ,k41 cited1 #bh ,bell1 ,james ,m4 ,see also ,cameron1 ,frank ,k41 and ,bell1 ,j4 ,m42 ,cameron1 ,frank ,k41 ,bell1 ,j4 ,m41 and ,robinson1 ,w4 ,o4 ,benedick1 ,carl1 cited1 #ee ,birner1 ,h41 and ,lucanus1 ,b41 cited1 #gj ,bischof1 ,gustav1 cited1 #aac ,black alkali1 #aaj1 #aad1 #aai1 #abd ,blanck1 ,edward1 cited1 #fc ,breazeale1 ,james ,f41 acknowledgments1 #hj cited1 #ga ,see also ,cameron1 ,frank ,k41 and ,breazeale1 ,j4 ,f42 ,le,clerc1 ,j4 ,a4 and ,breazeale1 ,j4 ,f4 ,briggs1 ,lyman ,j41 cited1 #ee and ,lapham1 ,macy ,h41 cited1 #da and ,mc,lane1 ,john ,w41 cited1 #bf ,martin1 ,f4 ,o41 and ,pearce1 ,j4 ,r41 cited1 #ca ,brooks1 ,william ,p41 cited1 #e ,brown1 ,bailey ,e41 cited1 #df quoted1 #df1 #aae ,bryan1 ,h4 ,see ,davis1 ,r4 ,o4 ,e41 and ,bryan1 ,h4 ,buckingham1 ,edgar1 cited1 #cj ,burney1 ,w4 ,b41 quoted1 #ih ,cameron1 ,frank ,k41 cited1 #aaj1 #aad1 #aae ,see also ,bell1 ,james ,m41 and ,cameron1 ,frank ,k42 ,kearney1 ,thomas ,h4 and ,cameron1 ,frank ,k42 ,whitney1 ,milton1 and ,cameron1 ,frank ,k4 and ,bell1 ,james ,m41 cited1 #ca1 #ch1 #ej1 #aac1 #abb and ,breazeale1 ,james ,f41 cited1 #fb and ,gallagher1 ,francis ,e41 cited1 #bd and ,patten1 ,harrison ,e41 cited1 #fc1 #abd and ,robinson1 ,william ,o41 cited1 #bg1 #ec ,bell1 ,james ,m41 and ,robinson1 ,william ,o41 cited1 #aad ,calcium nitrate1 basic1 #ajh ,carbon dioxide in the soil1 #ec ,charpentier1 ,jean ,g4 ,f41 cited1 #aac ,chemical analysis of soils4 ,see ,soil analysis--,chemical4 ,chesneau1 ,g41 cited1 #fh ,christie1 ,w4 ,a4 ,k4 ,see ,holland1 ,sir ,thomas ,h41 and ,christie1 ,w4 ,a4 ,k4 ,clarke1 ,frank ,wigglesworth1 cited1 #gf1 #aae ,coffey1 ,george ,n41 quoted1 #bc ,concentration of mineral constituents1 #ci ,concentration1 ,plant growth and1 #gj ,cracking of soil1 #bb ,creep1 #ai ,creighton1 ,henry ,j4 ,m4 ,see ,findlay1 ,alexander1 and ,creighton1 ,henry ,j4 ,m4 ,critical moisture content1 #bd ,crop control methods1 #g1 #aje plants defined1 #a producing power and aqueous extract1 #ha rotation1 ,natural1 #ig ,objects of1 #d yields increasing1 #af ,crumb structure of soils1 #be ,crumbing1 #bg1 #aai ,cushman1 ,allerton ,s41 cited1 #cf 8,cut-off01 #bb1 #ge ,cyanamid1 #ajh ,czapek1 ,friedrich1 ,experiments on root etchings1 #i ,criticism of ,molisch1 #aja ,dachnowski1 ,alfred1 cited1 #hh ,darbishire1 ,francis ,v41 and ,russell1 ,edward ,j41 cited1 #ajc ,darwin1 ,horace1 cited1 #bb ,davis1 ,r4 ,o4 ,e41 quoted1 #fc and ,bryan1 ,h41 cited1 #ee ,de ,candolle1 ,augustin ,p41 cited1 #ig ,degradation of rocks1 #a ,de ,roode1 ,rudolph ,j4 ,j41 quoted1 #ih ,diaspore1 #cd ,dittrich1 ,max41 cited1 #ac ,doroshevskii1 ,a41 and ,bardt1 ,a41 cited1 #ce ,dorsey1 ,clarence ,w41 cited1 #aaj1 #abb ,drainage waters1 ,composition1 #abd ,drought limits defined1 #bi ,dunnington1 ,francis ,p41 cited1 #ih ,dust1 #bj ,dyer1 ,bernard1 cited1 #dj method of soil analysis1 #aj quoted1 #f ,dynamic nature of soil phenomena1 #ah ,earthworms1 #bb ,european soils1 analyses1 #af ,erosion1 #bj ,etchings1 ,root1 #i ,ewart1 ,a4 ,j41 cited1 #ah1 #gb1 #gc ,excreta1 ,toxic1 #ii1 #ajj1 #ajc 8,factors01 #aa ,failyer1 ,george ,h41 cited1 #ajg ,see also ,schreiner1 ,oswald1 and ,failyer1 ,george ,h4 ,smith1 ,joseph ,g41 and ,wade1 ,h4 ,r41 cited1 #cb ,fairy rings1 #ih ,feldspars1 #ce1 #ch1 #ee ,fertilizers1 #d1 #hc1 #aje ,film water1 #bd tenacity1 ,experiments1 #be ,findlay1 ,alexander1 and ,creighton1 ,henry ,j4 ,m41 cited1 #ec ,fine a soil1 to1 #d ,fischer1 ,emil1 and ,schmidmer1 ,edward1 cited1 #fa 8,fly-off01 #bb1 #ge ,frear1 ,william1 cited1 #e ,free1 ,edward ,elway1 cited1 #bj ,friedel1 ,charles and ,sarasin1 ,edmond1 cited1 #cd ,gallagher1 ,francis ,edward4 ,see ,cameron1 ,frank ,k4 and ,gallagher1 ,francis ,e4 ,gannett1 ,henry1 cited1 #gf ,gaudechon1 ,h4 ,see ,muntz1 ,a41 and ,gaudechon1 ,h4 ,geikie1 ,sir ,archibald1 cited1 #ge ,gels1 #cf ,gilbert1 ,joseph ,h41 cited1 #ih ,gonnard1 ,f41 cited1 #ce 8,good0 and 8poor0 soils compared1 #hj ,graham1 ,thomas1 cited1 #fg ,granulate a soil1 to1 #d ,grass1 ,effect on apple trees1 #ih ,gravitational water1 #bc ,great ,salt ,lake1 ,reaction of water1 #aac ,green manure1 ,effect on soil extracts1 #hg ,gypsum on alkali soils1 #aai ,hardpan1 #aaa ,harter1 ,leonard ,l4 ,see ,kearney1 ,thomas ,h41 and ,harter1 ,l4 ,l4 ,hartwell1 ,burt ,l41 ,wheeler1 ,h4 ,j41 and ,pember1 ,f4 ,r41 cited1 #gd ,haselhoff1 ,emil4 ,see ,knig1 ,joseph1 and ,haselhoff1 ,e4 ,haworth1 ,erasmus1 cited1 #aac ,heileman1 ,william ,h41 quoted1 #fe ,heterogeneity of soils1 #a1 #ba1 #cb1 #gi ,hilgard1 ,eugene ,w41 cited1 #e1 #f1 #ch1 #dj1 #aai ,method of soil analysis1 #aj ,hillebrand1 ,william ,f41 cited1 #ac ,hills1 ,joseph ,l41 cited1 #e ,holland1 ,sir ,thomas ,h41 and ,christie1 ,w4 ,a4 ,k41 cited1 #aaf ,hulett1 ,george ,a41 cited1 #fh ,humic acids1 #ee ,humus1 #fa ,hutchinson1 ,henry ,b4 ,see ,russell1 ,edward ,j41 and ,hutchinson1 ,henry ,b4 ,hydrolysis1 #cc ,imbibition1 #ei ,irrigation1 #abj ,johnson1 ,samuel ,w41 cited1 #dj1 #gg quoted1 #b ,kahlenberg1 ,louis1 and ,lincoln1 ,azariah ,t41 cited1 #ce ,kaolinite1 #cd ,kearney1 ,thomas ,h41 and ,cameron1 ,frank ,k41 cited1 #aai and ,harter1 ,leonard ,l41 cited1 #aai ,kentucky agricultural experiment station1 ,method of soil analysis1 #aj ,king1 ,franklin ,h41 cited1 #ge1 #gf1 #gg quoted1 #df1 #gf ,knight1 ,wilbur ,c41 and ,slosson1 ,edwin ,e41 cited1 #aad ,knig1 ,joseph1 and ,haselhoff1 ,e41 cited1 #h ,kossovich1 ,petr4 ,s41 ,experiments on root etchings1 #i ,lagergren1 ,sten1 cited1 #bf ,lake desiccation1 #aad ,lapham1 ,macy ,h4 ,see ,briggs1 ,lyman ,j41 and ,lapham1 ,macy ,h4 ,lawes1 ,john ,b41 and ,gilbert1 ,joseph ,h4 ,see ,gilbert1 ,joseph ,h4 ,leather1 ,j4 ,walter1 cited1 #bc ,le ,clerc1 ,j4 ,arthur1 and ,breazeale1 ,james ,f41 cited1 #ad ,lemberg1 ,johann ,t41 cited1 #ce ,liebig1 ,justus1 cited1 #h1 #ig ,liebrich1 ,a41 cited1 #cd ,liebreich1 quoted1 #fh ,lieving1 quoted1 #fh ,lincoln1 ,azariah ,t4 ,see ,kahlenberg1 ,louis1 and ,lincoln1 ,azariah ,t4 ,lipman1 ,jacob ,g41 cited1 #gb1 #ajc ,see also ,voorhees1 ,edward ,b41 and ,lipman1 ,jacob ,g4 ,lipman1 ,c4 ,b41 cited1 #abj ,litmus1 ,absorption of1 #ff as indicator1 #ff ,livingston1 ,burton ,e41 cited1 #he1 #hh1 #ig ,loughridge1 ,robert ,h41 cited1 #bh1 #aai ,lucanus1 ,b4 ,see ,birner1 ,h41 and ,lucanus1 ,b4 ,mc,gee1 ,w4 ,j41 quoted1 #bb1 #gf ,mc,lane1 ,john ,w4 ,see ,briggs1 ,lyman ,j41 and ,mc,lane1 ,john ,w4 ,manure1 ,stable1 ,effect on soil extracts1 #hd ,martin1 ,f4 ,oskar4 ,see ,briggs1 ,lyman ,j41 ,martin1 ,f4 ,o41 and ,pearce1 ,j4 ,r4 ,maxwell1 ,walter1 ,method of soil analysis1 #aj ,mechanical analysis1 #ca ,merrill1 ,george ,p41 cited1 #i ,meyerhoffer1 ,wilhelm1 cited1 #aaa ,meyer1 ,victor1 cited1 #fg ,minchin1 ,george ,m41 cited1 #bf ,mineral constituents of soil solution1 #ca1 #cg ,mineral plant nutrients1 balance between supply and removal1 #ge ,mississippi ,river1 ,soil-carrying power1 #ba ,mixing of soils1 #cc ,moisture content1 #bd ,moisture movement into soil1 #bh ,molisch1 ,hans1 cited1 #aja ,mooers1 ,charles ,a41 cited1 #aj ,motion in soils1 #ai ,movement of soils1 #bj ,muntz1 ,a41 and ,gaudechon1 ,h41 cited1 #cj quoted1 #bd ,murray1 ,sir ,john1 cited1 #ge ,newell1 ,frederick ,h41 cited1 #ge ,night-soil1 #ajh ,nitrates in agriculture1 #ajh in soil solution1 #ajc ,nitrogen carriers1 #ajc 8,official method0 of soil analysis1 #aj ,optimum moisture content1 #bd ,organic compounds1 ,effect on plants1 #hb ,organic constituents of soil solution1 #ed1 #gi ,orthoclase1 ,alteration of1 #cc ,ostwald1 ,wo41 cited1 #bh ,oxidizing power of roots1 #aja ,oxygen in the soil1 #ec ,oxystearic acid1 ,toxic to plants1 #if ,patten1 ,harrison ,e41 cited1 #bd1 #be1 #fj ,see ,cameron1 ,frank ,k41 and ,patten1 ,harrison ,e4 and ,waggaman1 ,william ,h41 cited1 #i1 #ei and ,gallagher1 ,f4 ,e41 cited1 #ei ,pearce1 ,julia ,r4 ,see ,briggs1 ,lyman ,j41 ,martin1 ,f4 ,o41 and ,pearce1 ,j4 ,r4 ,pember1 ,f4 ,r4 ,see ,hartwell1 ,burt ,l41 ,wheeler1 ,h4 ,j41 and ,pember1 ,f4 ,r4 ,penfield1 ,samuel ,l41 cited1 #ac ,percolation experiments1 #dg ,peter1 ,alfred1 cited1 #ed and ,averitt1 ,s4 ,d41 cited1 #aj ,pfeffer1 ,wilhelm ,f4 ,p41 cited1 #ah1 #gb1 #gc1 #aja ,phlogiston theory1 #ag ,phosphates1 #ej ,picoline carboxylic acid1 toxic to plants1 #if ,plant-food theory1 #af ,plant growth and concentration1 #gj ,plant nutrients1 ,supply and removal1 #ge ,plot experiments1 #ad 8,poor0 and 8good0 soils compared1 #hj ,pot experiments1 #ad ,puddling1 #be ,pyrogallol1 #hg ,pyrophyllite1 #cd ,ragweed1 #ig1 #ih ,rainfall1 #bb1 #ge ,rajputana1 ,salt deposits1 #aaf ,rayleigh1 ,lord1 cited1 #bf ,reed1 ,howard ,s4 ,see ,schreiner1 ,oswald1 and ,reed1 ,howard ,s42 ,schreiner1 ,oswald1 ,reed1 ,howard ,s41 and ,skinner1 ,j4 ,j4 ,removal of plant nutrients1 ,supply and1 #ge ,reversible reactions1 #cd ,ries1 ,heinrich1 quoted1 #aab ,river waters1 ,concentration of1 #gf ,robinson1 ,william ,o4 ,see ,cameron1 ,frank ,k41 and ,robinson1 ,william ,o42 ,cameron1 ,frank ,k41 ,bell1 ,james ,m41 and ,robinson1 ,w4 ,o4 ,rodewald1 ,h41 cited1 #bd ,rmer1 ,hermann4 ,see ,wilfarth1 ,hermann1 ,rmer1 ,hermann1 and ,wimmer1 ,g4 ,root etchings1 #i ,root growth mechanism1 #ai ,roots of growing plants1 #ah ,rotation of crops1 #ig ,rothmund1 ,v41 cited1 #fh 8,run-off01 #bb1 #ge ,russell1 ,edward ,j41 cited1 #ajc ,see also ,darbishire1 ,francis ,v41 and ,russell1 ,edward ,j4 and ,hutchinson1 ,henry ,b1 cited1 #gb ,sachs1 ,julius1 ,experiments on root etchings1 #i ,salt as fertilizer1 ,common1 #ajh ,sarasin1 ,edmond4 ,see ,friedel1 ,charles1 and ,sarasin1 ,edmond1 #cd ,schmidmer1 ,edward4 ,see1 ,fischer1 ,emil1 and ,schmidmer1 ,edward4 ,schreiner1 ,oswald1 quoted1 #ajb and ,failyer1 ,george ,h41 cited1 #da1 #dg and ,reed1 ,howard ,s41 cited1 #ajj1 #aja and ,shorey1 ,edmund ,c41 cited1 #ie and ,sullivan1 ,m4 ,x41 cited1 #ajj ,reed1 ,howard ,s41 and ,skinner4 ,j4 ,j41 quoted1 #hi ,sea water1 ,desiccation of1 #aaa ,seedlings1 ,growth of1 #gd1 #hj1 #hb1 #hd1 #hf1 #hh1 #ajj1 #ajb ,seedlings1 ,toxic action of acids and salts1 #fb ,seidell1 ,atherton1 quoted1 #aae ,shaler1 ,nathaniel ,s41 cited1 #bj ,shorey1 ,edmund ,c41 cited1 #ie ,see also ,schreiner1 ,oswald1 and ,shorey1 ,e4 ,c4 ,shrinking of soils1 #bb ,skinner1 ,j4 ,j41 quoted1 #ii1 #ajb ,skinner1 ,j4 ,j4 ,see also ,schreiner1 ,oswald1 ,reed1 ,howard ,s41 and ,skinner1 ,j4 ,j4 ,slosson1 ,edwin ,e4 ,see ,knight1 ,wilbur ,c41 and ,slosson1 ,edwin ,e4 ,smith1 ,joseph ,g41 quoted1 #ih ,see also ,failyer1 ,george ,h41 ,smith1 ,joseph ,g41 and ,wade1 ,h4 ,r4 ,sodium chloride as fertilizer1 #ajh ,soil1 the1 #a ,soil amendments1 #aje analysis1 ,chemical1 #h1 #bb ,methods1 #aj atmosphere1 #bc bacteria1 #bc1 #ajc control1 #d methods1 #d erosion1 #bj fatigue1 #ajj heaving1 #bb individuality1 #b management1 #b1 #c1 #d minerals1 ,chief1 #cb moisture defined1 #a not a static system1 #ah phenomena1 ,dynamic nature of1 #ah shrinking1 #bb solution defined1 #a ,analyses1 #ci ,importance of1 #b ,organic constituent of1 #gi ,survey ,field ,book1 cited1 #c translocation by water1 #bj wind1 #ba ,soils1 ,composition of1 #a ,mineral constituents of1 #cb ,moisture content1 #bd ,water extracts of1 #ci ,solid solution defined1 #ei ,solubility of minerals1 #eb1 #ee ,spring1 ,walthre1 cited1 #fg ,structure1 #bg ,subsoils1 ,infertility of1 #hh ,sullivan1 ,michael ,x41 cited1 #ajb quoted1 #fh ,see also ,schreiner1 ,oswald1 and ,sullivan1 ,m4 ,x4 ,supply and removal of plant nutrients1 #ge ,surface effects1 #fg ,surface tension1 #bg ,swan tract1 ,utah1 #abc ,swingle1 ,walter ,t41 cited1 #aai ,taylor1 ,frederick ,w41 cited1 #e ,tennessee agricultural experiment station1 ,methods of soil analysis1 #aj ,thorne1 ,charles ,e41 cited1 #e ,tillage methods1 #d ,objects of1 #d ,tollens1 ,bernhard ,c4 ,g41 cited1 #ad ,toxic excreta of roots1 #ii1 #ajj1 #ajc ,udden1 ,johan ,august1 quoted1 #ba ,u4 ,s4 ,dept4 of ,agriculture1 ,bureau of ,soils4 ,see ,soil ,survey ,field ,book4 ,u4 ,s4 ,geological ,survey1 cited1 #ac ,underdrainage1 #aba ,utah ,lake water analyses1 #aae ,van ,hise1 ,charles ,r41 cited1 #ce1 #cf van't ,hoff1 ,jakob ,h41 cited1 #fg1 #aaa ,voorhees1 ,edward ,b41 and ,lipman1 ,jacob ,g41 cited1 #gb1 #ajc ,wade1 ,harold ,r4 ,see ,failyer1 ,george ,h41 ,smith1 ,joseph ,g41 and ,wade1 ,h4 ,r4 ,waggaman1 ,william ,h4 ,see ,patten1 ,harrison ,e41 and ,waggaman1 ,william ,h4 ,walker1 ,james1 and ,appleyard1 ,james ,r41 cited1 #fj ,washington1 ,henry ,s41 cited1 #ac ,water1 ,movement into soils1 #bh vapor1 ,movement in soils1 #bi ,way1 ,john ,t41 cited1 #i ,weeds1 ,analyses of1 #ih ,weinschenk1 ,e41 cited1 #ce ,wheeler1 ,homer ,j41 cited1 #gd ,wheeler1 ,homer ,j4 ,see also ,hartwell1 ,burt ,l41 ,wheeler1 ,h4 ,j41 and ,pember1 ,f4 ,r4 ,white alkali1 #aaj1 #aaa ,whitney1 ,milton1 cited1 #af and ,cameron1 ,frank ,k41 cited1 #bf1 #db ,wilfarth1 ,hermann1 ,rmer1 ,hermann1 and ,wimmer1 ,g41 cited1 #ad ,willard1 ,julius ,t41 cited1 #e ,wimmer1 ,g4 ,see ,wilfarth1 ,hermann1 ,rmer1 ,hermann1 and ,wimmer1 ,g4 ,wind1 #bj ,carrying power of1 #ba ,wind-borne soil material1 #ba1 #cc ,whler1 ,friedrich1 cited1 #ce ,wolff1 ,emil ,t4 von1 tables1 cited1 #gg ,woburn1 ,experiments at1 #ih ,young1 ,thomas1 cited1 #bf ,zeolites1 #i1 #cd1 #ce ,scientific ,books ,published by ,,the ,,chemical ,,publishing ,,company ,,easton1 ,,pa4 ,,benedict--,elementary ,organic ,analysis4 ,small #hvo4 ,pages ,,vi #hb4 #ae ,illustrations #a4jj ,,bergey--,handbook of ,practical ,hygiene4 ,small #hvo4 ,pages #afd #a4ej ,,biltz--,the ,practical ,methods of ,determining ,molecular ,weights4 7,translated by ,jones74 ,small #hvo4 ,pages ,,viii #bde4 #dd ,illustrations #b4jj ,,bolton--,history of the ,thermometer4 #abmo4 ,pages #if4 #f ,illustrations #a4jj ,,colby--,reinforced ,concrete in ,europe4 #hvo4 ,pages ,x #bfj #c4ej ,,emery--,elementary ,chemistry4 #abmo4 ,pages ,,xiv #fff4 #aia ,illustrations #a4ej ,,engelhardt--,the ,electrolysis of ,water4 #hvo4 ,pages ,x #adj4 #ij ,illustrations #a4be ,,gilman--,a ,laboratory ,outline for ,determinations in ,quantitative ,chemical ,analysis4 ,pages #hh #j4ij ,,guild--,the ,mineralogy of ,arizona4 ,small #abmo4 ,pages #ajd4 ,illustrated #a4jj ,,hantzsch--,elements of ,stereochemistry4 7,translated by ,wolf74 #abmo4 ,pages ,,viii #bjf4 #bf ,figures #a4ej ,,hardy--,infinitesimals and ,limits4 ,small #abmo4 ,paper4 ,pages #bb4 #f ,figures #j4bj ,,hart--,chemistry for ,beginners4 ,small #abmo4 ,vol4 ,i4 ,inorganic4 ,pages ,,viii #bad4 #ee ,illustrations1 #b ,plates #a4jj ,,hart--,chemistry for ,beginners4 ,small #abmo4 ,vol4 ,,ii4 ,pages ,,iv #ih4 #aa ,illustrations #j4ej ,,hart--,chemistry for ,beginners4 ,small #abmo4 ,vol4 ,,iii4 ,experiments4 ,separately4 ,pages #fj #j4be ,,hart--,second ,year ,chemistry4 ,small #abmo4 ,pages #afe4 #ca ,illustrations #a4be ,,hart1 ,r4 ,n4--,welding4 #hvo4 ,pages ,,xvi #ahb4 #ic ,illustrations #b4ej ,,heess--,practical ,methods for the ,iron and ,steel ,works ,chemist4 ,pages #fj #a4jj ,,hinds--,qualitative ,chemical ,analysis4 #hvo4 ,pages ,,viii #bff #b4jj ,,howe--,inorganic ,chemistry for ,schools and ,colleges4 #hvo4 ,pages ,,viii #dbb #c4jj ,,landolt--,the ,optical ,rotating ,power of ,organic ,substances and ,its ,practical ,applications4 #hvo4 ,pages ,,xxi #gea4 #hc ,illustrations #g4ej ,,leavenworth--,inorganic ,qualitative ,chemical ,analysis4 #hvo4 ,pages ,,vi #aec #a4ej ,,le ,,blanc--,the ,production of ,chromium and ,its ,compounds by the ,aid of the ,electric ,current4 #hvo4 ,pages #abb #a4be ,,mason--,notes on ,qualitative ,analysis4 ,small #abmo4 ,pages #ef #j4hj ,,meade--,portland ,cement4 #bnd ,edition4 #hvo4 ,pages ,,viii #che4 #ajj ,illustrations #c4ej ,,meade--,chemists' ,pocket ,manual4 #abmo4 ,pages ,,xii #ddd4 #ci ,illustrations #c4jj ,,moissan--,the ,electric ,furnace4 #hvo4 ,pages #aj #cje4 #da ,illustrations #b4ej ,,nikaido--,beet-,sugar ,making and ,its ,chemical ,control4 #hvo4 ,pages ,,xii #ced4 #fe ,illustrations #c4jj ,,nissenson--,the ,arrangement of ,electrolytic ,laboratories4 #hvo4 ,pages #ha4 #eb ,illustrations #a4be ,,noyes--,organic ,chemistry for the ,laboratory4 #b;d ,edition1 revised and enlarged4 #hvo4 ,pages ,,xii #bib4 #da ,illustrations #b4jj ,,noyes ,,and ,,mulliken--,laboratory ,experiments on ,class ,reactions and ,identification of ,organic ,substances4 #hvo4 ,pages #ha #j4ej ,,parsons--,the ,chemistry and ,literature of ,beryllium4 #hvo4 ,pages ,,vi #ahj #b4jj ,,pfanhauser--,production of ,metallic ,objects ,electrolytically4 #cvo4 ,pages #afb4 #ajj ,illustrations #a4be ,,phillips--,methods for the ,analysis of ,ores1 ,pig ,iron and ,steel4 #bnd ,edition4 #hvo4 ,pages ,,viii #agj4 #c ,illustrations #a4jj ,,seger--,collected ,writings of ,herman ,august ,seger4 ,papers on ,manufacture of ,pottery4 #b ,vols4 ,large #hvo4 #g4ej a vol4 or #ae4jj a set ,,stillman--,engineering ,chemistry4 #dth ,edition4 #hvo4 ,pages ,x #gdd4 #agd ,illustrations #e4jj ,,tower--,the ,conductivity of ,liquids4 #hvo4 ,pages #hb4 #bj ,illustrations #a4ej ,,venable--,the ,development of the ,periodic ,law4 ,small #abmo4 ,pages ,,viii #cba4 ,illustrated #b4ej ,,venable--,the ,study of the ,atom4 #abmo4 ,pages ,,vi #bij #b4jj ,,vulte ,,and ,,goodell--,household ,chemistry4 #bnd ,edition4 #abmo4 ,pages ,,vi #aij #a4be ,,wiley--,principles and ,practice of ,agricultural ,chemical ,analysis4 ,vol4 ,i4 ,soils4 ,pages ,,xii #fcf4 #ee ,illustrations4 #ag ,plates #d4jj ,,wiley--,principles and ,practice of ,agricultural ,chemical ,analysis4 ,vol4 ,,ii4 ,fertilizers and ,insecticides4 ,pages #fhd4 #dj ,illustrations4 #g ,plates #d4ej ,,wysor--,metallurgy1 a ,condensed ,treatise for the use of ,college ,students and ,any ,desiring a ,general ,knowledge of the ,subject4 ,pages #cjh4 #hh ,illustrations #c4jj