J 593 S94 "opy 1 Quantitative Relationships of Carbon, Phosphorus, and Nitrogen in Soils PRESENTED TO THE FACULTY OF THE UNIVERSITY OF ILLINOIS URBANA, ILLINOIS, U. S. A, AS A Thesis for the Degree of Doctor of Philosophy JUNE, 1909 BY ROBERT STEWART, B. S. PUBLISHED BY THE UNIVERSITY OF ILLINOIS AGRICULTURAL EXPERIMENT STATION AS BULLETIN No. 145 UNIVERSITY OF ILLINOIS Agricultural Experiment Station BULLETIN NO. 145 QUANTITATIVE RELATIONSHIPS OF CARBON, PHOSPHORUS, AND NITROGEN IN SOILS Bv ROBERT STEWART URBANA, ILLINOIS, APRIL, 1910 f 1« A Hi ( iTti. \y«rs I "f \j Note Ivohcrl v^tewart was born in American Fork, Utah, August 16, 1S77. Me secured his common school education in the pubhc schools of rtah. In the fall of 1896 he entered the preparatory department of the Ag-ricultural College of Utah. He graduated from this institution in June, 1902, with the degree of Bachelor of vScience. He immediately received an appointment as assistant chemist in the Utah Experiment Station. While holding- this po- sition, during the years 1902-03, 1903-04, he took graduate stu- dent work in. the college. During the school year 1904-05 he was a member of the Graduate School of the University of Chicago where he studied chemistry under the direction of Doctor Nef. In i()05 he was ap])ointed assistant professor of chemistry in the Utah College and while holding tliis position, during the years 1905-06, i9of>-0/, 1907-08, he continued his graduate student work. Dur- ing the summer of ieen the first one to sug'g'est that it consisted of other elements than carbon, hydrogen and oxygen. He separated the org-anic matter into xarious supposed pure org'anic compounds of an acid nature, which were analyzed and studied by the usual organic method. Wolff (2) determined the org-anic matter of the soil bv calcu- lation, l)v use of the factors 1.724 or 0.471 : he multiplied the or- g'anic carbon 1)y the fonner factor, or the totid organic carl)on dioxid by the latter. The factors were derived from the concep- tion tliat "Inimus" contained 5><) rep«Tte(l tlic total carbon, nitrogen and pliospli(»rns contents of a great nnniber of samples of the soils of Illinois This woik r^-, thns, made the basis of calculating the relationship of carbon, nitrogen and phosphorus reported in part (B) of this thesis. 2. Nitrogen in Soils The nitrogen in soils exists chielly as organic nitrogen with a \ery small amount of inorganic nitrogen. The organic nitrogen mav exist in some known and probably some unknown forms. Aliilder ( 1 ) beliexed the nitrogen, found in the hunuis, to be associated \\ ith the organic matter in the form of the ammoniacal salts of the \arious organic acids obtained liy him. Afiiller (4) thought he detected a tendency for the nitrogen to vary inversely as the carbon. Detmcr ( () ) believed that the nitrogen formed a dehnite com- pound with the ()rganic carbon of the soil since the nitrogeu could be liberated onlv with great difficulty and by the use of the most drastic chemical agents. Simou ( II ) believed that the organic matter of the soil pos- sessed the ])ropertv of absorbing the free nitrogen of the at- mosphere and (»f con\ertiug it into ammonia which in turn united with the organic acids in the form of their ammoniacal salts. Sos- tegni ( 10) a little later discussed tlie work of Simon and reported a series of experiments to pro\e that Simon's assumption was un- tenable. Berthelot ( K/), in iSSf>, reported the carbon and nitrogen con- ten.ts of calcareons cla\ev soil, originally very deficient in organic carlion and nitrogen but which was gradually increasing in carbon and nitrogen content owing to the action ot diatoms. Berthelot and Andre ( _'(% 74, y^^ 7^) I'der carried on a series of experiments for the i)urpose of separating the org'anic nitro- genous material into its various compounds. They reported the amount of total, nitric, amido and ammoniacal nitrogen present in the soil. Eggertz (21) differed very materially from Mulder. He con- cluded that Alulder's contention, that the nitrogen associated with the organic matter of the soil existed onlv as the ammoniacal salts (d" the \arious organic aciy Frear and Hess (54) on manured land. Dojarenko (56) recently studied the '"humic" nitrogen of soils. He determined the total, humic, amid, ammoniacal and amido ni- trogen in seven samples of Ijlack Russian soils. The results are rept^rted in Tal;)le 2. 96 Bulletin No. 145 [At^ril, T.\BLE 2.— PkkcEntage of Totai, Humic, Amido, Amid and Am:\ioniacai, Nitrogen in Humus Percent in dry substance Percent of total quantity of nitrogen No. Total humic nitrog-en 2.735 3.38 2.64 3.33 4.58 3.65 4.02 Amido nitrogen 1.34 1.81 1.30 2.34 1 . 01 1.26 1.96 Amid nitrogen Ammo- niacal nitroijen Amido nitrogen Amid nitrogen Ammo- niacal nitrogen 1 2 3 4 5 6 7 0.31 0.41 . 29 0.32 0.48 0.27 0.22 0.04 0.08 0.02 0.03 0.01) 0.07 0.03 49.09 53.55 4'».20 70.27 22.01 34.52 48.75 11.38 12.13 10.99 9.61 10. 4() 7.40 5.47 1.46 2.36 0.80 0.90 1.31 1.90 0.78 'Phis (lid mil account for all of tlic nitroj^'en present and so the (lucstion arises in what form docs the remainder exist? D'Utra (70) found that the humic nitrog-en showed wide \'ari- ations. Hilgard (71) reported the average humic nitrogen of 466 samples of soil from the humid regions as 5.45 percent, while the average of 313 samples of soil from the arid section was 15.87 percent. Later (73) he found that the average humic nitrogen for 696 samples of humid soil was 5.00 percent, while that of 573 samples of arid soil was 15.23 percent. It must he remembered, however, that the total quantity of nitrogen of the two regions is in the inverse order. The total nitrogen of the uplands and low- lands of California for example, is o. loi percent and o. loi per- cent respectixcly, while the total nitrogen of the ordinary lirown silt loam soils of the corn l)elt in Illinois varies from 0.J18 percent to 0.337 pci'cent. 3. rJlOSlMLORlTS IN Soii.s The phosphorus of the soil ma\' exist in the inorganic and organic condition. The greater part is in the inorganic form with an unknown amount in the organic state. The form and amount of the organic phosphorus is uncertain, and, indeed it has been questioned, especially during recent years, whether or not organic phosphorus occurred in the soil to any appreciable extent. Milkier ( i), as early as 1844, noted that the organic material was not readily freed from phosphorus. The work of Thcnard, Schutzenber (5, 6, 7) showed that union may take place between various forms of artilicial humus and phos- l)hates under certain conditions and indicated that combination may possibly take place in the soil between organic carbon and inorganic phosphorus. Detmer (9) in the preparation of his "pure humic" acid, noted /p/o] Carbon, Phosphorus and Nitrogen in Soils 97 that the material could be freed from phosphorus only with great difficulty. Grandeau (lo) regarded the phosphorus associated with the extracted matierc noire as being of the greatest importance, and, was probably in special combination with the org^anic matter. ITe regarded it as an index of the fertility of the soil. Sinion (ii) believed that he had demonstrated that miion took place between organic matter and phosphates. When freshly pre- cipitated humic acid was suspended in water and digested with calcium phosphate and then filtered, the filtrate showed an excess of phosphoric acid : this excess, he concluded must be in union with the organic matter in solution. He thought that a double com- pound of ammonia and phosphorus existed in the soil. Schultz (12) showed that the addition of humus to "Basalt- boden" increased the absorption al)ility of the soil for phosphates. Eichhorn (13) repeated some of Simon's work and concluded that organic cohibination did not take place as indicated by Simon but that the humus had decomposed the tri-calcium phosphate with the fomiation of acid phosphate. Pitsch (14) determined the solubility of the various mineral phosphates, including iron and aluminium phosphates, in a solu- tion of auiuwn'unn luiniatc itself. He concluded, that, since this solution exerted a solvent action on mineral phosphates, the am- monia extract of the soil contained phosphorus, other than that originally associated with the organic matter in the soil and prol)- ably part, at least, of the ammonia soluble phosphorus was derived from the iron and aluminium phosphates. M. P. DeGasparin (15) found in calcareous clav soil five per- cent of the total phosphorus in organic combination. He noted, furthermore, that the mosses and lichens contained from 5 to 6 times as much phosphorus as the rocks on which they grew ; the soil formed therefore, from tlie debris of these plants should be relatively richer in phosphorus and should have a part of its phos- phorus in combination with carbon in the organic material. Eggertz (21) found that the ammoniacal extract of the soil, when treated with an acid, formed a precipitate of organic matter which always contained phosphorus. He concluded, therefore, that part of the phosphorus of the soil w^as united to the carbon in or- ganic combination. Later, Eggertz and Nilson demonstrated that the amount of phosphorus soluble in dilute mineral acids showed a marked in- crease after ignition of the soil. Ignition rendered 10 times as much phosphorus soluble in 2 percent hydrochloric acid. They attributed this to the destruction of the organic matter which had held the phosphorus in combination which would not vield up its phosphorus to acids. 93 Bulletin No. 145 [AprU, Van Bemmelen (23) believed that the ir-ei"tz, were not originally chemically combined to carbon in the ori^-anic matter of the soil but were al)s<)rbed by the precipitated oelatiuous iiuilicrc Jioirc. According- to X'an r.emmelen the i)h()s- phorus existed in the soil ])rincipally as calcium ])h(>sphate with a verv small quantity occurriug in the alj-orhcd state in the torm of a colloid al 01 I'liiiiiatc-Silicot-Koiiit'h'.v. Two questions seemed to be of parauiount impurtance to Wik- luud (JS) regardini;- the work of Kg-o-ertz : hrst, was the amount of the ammonia-soluble phosphorus obtained from different soils constant? v^econd, did the |)hosphorus exist in the mullk()rpers (Iiiaticrc noire of Grandeau ) in chemical com1)ination with carl)on, or simply as absorl>ed phosphorus? lie concluded that there was a tendency for the ammonia-soluble phosphorus to be constant in different soils. lie showed, further, that one digestion with 12 percent hydrochloric acid did not completely remove all of the acid soluble phosphorus, ])ut a second and e\en a third digestion still remo\-ed some phospliorus. Xow, he reasoned, if the phos- phorus removed by the second and third digestion was simply ex- tracted fr(_»m the absorl>ed ])liosphorus, extraction of the soil with ammonia after the iirsl dig"estion with hydrochloric acid, should yield a solution of iiiaticrc noire containing a higiier phosphorus content than when the soil was conq)letely extracted with the hy- drochloric acid. Such, however, was not the case, therefore, the phos])horus did not exist as absorbed phosphorus and must be in coml)ination with carbon in the organic matter. Snyder (34) noted that some phosph()rus, iron, etc., were ex- tracted' with the iiialicrc noire lint he did \vA seem to think at this time thai lliere was an\- e\idence of coml)ination with carbon. About the same time he ol)served the rapid loss of phospliorus as- sociated with the humus in continuous cnhi\ated soil. According to P.erthelot and Andre ( .7) phosphorus may be found in the soil (a) in inorganic or mineral ])hosphates, (b) in organic ethers and (c) in oiganic or mineral com[)ounds not read- ily decomposed. Schmoeger ( J() ) re\ iewed the rival claims of Eggertz and Nil- son, and Wiklund on the one hand, and Van Bemmelen on the other, regarding the phenomenon of ignition rendering the phos- ])horus of peaty soil more readily soluble in acids. It seemed possible to Schmoeger that the soil might possess such a tenacious absorbent power (or jjlmspliorus that it would not vield u]) its ])h. )S])horus to acid treatment before ignition. But he deduced experimental exidence to show that such was not the case. ipio] Carbon, Phosphort's and Nitrogen in Soils 99 Digestion of the soil itself and also the extracted inatlerc noire with a solntion of potassinni h_\drogen phosphate failed to add any phosphorus which was not again recovered hy treatment with liydrochloric acid. This was conclusive evidence to Schmoeger that the phosphorus did not exist as absorbed phosphoiiis and must, therefore, exist in organic combination. Two possibilities sug- gested themselves to Schmoeger : first, the phosphorus existed in the form of lecithin; second, it existed as nuclein. Lecithin was found to be present only in traces. The characteristic property of nuclein to "split-off"' its phosphorus in the form of phosphoric acid, when heated, under pressure in the presence of water, to* a temperature of 150°-! 60° was utilized by Schmoeger. The soil under examination, treated in this way, yielded as much soluble phosphorus as did the ignited soil. This experimental evidence led him to conclude that nuclein or some closely allied bodies were present in the soil. Later Schmoeger (39) cc^nfirmed his previous work and pro- duced additional evidence in fav(M- of his view that nuclein or simi- lar bodies existed in the S()il. Tal)le 3 shows some of the results obtained. Table 3. — PercenTagk of Sui^kuric Acid and Phosphorus Soluble in Dilute Acid Percent Soil in original state 0.122 0.043 Evaporated soil 290 0.083 Ignited soil 0.939 0.095 Since sulfur is regarded bv many authors as being a constitu- ent of plant nuclein, the increased solubility of this substance to- gether with the phosphorus when the soil was treated as indicated above, was reg'arded as evidence in favor of his assumption. In a later article (40) he .showed, by similar treatment, that analogous bodies existed in the moor grass out of which the moor soil was formed. Tliis was regarded as additional exidence in favor of his view. Tacke (33) observed that the drying out of soil rendered the phosphorus available. There were three possible explanations sug- gested to him: first, the phosphorus existed in the soil in organic coml)ination which was destroyed l>v the process of drying; second, it existed in the soil in the. colloidal form as suggested by Van Bem- melen ; third, the drying out of the soil gave rise to substances of a strong acid nature which acted upon the insoluble phosphorus compounds rendering the phosphorus soluble. 100 Bulletin No. 145 [April, In a later article (42) he showed that very little water soluble phosphorous existed in the soil under consideration, but that dry- ing at 70°-8o° rendered o\'er 50 percent of the total phosphorus soluble in water. Snyder (36) repi^rted results of a confirmative nature regard- ing the phosphorus associated with the humus in virgin and cul- tivated soils. Later he (37,41) studied the product obtained by the conver- sion of known substances, under known condition, into humus. The ash of the uiaticrc noire obtained from this material contained phosphorus, among other substances, and according to Snyder : "There is every indication that these elements are in organic com- bination with the carbon, hydrogen and oxygen of the humus." As regards the question whether or not the humus united with the inorganic phosphorus of the soil, he concluded that his experi- mental evidence showed that such union did take place. Nannes (49) found that a well decomposed peat soil contained 0.166 percent pliosphorus. He found that 0.057 percent of phos- phorus was extracted with the uiaticrc noire. When the ammonia- cal solution of the uiaticrc noire was treated with hydrochloric acid, 0.039 percent of the phosphorus was found in the organic precipi- tate. He also attempted to isolate a definite organic phosphorus compound and he l)elieved that he detected the presence of lecithin and chlorophyllan. Ladd (43) found in a study of eight samples of ditYerent soil that an average of 41 percent of the phosphorus was associated with the extracted niaticre noire; the variation, however, was from 10 percent to 90 percent. In a later article (44) he showed that as the humus of the soil increased the phosphorus associated with the extracted uiaticrc noire also increased. From the fact that the organic precipitate, fonned by neutralizing the ammoniacal extract, contained the phos- phorus he concluded that it existed in the soil in organic combina- tion, but just what the relationship was not clear. Emmerling (52) believed that there were four forms of phos- phorus in the soil, one of which was phosphorus in organic com- bination. Rimbach (53) found 6.15 percent P2 O5 in the ash of the maticrc noire which was precipitated from the ammoniacal solu- tion by the addition of gypsum and magnesium sulfate. Nagaoka (57) found that ignition of the soil for fifteen min- utes at a faint red heat materially increased the availability of the l)hosphorus. He attributed this action to the destruction of the liuniopliosphates. I9I0] Carbon, Phosphorus and Nitrogkn in Soils 101 Aso (58) continued, in a i;-encral way, the rcsnlts obtained by Schmoeger. He also found 0.049 percent of lecithin in the soil. He drew the following- conclusions: 1. Phosphorus existed in the soil as inorganic and organic compounds. 2. The organic phosphorus material was principally nuclein with a very small part of lecithin. 3. Ignition rendered the phosphorus in organic coml)ination available. Hart well and Kellogg (60) found that an axerage of one-half of the phosphorus was associated with the organic matter in the soil taken from four plots which had received different treatment. Dumont (62) studied a complete manure, the composition of wdiich was as follows: soluble matter (in dilute alkali) 50.4 per- cent; insoluble matter 49.6 percent; total nitrogen [.6 percent; total phosphorus 1.27 percent. The solul)le portion contained 35 percent nf the nitrogen and 46 percent of the phos[)horus. In order to obtain data u[)on the state of combinatiitn of the phosphorus, the amnioniacd solution of matiere noire was treated with various reagents with~the result (recalculated to the element basis) shown in Table 4. Table 4. — Distribution of Phosphorus When Matiere Noire is Precipitated Precipitatiiijir aj^etil Citric acid Hydrochloric acid. Ferric chlorid Aluminium sulfate Calcium chlorid... Phosphorus In precipitate In filtrate 0.383 0.386 0.532 0.566 0.5S4 203 0.199 0.053 0.019 0.0009 These results furnished conclusive proof to Diimont that a part of the phosphorus of the soil was in organic combination. Later (64) he obtained better cultural results from application of humic phosphatic manures than from mineral phosphatic ma- nures and better even than from barnyard manure, which he at- tributed to the phosphorus in organic combination. In a still later article (65) he said that the organic phosphorus was derived from two .sources: first, from the nuclein and lecithin of the decaving vegetable and animal debris; .second from the union of the humus with the water soluble phosphates of the soil. Evidence of the latter contention was ol)tained by precipitating the matiere noire in the presence of potassium hydrogen phosphate by different reagents as indicated in Table 5. 102 Bulletin No. 145 [Atfii Table 5. — Amount ok PhOvSphorus in Pkecipitatrd Humus and Filtrate Series A Phosphorus in- troduced=.087 Series B Phosphorus in- troduced = .218 Series C Phosphorus in- troduced= .437 Precipitatiiii; agent Phos- phorus in humus Phos- phorus in tiltrate Phos- phorus in humus Phos- phorus in filtrate Phos- phorus in humus Phos- phorus in filtrate Acetic acid Citric acid Hydrochloric acid Sulfuric acid 0.056 0.054 0.0.57 0.057 0.031 0.033 0.030 0.O30 0.057 0.055 0.05*» . 061 0.160 0.163 0.158 0.156 0.058 0.054 0.059 0.062 0.374 0.381 0.378 0.372 Altho the amount of dipotassiuni phosphate added to the sohition had increased, tlie amount of phosphorus absorbed by the liumus was practically constant, due to the fonnation of detinite "composes phospho-humicjue." KcMiig- (67) found that hydroi^'en peroxid oxidized from 40 l)ercent to 70 percent of the humus present in the soil and that much more of the phosphorus was soluljle in pure and carbonated water aftei^ oxidation than before, due, he believed, to the destruc- tion of the organic phosphorus compounds. Fraps (69), quite recently, made a study of the phosphorus extracted from the soil by 4 percent ammonia in the usual deter- mination of humus. Tie conhrmcd Pitsch's results regarding- the possibility of some of the ammonia-S(^lublc pliosphorus being of inorg^anic orig'in. He separates tlie ammonia-soluble phosphorus into three classes as follows: 1. The phosphorus associated with the clay held in suspension in the liquid. 2. The phosphorus precipitated with the organic matter when the sr)]ution was neutralized with an acid. ,V The phosphorus which remained in solution after the pre- cipitation of the organic matter. With the soils under consideration he found that i ^9 of the ammonia-soluble phosphorus was in the lirst class, 1/3 was in the second class and 5/0 was in the third class. The phosphorus found in the first class was assumed to be as- sociated with tlie clay particles as iron and aluminium phosphates. He concluded that the phosphorus precipitated with the organic matter from the ammonical solution by the addition of acids was in organic combination. The phosphorus remaining in the mother liquor was assumed to be derived from the iron and aluminium phosphates of the soil. Mooers and Hampton (y-) recently proposed a method for obviating the error introduced in I he humus determinations by the ipio] Carbon, Piiospiiorus and Nitrogkn in Soils 103 suspended clay. They claimed that filtration throug-h the Cham- berlain-Pasteur iilter, as suggested by Cameron, introduced a serious error inasmuch as the filter absorbed some organic matter. They proposed an evaporation method : by evaporation of the ammoniacal extract to dnaiess re-dissolving in ammonia and filtra- tion, several times, a perfectly clear solution was obtained. Deter- mination of the humus in this filtrate gave very concordant results. Hopkins and Pettit (68) found that in certain soils the mineral composition had a tendency to be constant in the surface, sub- surface, and subsoil. This was indicated by the unifonn potassium content of the surface, subsurface, and subsoil and by the fact that dift'erent samples of surface soil of the same type showed a wide variation in the phosphorus content but that this variation largely disappeared in the subsoil. The potassium exists in the soil in the inorganic form, the nitrogen exists chiefly in the organic form while the phosphorus may exist in the inorganic and organic state. They suggested, therefore, a method for calculating the phosphorus in the organic state in the surface soil. The difference in amount of nitrogen in the surface soil and subsoil, and the difTerence in the amount of phosphorus in the surface soil and subsoil gave appar- ently the amount of nitrogen and phosphorus associated together in organic combination. By means of this ratio and the total amount of nitrogen in the surface soil tlie total amount of organic phosphorus present in the surface soil could be calculated. 4. Carbon and Nitrogen Content of Fundamental Rocks The fundamental rocks out of which soils have been formed contain an apprecial)le amount of carbon and nitrogen which is in- digenous to them. Dellese (3) discovered that mineral matter, crystalline, sedi- mentary and eruptive contained carbon associated with nitrogen. This mineral matter, which was formed under similar conditions of temperature, pressure, etc., had a tendency to contain a constant amount of carbon and nitrogen. The work of Lawes and Gilbert (16), Dyer (55) and Hall and Miller (66) on the clays and other fundamental rock material taken from various great depths indicated that an appreciable amount of carbon and nitrog'en was indigenous to the underlying soil material. IQIO] Carbon, Phosphorus and Nitrogen in Soils 105 (B) EXPERIMENTAL PART The starting point of snch an investigation consists of a con- sideration from a mathematical point of view of the existing- data reg'arding tlie relationships of carbon, phosphorus and nitrogen of the soil. I. Mathematical (a) INEI.UKNCK OE AGE ITPON THE NlTROf.EN-CARBON RATTO From the data availaljle in the literature it is possil)le to deter- mine within certain limits the intlnence of age upon the nitrogen- carbon ratio in soils. From the average results of a number of nitrogen determinations (68) and the carbon content obtained by calculation fr(_»m the proximate analysis, it is possible to determine the approximate nitrogen-carbon ratio in the more common humus producing materials. The results obtained in this way will be foiuid in Table 6. The materials naturally fall into tv/o groups: in the first gi'oup the ratio varies from i :^2.2 for corn stover to I 184. 1 for wheat straw; in the second group the \ariation is from I nf)./ for alfalfa hay to i :35.4 for timothy hay. Table 6. — Approximate Nitrogkn-Carbon Ratio in the More Common Humus Producing Materials Kind of material Corn stover. Oat straw. . . Wheat straw Timothy hav, Clover hay. . . Cowpeahay. , Alfalfa ha3'. . Albumin ... Zein Nuclein .... Carbon tol of nitrogen 52.2 67,8 84.1 35.4 21.3 19.5 16.7 32 3.4 In Table 6 will also be found the nitrogen-carbon ratio in some of the compounds which might be expected to be found in humus. The ratio is very narrow and does not vary much from i :3. The next step in the study in the influence of age upon the nitrogen-carbon ratio would l)e to determine the ratio in as fresh humus as possible from known materials. Snyder (35) in his studv of the production of humus from known materials placed a weighed quantity of the material together with a weighed quantity 106 Bulletin No. 145 [April, of soil having a low humus content in a bux and set aside for one vear. At the end of the experiment the humus was extracted and the carl)on and nitrogen determined in the inuticrc noire. At first thought this would appear to furnish the desired information, but unfortunately no check was run with the untreated soil, so no cor- rection can be made for the carbon and nitrogen which may have been converted into humus from the unhumified material of the soil. This i^ evidently not a cpiantity which can be ignored since the humus C()ntent of the original soil is .06 percent while the total nitrog'en of the soil is .02 percent showing that considerable un- humified organic matter was present, otherwise the humic nitrogen would be 33.33 percent while it has been shown (71) that the luimic nitrogen would more probal)ly be nearer 5 percent. In ad- dition, the fact that the humus obtained from sugar contains some nitrogen is evidence that some of the unhumified organic matter of the soil has been converted into humus, since sugar does not con- tain nitrogen. The results, however, will be found in Table 7. In Tabi,e 7.— Minnesota Soii< Studies: Humus Pkoduction From Known Materiai^s Percent Ratio of Material used Humus Carbon in humus Nitrogen in humus carbon to 1 of nitrogen Original soil , 0.06 0.58 0.37 0.31 0.46 0.47 41.«t5 54 . 22 48.77 54 . 30 51.02 ? 6.16 8.24 10.96 2.50 5.02 ? Cow manure Clover 6.8 6.6 4.5 Oat straw Flour .... 21.7 10.2 Saw dust Sugar .... 0.59 0.32 49.28 57.84 0.32 0.08 153.8 741.0 the first five substances the variation is from i :2i.7 for oat straw to I :4.5 for meat scraps. The large number of carbon and nitrogen determinations made in the soils of Illinois (68) rendered it possible to determine the nitrog'en-carbon ratio, not only for the surface soil, Ijut also for the subsurface and subsoil. The average of 19 determinations for the soil type, gray silt loam on tight clay, gave the ratios i :io.4, 1 :8.8, and i 17. 6 for the surface, sul)surface, and subsoil re- spectively. The ordinary brown silt loam soils as an average of 68 determinations gave a nitrogen-carbon ratio of 1:12.1, 1:11.5 and 1 :8.9 for the surface, subsurface, and subsoil respectively. The 1)lack cla)' loam soils as an average of 25 determinations g^ave 1 :ii.7, I :ii.<) and 1 :f) respectively in the surface, subsurface, and subsoil, 'i'hc peat soil as the average result of 5 determinations gave I :ii.8 and t :i2.9 for the siu^face and subsoil respectively. ipio] Carbon, Phosphorus and Nitrogen in Soils 107 Tabi,e 8 —Ratios ok Carbon and Nitrogen in Ii^i^inois Soii^s Soil type No. Soil types No. of analysis on which calculations are based Carbon to 1 of nitrogen Surface Sub- surface Subsoil 330 426 526 626 726 1126 1026 Gray silt loam on tight clay Brown silt loam Brown silt loam Brown silt loam Brown silt loam Brown silt loam Brown silt loam 19 11 8 6 4 30 9 10.4 12.5 13.2 11.4 11.9 11.9 12.0 8.8 11.7 12.9 10.5 11.1 11.5 11.5 7.6 9.6 8.7 8.7 8.8 8.6 9.3 Averages 68 12.1 11.5 8.9 420 520 1120 1220 Black clay loam Black clay loam Black clay loam Black clay loam. . . . 7 5 11 2 12.2 12.4 11.1 11.2 12.2 12.2 ll!l 12.2 8.9 11.4 8.3 7.4 Averag-es 25 11,7 11.9 9.0 1401 Deep peat 5 11.8 12.9 12.9 The Rothamsted work furnished information regarding the nitrogen-carbon ratio of the soil in nine inch sections to a depth of 90 inches. These resnUs will be found in Tables 9 and 10. The ratio for the Broadbalk wheat fields varies from i 19.5 to 4.8 for the surface and ninth 9 inches respectively. After the fifth 9 inches there is very little change in the ratio. In the Hoosfield barley soils the ratio varies from i :io.6 to i :8.8 for the surface and sub- soil respectively. Tabi,e 9.— Broadbalk Wheat Soils: Ratio of Carbon to Nitrogen Depth First 9 inches (all plats) Second 9 inches Third 9 inches Fourth 9 inches Fifth 9 inches Sixth 9 inches Seventh 9 inches Eighth 9 inches Ninth 9 inches Tenth 9 inches Percent Carbon 1.155 .640 .492 .339 .279 .256 .248 .215 .189 .188 Total ni. trogen .1222 .0784 .0666 .0511 .0472 .0430 .0420 .0396 .0391 .0375 Carbon to 1 of nitrogen 9.5 8.2 7.4 6.6 5.9 5.9 5.9 5.4 48 50 Table 10 — Hoosfield Barley Soils: Ratio of Carbon to Nitrogen Depth Carbon to 1 of nitrogen First 9 inches 10 6 Second 9 inches 8^8 Third 9 inches 8 8 108 Bulletin No. 145 [April, Hall and Miller (66) reported the carbon and nitrogen con- tent, and ratio of carbon to nitrogen in samjiles of \-aric)ns ma- terials taken from such great de[)ths as to preclude all possibility of weathering. Since the nitrog'en was always found to be associ- ated with carbon it w^as regarded as being of organic origin and as being deri\ed in part from the organic matter present in the clav at tlie time of its deposit. These results are shown in Table ii. TabIvE 11. — Carbon and Nitrogen in UnweaThered Rocks No. of soil 3 4 5 (» 7 8 9 10 11 12 13 14 Formation Lower Bag-shot Sand, Weybridg-e. . Upper Greensdiid, Farnham, Surre}' Folkestone Beds, Brabourne, Kent. Lower Greensaud, Sevenoal^s London Clay, London Gault Clay, Nackholt, Kent Weald Clay, Pluckley. Kent Caiboniferous Shale, Barnsley... Lower Gault, Dover Oxford Clay, Dover Kimmeridge Oay, W^elton Lines. . . Kimmeridge Cla3', Dover Lower Lias, Micketon, Glos Clay with Flints, Harpenden Ueptb at whichsani- ple was ta- ken, ft. Percent Organic carbon 18 20 30 20 30 130 18 30 1236 280—400 920 246 570 700 10 0.02 0.032 019 0.076 391 427 135 1.938 0.172 0.548 2.139 0.387 1.120 577 Nitrogen .00384 .00718 .00453 .00881 .041 .0415 .0647 .137 .0325 .0528 .107 .0455 .0803 .0294 Ratio 5.4 4.5 4.2 8.7 9.5 10.3 2.1 14.1 5.3 10.4 20.0 8.5 13.9 19.6 NOTES 1. A grey coarse sand. 2. Pale g:rey tine sandy rock. 3. Coarse yellowish sand. 4. Fine yellowish sand. 5. Solid grey clay. (). Solid dark green clay. 7. Close grey and red mottled clay. 8. Hard gre^' shale. 9. 10, 12. Hard grey clays from the coal pit shafts at Dover. 11. Hard grey clay. 13. Hard grey clay. 14. Reddish sandy brick earth. It will be seen from a study of the abo\e tal)les that normal conditions the nitrogen-carbon ratio ot the soil has ency to become narrower as the age of the organic mater creases. 'J'he i-atio, howe\er, ne\er becomes narrower ( ei|ual to the ratio of the more common proteins contained humus i)roducinu' materials. under a tend- ial in- )r ever in the (b) CARHON, NITR()('.i;m ANI:) PlIoSl'llROtTS IX TIJJNOIS SOII.S IJefore discussing the ])hosphorus-carbon and ])h(^sj)horus- nitrogen ratios in the soil it seemed desirable to determine as closely as possible these ratios in fresh material out of which humus mig^ht be formed. IQIO] Carbon, Phosphorus and Nitrogen in Soils 109 Table 12. — Approximate Carbon-Phosphorus and Nitrogen-Phosphorus Ratios in the More Common Humus Producing Materials Kind of material Carbon to 1 of phospho- rus. Nitrog-en to 1 of phos- phorus Corn stover 417 8.0 Oat straw Wheat straw 420 525 6.2 6.2 Timothy hay Clover hay Cow pea hay 283 171 181 186 8.0 8.0 9.3 Alfalfa hay 11.1 Nuclein 3.7 1.4 The ratios in the more common humus producini^- materials calculated from the average of a numl)er of analysis for nitrogen and phosphorus (68), will l)e found in Ta])le u. In the coarser material the phosphorus-carbon ratio varies from 1:417 to 1:525: the phosphorus-nitrog'en ratio is more constant being i :6.2 and 1 :8. In the hays, the phosphorus-carbon ratio varies from i :i86 to i :283 while again the phosphorus-nitrogen ratio is more constant, the variation being i :ii.i to i :8. In nuclein tlie ratios are i 13.7 and I :i.4 respectively. In Table 13 will be found the phosphorus-carbon and phos- phorus-nitrog'en ratios obtained by calculation from the Minnesota Soil Studies. The phosphorus determinations which were reported as phosphoric anhydrid were first recalculated to the element basis. Both ratios, it will l)e observed, are \er)- narrow. In Table 14 will be found the pho.sphorus-carbon and phos- phorus-nitrogen ratios in Illinois soils calculated from the data re- ported by Hopkins and Pettit (68). The average of 7 calculations of the gray silt loam on tigiit clay ga\e the phosphorus-carbon and phosphorus-nitrogen ratios as i :42.6 and i :i3.8 respectively. Table 13.— Minnesota Soil Studies: Carbon-Phosphorus and Nitrogen- Phosphorus Ratios Kind of material Original soil Cow manure Clover Meat scraps Oat straw Flour Sawdust Suffar Carbon to 11 Nitrogen to of phospho-j 1 of phos- rus. phorus 9.8 11.2 9.7 38.2 22.0 37.0 42.4 1.4 1.7 0.24 0.06 110 Bulletin No. 145 [April, Table 14. — Illinois Soils: Okc.anic Phosphokus; Ratios of Carbon to Phosphokus, Nitkogkn to Phosphorus and Carbon to Nitrogen, Factors kor Calculating the Organic Phosphorus. Number of aii- alysisoii which calculations are based Organic phos- phorus as per- cent of total phosphorus Ration of Factors for calculating the organic phos- phorus from the organic carbon Soil type No. Carbon to 1 of organic phosphorus Nitrogen to 1 of organic pliosphorus 330 7 24.4 142. 13.8 0.007012 426 526 626 726 1126 1026 9 8 5 4 24 9 34.4 29.5 13.9 38.1 40.9 44.9 132. 185. 298. 133. 116. 125. 10.6 14.0 25.1 10.5 9.9 10.9 0.007570 0.005393 0.003348 0.007491 0.008583 0.007988 Average 59 33.5 165. 13.5 0.006053 420 .520 1120 1220 7 5 11 2 36.0 33.8 46.2 32.4 134. 260. 90. 169. 10.3 12.0 8.3 15.2 0.007441 0.00383() 0.005907 0.002956 Average 25 37.1 163. 11.4 0.006113 1401 1401 4 (b) 5 100.0 100.0 230. 338. 19.6 26.5 0.004311 O.00295<) (b) Subsoil (7" 40") The ordinary brown silt loam soils, as an average of 59 deter- minations, g-ave the ratios of i 1165.2 and i :i3.5 respectively. The lilack clay loam soils, as an average of 25 calculations, gave the ratios of i 1163 and i :ii.4 respectively. The ratios in the surface peaty soil, assuming all the phosphorus to be in the organic state, are i 1230 and 1 :i(;.6. The ratios in the subsoil of the peaty soil are somewhat wider, l>eing i 1338 and i :26.5 respectively. (c) FACTORS I'OR CALCULATING ORGANIC PHOSPHORUS By means of the carbon-phosphorus ratios established as in- dicated aboxe, it is possible to develop factors for calculating the amount of the org-anic phosphorus in the surface soil from the total organic carbon. For example the carbon-phosphorus ratio, I :i63, in the black clay loam soils means that for every part of organic phosphorus there are 163 parts of carbon or for each part of organic carbon there are 0.0061 13 parts of organic phosphorus. Hence by multiplying the amount of organic carbon by the latter number the amount of organic jihosphorus may jje obtained. The factors as developed will be found in the last column of Table 14. It is hoped that they will be of value in drawing broad general conclusions regarding organic phosphorus of the soil from a numl>er of analyses. The variations in the various samples con- sidered in any single type are too great to permit the utilization of the factors in isolated cases. JQIO] Carbon, PHOsriioRUs and Nitrogen in Soils 111 • It will be observed that from 1/4 to 2/5 of the total phos- ])horiis of the several soil types considered is in organic combina- tion. These results indicate that a larg'er amount of phosphorus is in org-anic coniliination than the work of some American inves- tigators would lead us to believe. 2. Chemical (a) ANATA'TICAI, RKSUT/rs OF SOIL, FROM TTJJNOTS SOUTH F.XPFRI- MFNTAL FARM A sample of soil iov a study of the (Organic phosphorus, by the available methods for the determination of the organic phosphorus of the soil, was obtained from the Illinois South Experimental Farm. This soil is the ordinary brown silt loam soil of the corn belt. The total potassium, carbon, nitrogen, and phosphorus in the surface and subsoil were determined l)y the methods adopted by the Illinois Experiment Station. The results, expressed as pounds per two million pounds of dry soil, will be found in Table 15. The average potassium content of 36,700 pounds, and 37,070 pounds in the surface and subsoil indicate a constant mineral composition, hence the calculation method may be safely applied for the deter- mination of the org'anic phosphorus. The amount of organic phos- phorus, the various ratios and the developed factor will be found in Table 16. It will be seen that 46 percent of the total phosphorus in this soil is in organic combination. Tabi,E 15. — Anaia'Tical Rksults of Soii. from Ii,i^inois South Experi- mental Farm: RESut,TS Expressed as Pounds in Two Mihion Pounds of Dry Soii. Soil No. Soil stratum Potassium Carbon Nitrogen Phos- phorus* lA IB Average 3A 3B Average Surface Surface Surface Subsoil Subsoil Subsoil 36280 37120 36700 36600 37540 37070 41800 42180 41.90 3760 3844 3802 1735 1680 1708 938 901 919* 702 670 686 *I,ater inspection of tlie strip of land from which this sample was taken led to the conclu sion that it may have been modified by a previous disturbance of the soil in putting- in tile drainag-e; and aconiposite sample was subsequently collected at points a short distance from the tile drain which showed 'J85 pounds of phosphorus instead of 'n'> pounds. The possible influence of this difference should be kept in mind. Thus the percent of total phosphorus in organic form would be reduced from 4t) percent to 43 percent.— C. G. Hopkins. 112 Bulletin No. 145 [April, Table 16. — Organic Phosphorus: Ratios of Carbon to Organic Phos- phorus, Nitrogen to 1 Organic Phosphorus, Carbon to Nitrogen IN Surface Soil Pounds of organic phosphorus Organic phosphorus as percent of total phosphorus Ratios of Factor for calculating the organic phosphorus from organic carbon in two million pounds of soil Nitrogen to 1 organic phosphorus Carbon to 1 nitrogen Carbon to 1 organic phosphorus 423 46.0 9.0 11.1 99.2 0.01008 (1)) I'lK^Sl'IIORUS ASSOCIATKl) WITH TllK MATIERK NOIRK Of the two a\ail;i1)lc melliock for (leterniining the organic ])hosphoriis, the one, tlie determination of the phosphorus associ- ated with the iiialirrr )ioirc extracted from the soil Iw 4 percent ammonia, has given rise to some confusion. Grandeau (10) re- garded the phosphorus extracted with the iiiatii-rc noire as being probably in organic combination. Kg"gertz (^i), Nilson (79), Wiklund (J5), Dnniont (O5), Ladd (43) and Snyder (41) also regarded it as organic in form. Pitsch (14) and Van Bemmeleii (23) took the opposite view. I'itsch thought that part of the ex- tracted phosphorus may ha\e been derived from the inorg'anic phosphates of the soil. \'an Bemmelen regarded the phosphorus precipitated with the iiiaiicrc noire as absorbed phosphorus. Quite recently, Fraps {(nj) concluded that onl_\- 1/3 of the phosphorus ex- tracted Ijy ammonia was in organic conil)ination, wdiile still later vStoddart (80) concluded that only 15 of the extracted phosphorus was in organic combination. As a result of this contiicting evi- dence there is considerable C(»ntusion regarding the nature of the phosphorus extracted by ammonia. One cause of this confusion, no doubt, is the dithculty of getting rij of the suspended clay, — ordinary filtration will not remove it. ( )b\iously all of the phos- ])horus associated with the sus])ended clay should not l)e included with the organic phosphorus, altho part of it may l)e organic in form. Fraps renn)\ed the clay l)y precijjitation \\\\\\ ammonium suit ate. There is no evidence, however, that this reagent does not also precipitate some organic matter either chemically or me- chanically. Ammonium sulfate is used by physiological chemists to precipitate the proteins in order to make certain group separa- tions, while some preliminary work here show-ed that complete saturation of the ammoniacal extract of the soil with ammonium suit ate, alter the remo\'al of the suspended clay, produced a heavier ([ualitativc prcci])itate of organic matter than did the addition of hydrochloric acid, ft would seem, therefore, that the evaporation method of Hampton and Alooers (yy) is more desirable for the ipiO] CaKBOX, PllOSl'llORUS AND NlTKOGEN IN SulLS 113 removal of the suspended clay. Unless otherwise stated tlie latter method was used for the removal of the suspended clay in all the work reported in this paper. Owing to the contiictino- evidence regarding- the phosphorus as- sociated with the extracted iiiaticrc noire, it seemed desirahle to do some work with this material other than the simple determination of the phosphorus. The soil, \\ithout previous treatment with hydrochloric acid to remove the calcium, w^as extracted with 4 percent ammonia in the ratiO' of i part of soil to 50 parts of ammonia water for 36 hours as in the usual humus determinations. The clay was removed by evaporation and the iiiaticrc noire was obtained in quantity for study. Conditions here are such that the maximum quantity of in- organic phosphorus should be found in the ammoniacal extract since none has previously been remoxed l)v treatment with a min- eral acid as in the usual humus determinations. The suspended clay removed by evaporaticMi was analw.ed for carl)on and phosphorus with results as follows: Carbon ^.y;^ per- cent and 3.61 percent, or an average of 3.67 per cent; phosphorus o. 118 percent and 0.109 percent, or an average of o. 113 percent. Since the carbon in the original soil was only 2.09 percent wdiile the pho.sphorus was .046 percent, the relative increase of carbon and phosphorus in the suspended clay indicates undoul)tedly the accumulation of organic matter with the "clay." It would appear probable that the grinding of the sample of soil, while preparing it for analysis, would con\ert the organic matter into an im- palpable powder wdiich would ha\e a tendency to remain sus- pended in the li(|uid tog'ether with the fine clav particles when the soil was extracted with ammonia. The amount of the extracted niaticrc noire \\as determined. It was then analyzed for carlion, nitrogen, and |)hosphorus. The carbon was determined b\' the method suggested by Pettit and Schaub (59). The total nitrogen was determined by the regular Kjeldahl method ; correction was then made for the absorbed am- moniacal nitrogen by determining the latter in a separate sample by distillation with magnesium oxide. The phosphorus was de- temiined by igniting a sample of the inatiere noire and treating the ash with aqua re.gia; the silica was removed bv evaporation and the phosphorus determined bv the usual \olumetric method. A confirmatory test made by detennining phosphorus l)y fusion with sodium peroxid gave 0.835 percent and 0.815 percent phosph(M-us in the inatiere noire while the method adopted ga\e 0.860 percent and 0.830 percent. The results obtained expressed as poiuids per two nn'llion pounds of soil are recorded in Table 17. 114 Bulletin No. 145 [Atnl, Tablk M.—Mafihr A'ain-, Carbon, Nitkogkn and Phosphorus in the MatierE Noire; Resui.ts Expressed as Pounds per two Million Pounds ok Dry Soil. (Soil not acid-extracted before treatment with ammonia) Number Matihr Noire Carbon in the Ufatihr A'oi'rr Nitrogen in the /l/afiar Noire Phosphorus in the jMatihr Noire A B 27600 28600 10870 10850 1642 1662 233 242 Averag-e 28100 10860 1652 238 Phosphorus-nitrog-en ratio = i :6.9 Nitrogen-carbon ratio = i :<">.6 Phosphorns-carl)oii ratio = i :45.6. The uiaiicrc noire was now redissolvcd in dilnte ammonia, an excess of i percent hydrocliloric acid added and set aside over night. The precipitate of organic matter was l)roiight on to a filter paper, which had previonsly been dried at itoX and weighed. The precipitate was washed with i percent liydrochloric acid, dried at iio°C and weighed. The precipitated iiiatirrc noire was olitained in ciuantity and analyzed for carbon, nitrogen and phosphorns. The resnlts obtained are recorded in Table 18. Table 18. -PercipiTaTEd Malivre Noire, Carbon. Nitrogen and Phos- phorus IN Precipitated 3fatihe Noire: Resuets Expressed as Pounds per Two Million Pounds ok Dry Soil (Soil not acid-extracted before treatmen t with ammonia) Number percipitated Matihr Noire Carbon in precipated Dfatiere Noire Nitrogen in precipitated Dfafilre Noire Phosphoru.s in precipitated ISIatilre Noire A B 9174 9203 4262 4303 604 628 20 18 Average 9189 4282 616 19 Phosphorns-nitrogen ratio = i :3J.4 Nitrog'en-carbon ratio =1:7 Phosphorus-carl)on ratio — i :jj5 The results recorded in Tables 17 and iS are very significant as can be more readily seen by glancing at Tal)le 19 which sum- marizes the above data. Tabli: 19.— yi/a///;v' Noire, Carbon, Nitrogen and Phosphorus Precipi- tati';d From Ammoniacal Solution by Hydrochloric Acid: Results Expressed as Percent of Total Soluble in Ammonia. (Soil not acid-extracted before treatment with ammonia) Matiire Noire Carbon Nitrogen Phosphorus 32.7 39.4 37.3 8.0 jpio] Carbon, PiiosnioRus and Nitrogen in Soils 115 Of the total maticrc noire obtained, only 32.7 percent has been precipitated from the alkaline solution by hydrochloric acid. The portion remaining in solution does not consist of inorg-anic salts, as might be supposed, as is readily shown by the fact that only 39.4 percent of the carbon and 37.3 percent of the nitrogen has been precipitated. This shows conclusively that only about 1/3 of the dissolved organic matter has been precipitated. Only 8.0 percent of the total soluble phosphorus, or 19 pounds out of 238 pounds, has been precipitated from alkaline solution by hydrochloric acid. Has the phosphorus remaining in solution in the mother liquor been derived from organic or inorganic sources? The fact that 60.6 percent of the carbon and 62.7 percent of the nitrogen also remain dissolved in the mother liquor would appear to be significant. Having made a study of the maticrc noire obtained from the original soil it seemed desirable to investigate the niatierc noire obtained in the usual way after the soil had been extracted with I percent hydrochloric acid to remove the calcium and magnesium. It seemed reasonable to suppose that the acid extraction would re- move also a considerable quantity, if not all, of the inorg'anic phos- phorus, which may ha\e previously passed into the ammonia so- lution. As before, the amount of luaficrc noire was determined and then extracted in quantity for the determination of carbon, nitrogen and phosphorus. The results obtained will be found in Table 20. Table 20. — Matih-e Noire, Carbon. Nitrogkn and Pho.sphokus in the Mature Noire: Results Expressed as Pounds per Two Million Pounds of Dry Soil (Soil acid extracted before treatment with ammonia) Number 3latiere Noire Carbon in the Matilre Noire Nitrogen in the ilfatihe Ao/;r Phosphorus in the Matiere Noire A B 60840 61660 258(.0 25790 2805 2885 524 508 Averag^e 61250 25825 2845 516 Phosphorus-nitrogen ratio ^ i :5.5 Nitrogen-carbon ratio = i •.9.1 Phosphorus-carbon ratio ^ i 150 The maticrc noire was redissolved in dilute ammonia and an excess of i percent hydrochloric acid added. The amount of the precipitate and the carbon, nitrogen and phosphorus in the precipi- tate were determined as before. The results obtained are recorded in Table 21. 116 Bulletin No. 145 [At HI, Tablk 21. — Pkkcipitatkd Malihc Noire; Cakbon, Nitkoc.kn and Pitospho- Kus IN THE Precipitated Mature Noire: Kesults Expressed as Pounds in Two Mii^lion Pounds of Dry Soil (Soil first acid-extracted before treatment with aminonia) Number Precipitated iMaiilrc N^oire Carbon in precipitated 3/afih'e Noire 11410 11555 Nitro<,''en in precipitated Matihe Noire Phosphorus in precipitated Matihe Noire A B ■ 30110 31140 1242 1198 57 56 Average 30()25 11482 1220 1 56 Phosphorus-nitroo'en ratio = i :2\.y Nitrogen-carbon ratio = i X).'^ Phosphorus-carbon ratio =^ i 1205 'I'ablc 22 summarizes the resuhs reported in Tables 20 and 21. ()f llie total dissolved maticrc noire only 30 percent was precipi- tated. Again the greater part of the carbon and nitrogen remain in the mother li(|uor. Only 44.5 jiercent of the carbon and 42.9 percent of the nitrogen were i)reci[)itated while Init 'S.'j percent of the phosphorus was precipitated. Table 22. — /Matii re Noire; Carbon, Nitrogen and Phosphorus Precipi- tated FKOM AmMONIACAL SOLUTION BV HYDROCHLORIC AciD: RESULTS Expressed as Percent of Total Soluble in Ammonia (Soil first acid-extracted before treatment with ammonia) Matih-e Noire Carbon Nitrogen Phosphorus 50.0 44.5 42 . 9 8.7 Again, the ([tiestion regarding the source of the phosphorus remaining in solution arises. It will be seen that 55.6 percent of the soluble carbon and 58. i percent of the soluble nitrogen also re- main in solution. Attentiou should l)e called to the fact that when the original soil was treated direct with ammonia, withotit previ- ous extraction with h\'(lrochloric acid, under conditions where the UL-Lximum amount of inorganic phosphorus should be dissolved, onl\" 23S ])ounds of phosphorus per tw'o million pounds of soil were obtained: \-et, after the soil had been treated with hydro- chloric acid to remove the calcium, under conditions where the minimum amount of inorganic phosphorus would be dissohed by ammonia, 516 pounds of phosphorus per two million pounds of soil were obtained. The difference between these two numbers, 27S |)ounds, imquestiimably represents phosphorus which must have been derived from organic sources. Now% since only 55 potuids of phosj)horus is precipitated with the maticrc noire by hydrochloric acid, it \vould appear th.'it the organic phosphorus associated with the precipitated inoticrc noire is onlv a A-er\' small i)art of the or- ganic phosjihorus present in the soil. IQIO] Carbon, Phosphorus and Nitrogen in Soils 117 Schmoeger (39) has demonstrated that the organic phos- phorus compounds of the soil are decomposed by heating under pressure. It would appear probable, therefore, that the simple evaporation of the ammoniacal solution on the water bath in the preparation of the niatierc noire in quantity for analysis would cause a decomiwsition of the phosphorus compounds; hence when the niatierc noire is redissolved and precipitated by hydrochloric acid, less phosphorus w^ould be obtained in the precipitate than would be the case if the material had not been heated. This idea was confirmed by experimental evidence as is shown in Table 23. The precipitated matiere noire obtained from the original soil, which had not been extracted with hydrochloric acid, showed 19 pounds of phosphorus per two million pounds of soil. A portion of the ammoniacal extract of this soil was freed from clay by Frap's method; an aliquot part of the extract was then neutralized with hydrochloric acid : the precipitate obtained showed 68 pounds of phosphorus per two million pounds of soil, or over three times as much as did the precipitate obtained from the evaporated ma- terial. Table 23. — Phosphorus in Precipitated Matih-e Noire: Results Ex- pressed AS Pounds per Two Million Pounds of Dry Soii, Soil not acid-extracted Soil acid-extracted Number Phosphorus in heated MatiereNoire Phosphorus in unheated ISIatureNoire Phosphorus in heated Matih-cNoire Phosphorus in unheated MatureNoire Phosphorus in barium precipitate A B 20 18 61 77 56 57 133 164 133 138 Averag-e 19 69 M> 149 135 The acid extracted soil gave similar results : the precipitated matiere noire which had been subjected to heat gave only 55 pounds of phosphorus per two million pounds of soil, while the precipitated matiere noire which had not been subjected to heat gave 149 pounds or nearly three times as much. The latter result was again confirmed. When the ammoniacal extract, freed from clay by precipitation with ammonium sulfate, is treated with barium chloride, the organic matter is quantitatively precipitated as is indicated l)y the decolorizing of the supernatent liquid and by the fact that evaporation of the filtrate and ignition of the residue gives only a veiy faint charring. But unfortunately the barium chloride also precipitates the inorganic phosphorus as barium phosphate under these conditions, and when the liquid is rendered acid it becomes colored, showing that organic matter as well as inorganic phosphorus has been dissolved. However, the precipi- tate was separated by filtration, washed with hydrochloric acid un- 118 Bulletin No. 145 [April, til free from barium and the phosphorus determined. This phos- phorus must have been derived from orj^'anic sources. The resuUs are recorded in the hist cohimn of Table _'3 and compare very well with those previously ol:)tained. According- to Scl'imoe.ger, extraclinu of the soil for 24 hours with 12 percent cold hvdrochloric acid removes all of the inorganic phosphorus readilv soluble in dilute acids. W'tmld not such treat- ment also remo\e an\- in(»rganic phosphorus readil}' soluble in dilute alkali" It would certainly seem that the subschosi)horus determined. Txtth experiments were du])licate(l. The dilute am- monia extracted 540 and ~^jo pounds of i)bos])liorus or an ax'erage of :;:^c^ pounds of pliosphorus per twc^ million pounds of soil which had previouslv l)een extracted with cold ij percent hydrochloric acid, \vhile a second extraction with cr)ld i_> percent hydrochloric acid yielded ouh' (^4 and 96 jiounds or an average of 95 pounds of phosphorus per two million pounds of soil. It would seem reasonable to suppose that both extractions of the soil with cold \2 ])ercent hydrochloric acid removed some organic ])lios])li(ii-us since llerthelot and .\ndre (31) have dennni- strated that organic matter ()\ the soil is somewhat soluble in this reagent. It would also seem \er\- inircusoiialilc to suppose that dilute ammonia ]iossessed as g-reat a solvent power iov inorganic phos- phorus as does 12 percent cold hydrochloric acid. But, assuming, for the sake of argument, that oul\' inorganic phos])horus is ex- tracted l)v the lu'drochloric acid and that dilute ammonia has as great a sohent power for iuorg'anic phos])h()rus as the hydr(")chloric acid, the alxive exi)eriments seem tc) demonstrate that at least 4O0 ])i)unds of ])hosphorus iSSS''^)?'^ "^ ^^^*^ ammonia-soluljle phos- ])horus has been (leri\-e(l from organic sources and that at least J^.^ ]vercenl of tlie ammonia-soluble i)hos])borus has been derived 1 rom organic sources. iQio] Carbon, Phosphorus and Nitrocen in Soils 119 (c) ORGANIC PHOSPHORUS BY SCHMOKGKr'S METHOD The second method for determining- the organic phosphorus is the one proposed hy Schmoeger. Eg'gert, Nilson, Tache and others have shown that simple ignition increased the sohil>ihty of the phosphorus in cold hydrochloric acid. The increased solubility of the phosphorus was believed to be due to the destruction of the org'anic phosphorus compounds. Therefore, the amount of phos- phorus in the original soil, soluble in cold hydrochloric acid, sul>- tracted from the amount in the ignited soil soluble in cold hydrochloric acid of the same strength was reg'arded as having been derived from the organic phosphorus compounds. This as- sumption was confirmed by Schmoeger by hydrolyzing- the soil un- der pressure at a temperature of i40°-i6o°C. This treatment of the soil decomposetl the organic phosphorus compounds so that the organic phosphorus was rendered soluble in cold hydrochloric acid. The difference, therefore, between the amount of phosphorus ex- tracted from the original soil by cold hydrochloric acid and the amount extracted from the soil which had been hydrolized gave the amount of organic phosphorus. Schmoeger found that, as a rule, concordant results were obtained by the two methods altho in cer- tain cases slightly higher results were obtained by the latter method. It was decided to determine the organic phosphorus bv both of the above methods. Thus, lo grams of the orig-inal soil was treated with lOO c.c. of 12 percent hydrochloric acid and digested in the cold with an occasional shaking for 24 hours. A second sample of 10 grams was ignited and then extracted with 12 percent cold hydrochloric acid in a similar manner. .Vt the end of 24 hours the extract was diluted with water and separated by filtration. The residue was washed with cold water until the filtrate was free from chlorides: the filtrate was then made up to 500 c.c. and 100 c.c. used for the phosphorus determination. The results recorded in Table 24 show that there are 271 pounds of phosphorus in the original soil solulile in 12 percent cold hvdrochloric acid while there are 814 poun.ds in the ignited soil solul)le in the same reagent. These results show, therefore, that there are 543 pounds of organic phosphorus in two million pounds of the surface soil. Another sample of 10 grams of the soil was treated with acidu- lated water and heated in an autoclave for 12 hours at a tempera- ture of I40°-I45°C. The sample was then digested for 24 hours with cold hydrochloric acid, filtered and the filtrate made up to 500 c.c. An a\"erage of two determinati()ns show that 878 poimds of phosphorus were obtained. This would indicate that there were 607 pounds of organic i)hos|)horus in two million ])ounds of the surface soil. Sliglul}- higher results for organic phosphorus are thus 120 Bulletin No. 145 [April, obtained Ijy the autoclaA'e method but it is probably more nearly correct since it is difticiilt to conceive how the treatment in the autoclave would render any inorganic phosphorus soluble which would not be rendered soluble l)y io-nition while the work of Leav- itt and LeClerc (81, 82) would indicate that ignition might render some of the organic [)liosi)hurus insoluble in cold hydrochloric acid of any strength. The calculation method shows that 423 pounds of phosphorus per two millions of the surface soil are in organic combination: the ammoniacal extraction method shows 504 pounds of organic phosphorus and the ignition method shows 543 pounds, while T.\BLK 24.— Phosphorus Soluble in Twelve Percent Hydrochloric Acid: Results Expressed as Pounds in Two Million Pounds ok Soil Number Original soil Ignited soil Organic phosphorus A B 26(1 276 819 809 Average 271 814 543 Table 25. — Phosphorus Soluble in Twelve Percent Hydrochloric Acid: RivSULTs Expressed as Pounds in Two Million Pounds oe Soil Number Original soil Evaporated soil Organic phosphorus A B 266 276 876 880 Average 271 878 607 Schmocger's mctliod shows that there are 607 pounds of organic phosphorus. The calculation method is, therefore, very conserva- tive in nature and it can be safely stated that at least that much phosphorus is in organic combination. Tal)le 26 gi\es the sum- marized results of 1I1C organic ])hosphorus ol)tained bv the several methods. Table 26. — Total Phosphorus and Organic Phosphorus by Several Methods Organic phos- phorus by cal- culation Organic phos- phorus by solu- tion in dilute ammonia ( )rganic phos- phorus by ig- nition Organic phos- phorus by evap- oration (Schmoeger) Total l)hos- phorus Pounds per two million pounds of soil Per- cent of total Pounds per two million l)Ounds of soil Per- cent of total Pounds per two million pounds of soil Per- cent of total Pounds per two million pounds of soil Per- cent of total 919 423 46 504 55 543 60 607 66 /p/o] Carbon, PHOsruoRUs and Nitrogen in Soils 121 CONCLUSIONS 1. The phosphorus-nitrogen ratio in the surface soil of tlie brown silt loam soils is i :i3.5 while the same ratio in the black clay loam soils is i :ii.4. 2. Under normal conditions the nitrogen-carbon ratio of the soil has a tendency to become narrower as the age of the organic material increases : the ratio, however, never becomes narrower or even e(|ual to the ratio of the more common proteins contained in the hunnis producing materials. 3. The nitrogen-carbon ratios of the ordinary brown silt loam soils of Illinois are 1:12.1, 1:11.5 and 1:8.9 ^^^ ^^''^ surface, sub- surface, and subsoil respectively. The ratios in the black clay loam soils are i :ti.7, i :ii.9 and I :g in the surface, subsurface, and subsoil respectively. 4. The phosphorus-carbon ratio in the surface soil of the browai silt loam is i : 165.2 while the ratio in the surface soil of the black clay loam soils is i : 163.6. 5. The calculation method for determining organic phosphorus is very conservative in character and can be relied upon in drawing broad general conclusions. 6. The evaporation on the water bath of the ammoniacal so- lution, in the preparation of the iiiaUcre noire in quantity for analy- sis, causes a hydrolysis of the organic phosphorus compounds. 7. The determination of the phosphorus associated with the precipitated maticrc noire is not a quantitative method for the de- termination of the total organic phosphorus of the soil. It should be regarded only as a good qualitative evidence of the existence of organic phosphorus in the soil. 8. The contention of Fraps that, "There is no evidence that the phosphoric acid in the filtrate is in organic combination" and that, "It is probably derived from the iron and aluminium phos- phates" is entirely untenable. iQio] Carbon, Phosphorus and Nitrogen in Soils 123 BIBUOGRArHY 1. MuLDivR, — L\'l)cr (lie liestandtlieile dcr Ackcrcrdc. Journal fiir praktische Chemie : ( i(S44), Band 32, S. 326. 2. Wolff', — Zeitschrift fur Analytische Clieniic : (1864), Band 3, S. loi. 3. 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Record: ( [904), Vol. 16, P- 555- 58. i\so, — Leber das Vorkommen von Phosphorsaure in (^rgan- ischen Verbindungen im Bioden. Biedermanns Central-blatt fiir Agrikulturchemie : (i(;04), Band 34, S. 3. 5(). PiCTTiT and vSciiAL^B, — The Determination of Org"anic Carbon in Soils. Jr. Am. Chem. Soc: ( 1904), Vol. 26, p. 1640. 60. PlAirrVsKiJ, and l\i".i-Uo(u;, — The IMiosphorus associated with the Organic Matter of tlie v^oil. Rhode Island Agr. Exp. Sta. Rept. ( 1904-05 ),. p. 2()H. ()]. CamI'Rox and 1 >ri; \zi:ai,i;, — The Organic Matter in Soils and Sulisoils. jr. Am. Chem. v^oc. : (1(^04), Vol. 2(), p. 29. ()2. Di'MONT, — Sur les engrais ]uimi(|ues complets. Compt. rend.: ( 1904), tome 138, p. I42(^. ()7,. Cameron, — A Comparison of the ( )rganic Matter in Dift'erent Soil Ty])es. Jr. Am. Chem. Soc: ( H)0~,), Vn\. 2~, p. 256. 64. Dr.MoxT, — v^ur la \aleur agricole des matieres humi(iues. Compt. rend.: ( 1905), tome 140, p. 2^. 186. 66. 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Hiegard. — Some Peculiarities of Rock-weathering and Soil Formation in the Arid and Humid Regions. The American Journal of Science: ( 1906), Vol. 21, Series 4, p. 261. 74. Andre, — Sur la constitution des matieres humiques naturelles. Compt. rend.: (1898), tome 127, p. 414. 75. Berth EEOT ET Andre, — Sur les principles azotes de la terre vegetale. Ann. Chim et Phys. : (1887), sixieme serie, tome II, P- 3f>8- 76. Bertheeot et x\ndrk, — Faits pour servir a Thistorie des principles azotes renfermes dans la terre vegetale. i\nn. Chim. et Phys.: (1892), sixieme serie, tome 25, p. 314. yy. MooERS and Hampton, — The Separation of Clay in the Esti- mation of Humus. Jr. Am. Chem. Soc. : (1908), Vol. 30, p. 805. 78. vSl'zU'KI, — Studies on Humus Formation. Chemical Abstracts: ( 1908), Vol. 2, p. 570. 79. Eggertz und NiESON, — Chemishe Untersuchung von Moor und Torfboden. Biedermann Central-l)latt fi_u- Agrikultur- chemie: (1889), Band 18, S. 664. 80. Stoddart, — Soil Acidity in its Relation to Lack of Available Phosphates. The Journal of Industrial and Engineering Chemistry: (1909), Vol. i, p. 71. 81. Leavitt and LeCeERC, — Loss of Phosphoric Acid in .\shing of Cereals. Jr. Am. Chem. Soc: (1909), Vol. 30, p. 391. 82. Leavitt and LeClERC, — Determination of Phosphorus in Ash Analysis. Jr. Am. Chem. Soc: (1908), Vol. 30, p. 617. LIBRftRY OF CONGRESS 002 672 684 -4