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Quantitative Relationships of Carbon,

Phosphorus, and Nitrogen in Soils

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 4PLINOIS

Agricultural Experiment Station

BULLETIN NO. 145

QUANTITATIVE RELATIONSHIPS OF
CARBON, PHOSPHORUS, AND
NITROGEN IN SOILS

By ROBERT STEWART

ED cin oe ir eae ayy GD - <Ee- a

AU

URBANA, ILLINOIS, APRIL, 1910

o~

Nore

Robert Stewart was born in American Fork, Utah, August 16,
1877. He secured his common school education in the public
schools of Utah. In the fall of 1896 he entered the preparatory
department of the Agricultural College of Utah. He graduated
from this institution in June, 1g02, with the degree of Bachelor of
Science. 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
1g05 he was appointed assistant professor of chemistry in the Utah
College and while holding this position, during the years 1905-06,
1900-67, 1907-08, he continued his graduate student work. Dur-
ing the summer of 1906 he was a member of the Graduate School
of Agriculture held at the University of Hlinois. In June, 1998,
he was appointed professor of chemistry in the Utah College and
was granted a leave of absence to carry on graduate work at the
University of Illinois.

He is the senior author of Bulletin 103, “Milling Qualities of
Utah Wheat,” and Bulletin 106, “A Study of the Influence of Irri-
gation Waters upon the Movement and Production of Nitrates in
the Soil,” which has been accepted for publication by the Utah Ex-
periment Station.

During the school year 1go&-cg he held a fellowship in agron-
omy in the University of [linois. He is a member of the Illinois
chapter of Sigma Ni and also a charter member of the Illinois
chapter of the American Society of Agronomy.

QUANTITATIVE RELATIONSHIPS OF
CARBON, PHOSPHORUS AND ~ :-
NITROGEN IN SOITLS*

By ROBERT STEWART

(A) HISTORICAL RESUME

The literature on carbon, nitrogen and phosphorus:in soils is
voluminous. The résumé given herewith by no means attempts to
include all that pertains to these elements in the soil, but it 1s con-
fidently believed that it fairly represents the literature pertaining
to this particular phase of the subject.

I. CARBON IN SOILS

Carbon may exist in soils as inorganic and organic carbon. The
agricultural value of organic carbon, or organic matter, of soils
has long been recognized by the practical husbandman, and the
scientific man early recognized its value when the applications of
science were made to agricultural problems.

Milder (1) in 1844, made an elaborate study of the organic
matter of the soil, and seems to have been the first one to suggest
that it consisted of other elements than carbon, hydrogen and
oxygen. He separated the organic matter into various supposed
pure organic compounds of an acid nature, which were analyzed
and studied by the usual organic method.

Wolff (2) determined the organic matter of the soil by calcu-
lation, by use of the factors 1.724 or 0.471: he multiplied the or-
ganic carbon by the former factor, or the total organic carbon
dioxid by the latter. The factors were derived from the concep-
tion that “humus” contained 58 percent carbon.

Detmer (9) attempted to isolate ‘‘pure’” humic acid from the
soil and to study its properties. Fle obtained a fairly pure product
which he studied and submitted to analysis.

A little later Grandeau (10) developed his well known method
for determining the matiére noire of soils, which he regarded as
of great importance. He stated that soils owed their color and

*Submitted to the Faculty of the Graduate School of the University of Illinois in partial
fulfillment of the requirements for the degree of Doctor of Philosophy, June, 1909.

91

92 BuLieTiIn No. 145 [April,
probably their fertility to its presence since it held in combination,
phosphorus, nitrogen, and certain mineral elements.

Dehérain (22) determined the carbon content of soils from
plots which had received different treatment. He found that the
soils from the plots which had not been manured had lost over
50 percent of their carbon.

Kostytschiff (24) studied the humus obtained from substances
of known origin and which were converted into humus under con-
trolled conditions. He learned that even with the albuminous sub-
stances the carbon was lost more rapidly than the nitrogen, hence
the ratio of carbon to nitrogen would be narrower in the resulting
humus than in the original material.

3erthelot and André (31) found that 67.1 percent of the total
carbon in soils was soluble in dilute alkalis but that over one-half
of this soluble carbon, or 40 percent of the total carbon, was not
precipitated from the alkalin solution by the addition of an acid.

Snyder (37) reported the results obtained by a study of the
production and analysis of the humus obtained from such sub-
stances as cow manure, clover, meat scrap, etc., etc., which were
converted into humus under known conditions. The carbon
content of the humus varied from 41.95 percent in case of the hu-
mus produced from cow manure to 57.84 percent in case of the
humus produced from cane sugar.

Hess (45) studied the effect of different systems of treatment
on the humus of the soil. He found that the ratios of carbon to
nitrogen and nitrogen to humus were not materially effected by the
treatment applied.

André (47) studied the action of potassium hydroxid on the
carbon compounds of the soil, mould, compost and peat. He de-
termined the insoluble and soluble carbon: the latter he separated
into two classes; the portion precipitated from alkalin solution by
the addition of an acid, and the portion remaining in solution. The
results obtained are expressed in Table 1.

TABLE 1.—PERCENTAGE OF SOLUBLE AND INSOLUBLE CARBON AND RATIO
OF CARBON TO NITROGEN

Bow Compost Soil Mould
ald hese isatia oe Ratio fee ase aan
i. C/N mat C/N ae C/N por C/N ait
Insoluble portion |147.6 | 24.5 84.4 4).0 82.4 35.4 40.4 41.8
oie tt beradus @*) 26.9 44.8 | 16.6| 23.0 | 27.1| 36.6 | 10.8| 18.7
Fon Paer ed 17.7 | 30 7 | 9.81 37.0 | 16.7| 28.0 | 10.1 | 39.5

1910 | CARBON, PHOSPHORUS AND NITROGEN IN SOILS 93

The ratio of carbon to nitrogen in the original material was:
peat 22.7; compost 15.0; soil 24.7 and mould 12.8. He concluded
that the more insoluble the compound the wider was the carbon-
nitrogen ratio. The potassium hydroxid showed a tendency to dis-
solve the compounds rich in nitrogen.

Pagnoul (51) found no fixed relation between the carbon and
nitrogen of the soil but apparently the carbon, nitrogen, and humus
varied in the same direction, altho irregularly.

Rimbach (53) concluded that, since the matiére noire was
readily nitrified it was the direct source of the nitrates of the soil
and thus the insoluble carbon was of insignificant value.

Frear and Hess (54) found that lime caused a more rapid loss
of carbon than of nitrogen in manured land, but the reverse in un-
manured land.

Dyer (55) studied the carbon and nitrogen content and the re-
lationship between carbon and nitrogen in the soil taken from 22
different plots of the Rothamsted experiment fields. ‘These data
are furnished for each individual g-inch section to a depth of go
inches.

The carbon and nitrogen contents of the higher depths were
higher than those of the lower depths and the ratio of carbon to
nitrogen is wider in the former. At the fifth to sixth depth the
carbon and nitrogen contents seem to become fixed quantities and
are apparently those derived from the original matter out of which
the soil was formed.

A study of various clays and other material taken from great
depths seemed to indicate that a nitrogen content of .o4 percent
was indigenous to the subsoil of the Rothamsted station.

Cameron and Breazeale (61) investigated the three general
methods for determining the carbon content of the soil: namely,
the “loss on ignition” method, the humus method and two forms
of a combustion method. They concluded that the first two meth-
ods were unreliable: the first, because there was no apparent re-
lationship existing between the results obtained and the true carbon
content; the second, since it makes no pretense of giving the total
carbon in the soil.

It is interesting to note that they reported that the ammoniacal
extract contained so much suspended material that it was found
undesirable to work with, until it was passed through a Chamber-
land-Pasteur filter, when a perfectly clear solution was obtained.

Konig (67) recently studied the influence of hydrogen peroxid
on the organic matter of the soil. He found that it consisted of
two parts, one easily oxidized by hydrogen peroxid, the other not
oxidized by this reagent.

O4 Butierin No. 145 [April,

Hopkins and Pettit (68) reported the total carbon, nitrogen
and phosphorus contents of a great number of samples of the soils
of Illinois. his work is, thus, 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 chiefly as organic nitrogen with a
very small amount of inorganic nitrogen. ‘The organic nitrogen
may exist in some known and probably some unknown forms.

Milder (1) believed the nitrogen, found in the humus, to be
associated with the organic matter in the form of the ammoniacal
salts of the various organic acids obtained by him.

Miller (4) thought he detected a tendency for the nitrogen to
vary inversely as the carbon.

Detmer (9) believed that the nitrogen formed a definite com-
pound with the organic carbon of the soil since the nitrogen could
be liberated only with great difficulty and by the use of the most
drastic chemical agents.

Simon (11) believed that the organic matter of the soil pos-
sessed the property of absorbing the free nitrogen of the at-
mosphere and of converting it into ammonia which in turn united
with the organic acids in the form of their ammoniacal salts. Sos-
tegni (19) a little later discussed the work of Simon and reported
a series of experiments to prove that Simon’s assumption was un-
tenable.

Berthelot (19), in 1886, reported the carbon and nitrogen con-
tents of calcareous clayey soil, originally very deficient in organic
carbon and nitrogen but which was gradually increasing 1n carbon
and nitrogen content owing to the action of diatoms.

Berthelot and André (20, 74, 75, 76) later carried on a series
of experiments for the purpose of separating the organic mitro-
genous material into its various compounds. ‘They reported the
amount of total, nitric, amido and ammoniacal mitrogen present in
the soil.

Eggertz (21) differed very materially from Mulder. He con-
cluded that Mulder’s contention, that the nitrogen associated with
the organic matter of the soil existed only as the ammoniacal salts
of the various organic acids, was untenable. If the nitrogen ex-
isted simply as the ammoniacal salt of the humic acid, treatment
with hydrochloric acid should liberate all the nitrogen as ammonia,
which, experimental evidence showed, was not the case.

Furthermore artificial humic acid, treated with ammonia, did
form ammonium humate which, however, was readily decomposed

r9ro0| Carson, PHospHoRUS AND NITROGEN IN SOILS 95

by treatment with a mineral acid; yet, if this artificial humic acid
be heated in a current of ammonia gas, combination took place and
the resulting compound could not be decomposed by treatment
with mineral acids. He, therefore, concluded that the nitrogen
formed an integral part of the humic acid radical.

Berthelot and André (26) studied artificial humic acid pre-
pared out of sugar. ‘This acid formed salts with various bases,
which were easily decomposed again by treatment with an acid,
except in the case of the ammonium salt, the nitrogen of which
could not be entirely liberated by this treatment. They concluded
that the nitrogen in part at least, formed an integral part of the
humic acid radical.

Hilgard and Jaffa (30), in 1892, propounded their well known
view regarding the importance of the nitrogen associated with the
extracted matiére noire.

Berthelot and André (31) regarded the organic matter of the
soil as of great importance since it prevented the loss of nitrogen
thru drainage since the nitrogen was held in insoluble combination
in the organic matter.

Fulmer (38) determined the humic nitrogen in 53 samples of
Washington soil and attempted to work out the relationship be-
tween carbon and nitrogen by means of the formula c= 7+”,
where c= the percentage of nitrogen in the matiére noire; b=
the percentage of the total soil nitrogen; a= the percentage of
humus. By means of this formula the 53 samples of soil were
separated into three classes; the first class contained 19 samples in
which the variation in the humic nitrogen calculated by means of
the formula was within one percent of the analytical result; the
second class contained ro samples and the variation was from one
to two percent; the third class contained 24 samples and the varia-
tion was anywhere over two percent. ‘These results furnished good
evidence that no one given relation would hold for all soils.

Wheeler (48) found that lime or gypsum caused a decrease in
the amount of humus but that the percentage of humic nitrogen
was increased. Similar results were obtained by 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 black Russian soils. The results are
reported in ‘Table 2.

96 3ULLETIN No. 145 [ April,
TABLE 2.—PERCENTAGE OF Toray, Humic, AMIpo, AMID AND AMMONIACAL
NITROGEN IN HuMus

Percent in dry substance 1 Ss A le a
: of nitrogen
Lota Amido | Amid Ammo- Amido Amid Ammio-
No. humic nitrogen| nitrogen niacal nitrogen) nitrogen niacal
nitrogen 2 = nitrogen = 8 nitrogen
1 2.130 1.34 0.31 0.04 49 09 11.238 1.46
2 3.38 1.81 0.41 0.08 53.55 awe! 3236
3 2.64 1.30 0.29 0.02 49.20 10.99 0.80
4 BI co. 2034 0.32 0.03 TRON 9°61 0.90
5 4.58 aROpk 0.48 0.06 22.01 10.46 1531
6 aed OS, 126 0)27 0.07 34.52 7.40 1.90
7 4.02 1.96 0.22 0.03 48.75 | 5.47 0.78 —
This did not account for all of the nitrogen present and so the

question arises in what form does the remainder exist?

D’Utra (70) found that the humic nitrogen showed wide vari-
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 be 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, 1s 0.101 percent and 0.101 per-
cent respectively, while the total nitrogen of the ordinary brown
silt loam soils of the corn belt in Hlinois varies from 0.218 percent
to 0.337 percent.

3. PHOSPHORUS IN SOILS

The phosphorus of the soil may 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.

Mulder (1), as early as 1844, noted that the organic material
was not readily freed from phosphorus.

The work of Thénard, Schutzenber (5, 6, 7) showed that union
may take place between various forms of artificial humus and phos-
phates 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

1910] Carson, PHospHorus AND NITROGEN IN SOILS 97
that the material could be freed from phosphorus only with great
difficulty.

Grandeau (10) regarded the phosphorus associated with the
extracted matiére noire as being of the greatest importance, and,
was probably in special combination with the organic matter. Tle
regarded it as an index of the fertility of the soil.

Simon (11) believed that he had demonstrated that union 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 ability of the soil for phosphates.

Kichhorn (13) repeated some of Simon’s work and concluded
that organic combination did not take place as indicated by Simon
but that the humus had decomposed the tri-calcium phosphate with
the formation of acid phosphate.

Pitsch (14) determined the solubility of the various mineral
phosphates, including iron and aluminium phosphates, in a solu-
tion of ammonium humate itself. He concluded, that, since this
solution exerted a solvent action on mineral phosphates, the am-
mona extract of the soil contained phosphorus, other than that
originally associated with the organic matter in the soil and prob-
ably part, at least, of the ammonia soluble phosphorus was derived
from the iron and aluminium phosphates.

M. P. DeGasparin (15) found in calcareous clay 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 the 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.

Fggertz (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 was 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 yield up its
phosphorus to acids.

93 BULLETIN No, 145 [April,

Tan Bemmelen (23) believed that the iron, calcium, silica,
phosphoric acid, etc., found in the ash of the matiére noire by Eg-
vertz, were not originally chemically combined to carbon in the
organic matter of the soil but were absorbed by the precipitated
eelatinous maliére noire. According to Van Bemmelen the phos-
phorus existed in the soil principally as calcium phosphate with a
very small quantity occurring in the absorbed state in the form of
a colloidalen Humate-Silicat-K omplex.

‘Two questions seemed to be of paramount importance to Wik-
lund (25) regarding the work of Nggertz: first, was the amount
of the ammonia-soluble phosphorus obtained from different soils
constant? Second, did the phosphorus exist in the mullkorpers
(matiére noire of Grandeau) in chemical combination with carbon,
or simply as absorbed phosphorus? He concluded that there was
a tendency for the ammonia-soluble phosphorus to be constant in
different soils. He showed, further, that one digestion with 12
percent hydrochloric acid did not completely remove all of the
acid soluble phosphorus, but a second and even a third digestion
still removed some phosphorus. Now, he reasoned, 1f the phos-
phorus removed by the second and third digestion was simply ex-
tracted from the absorbed phosphorus, extraction of the soil with
ammonia after the first digestion with hydrochloric acid, should
yield a solution of matiére noire containing a higher phosphorus
content than when the soil was completely extracted with the hy-
drochloric acid. Such, however, was not the case, therefore, the
phosphorus did not exist as absorbed phosphorus and must be in
combination with carbon in the organic matter.

Snyder (34) noted that some phosphorus, iron, etc., were ex-
tracted with the matiére noire but he did not seem to think at this
time that there was any evidence of combination with carbon.
About the same time he observed the rapid loss of phosphorus as-
sociated with the humus in continuous cultivated soil,

According to Berthelot and André (27) phosphorus may be
found in the soil (a) in inorganic or mineral phosphates, (b) in
organic ethers and (c¢) in organic or mineral compounds not read-
ily decomposed.

Schmoeger (29) reviewed 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-
phorus of peaty soil more readily soluble in acids.

It seemed possible to Schmoeger that the soil might possess
such a tenacious absorbent power for phosphorus that it would not
yield up its phosphorus to acid treatment before ignition, But he
deduced experimental evidence to show that such was not the case.

1910 | CarBpon, PHospHORUS AND NITROGEN IN SOILS 99

Digestion of the soil itself and also the extracted matiére noire
with a solution of potassium hydrogen phosphate failed to add any
phosphorus which was not again recovered by treatment with
hydrochloric acid. ‘This was conclusive evidence to Schmoeger
that the phosphorus did not exist as absorbed phosphorus and must,
therefore, exist in organic combination. ‘Two possibilities sug-
gested themselves to Schmoeger: first, the phosphorus existed in
fhe 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 150-160 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) confirmed his previous work and _ pro-
duced additional evidence in favor of his view that nuclein or simi-
lar bodies existed in the soil. Table 3 shows some of the results
obtained.

TABLE 3.—PERCENTAGE OF SULFURIC ACID AND PHOSPHORUS SOLUBLE IN
DILUTE AcID

Percent

Sulfuric Acid | Phosphorus

SotlanonicinalsState sc .ceue acces = 5 sles, wsib ja susser sus 0.122 0.043
Evia Onde GesOrl erty auc, 6 sclorey atetiere alee ais af eeusteie.s * 0 290 0.083
Mite SGM er ea a nesta cecthtes. penis ebesen cs: c8 0.939 0.095

Since sulfur is regarded by 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 regarded as evidence in favor of lis 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. ‘This was regarded as additional evidence 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
combination which was destroyed by the process nes 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 Fie to substances of
a strong acid nature which acted upon the insoluble phosphorus
compounds rendering the phosphorus soluble.

100 BuLietin 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 70-80" rendered over 50 percent of the total phosphorus
soluble in water.

Snyder (36) reported 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 matiére 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 phosphorus. He found that 0.057 percent of phos-
phorus was extracted with the matiére noire. When the ammonia-
cal solution of the matiére 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 believed that he detected the presence of lecithin
and chlorophyllan.

Ladd (43) found in a study of eight samples of different soil
that an average of 41 percent of the phosphorus was associated
with the extracted matiére 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 matiére
noire also increased. From the fact that the organic precipitate,
formed 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 P2Os5 in the ash of the
matiére 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
phosphorus. He attributed this action to the destruction of the
humophosphates.

1910 | CARBON, PHospHORUS AND NITROGEN IN SOILS 101

Aso (58) confirmed, in a general way, the results 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.

oe Ignition rendered the phosphorus in organic combination
available.

Hartwell and Kellogg (60) found that an average 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
which was as follows: soluble matter (in dilute alkali) 50.4 per-
cent; insoluble matter 49.6 percent; total nitrogen 1.6 percent;
total phosphorus 1.27 percent.

The soluble portion contained 35 percent of the nitrogen and
46 percent of the phosphorus. In order to obtain data upon the
state of combination of the phosphorus, the ammoniacal solution
of matiére noire was treated with various reagents with-the result
(recalculated to the element basis) shown in mT: able 4.

TABLE 4.—DISTRIBUTION OF PHOSPHORUS WHEN MATIERE NOIRE IS

PRECIPITATED
aS y 7 miciiona. . *
Precipitating agent
In precipitate} In filtrate

(Cee). Voli (Ane er ORE otc Meee ean aa arr ae 0.383 0 203
liv. TOGHIOLIC ACIC wie «sie viel + eictois 1,0 orsisiere ts ese ‘2 0.386 0.199
Menciceschlorid:-.<2-<.<..- Sa A uctcne hectare: fe aces wisn Shelter aie ater 0.532 0.053
Aduniinium stlfates.. o..% « «6c. Spe forme noe 0.566 0.019
Walon MCOLORIG. .a.ste gers ss ae ais oe her paetes Mee 0.534 0.0009

These results furnished conclusive proof to Dumont 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 decaying 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 obtained by precipitating
the matiére noire in the presence of potassium hydrogen phosphate
by different reagents as indicated in Table 5.

102 Bu.ietin No, 145 [April,

TABLE 5.—AMOUNT OF PHOSPHORUS IN PRECIPITATED HUMUS AND FILTRATE

Series A Series B Series C

Phosphorus in- Phosphorus in- Phosphorus in-
trodiced=.087 troduced= .218 troduced=.437
1 ee Phos- Phos- Phos- Phos- Phos- Phos-
Precipitating phorus | phorus | phorus | phorus | phorus | phorus

agent in in in in in in
humus | filtrate | humus | filtrate humus | filtrate
ACETIC ACIG, ciamce 4 0.056 0.031 0.057 0.160 0.058 0.374
Citricratidies +. co. 0.054 0.033 0.055 0.163 0.054 0.381
Hydrochloric acid} 0.057 0.030 0.059 0.158 0.059 0.378
veiled iaahes Cor Mea (ale, 0.057 0.030 0.061 0.156 0.062 0.372

Altho the amount of dipotassium phosphate added to the
solution had increased, the amount of phosphorus absorbed by the
humus was practically constant, due to the formation of definite
“composes phospho-humique.”

Konig (67) found that hydrogen peroxid oxidized from 40
percent to 70 percent of the humus present in the soil and that
much more of the phosphorus was soluble in pure and carbonated
water after 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. He confirmed Pitsch’s results regarding the
possibility of some of the ammonia-soluble phosphorus being of
inorganic origin. He separates the 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 solution was neutralized with an acid.

3. The phosphorus which remained in solution after the pre-
cipitation of the organic matter.

With the soils under consideration he found that 1/9 of
the ammonia-soluble phosphorus was in the first class, 1/3 was in
the second class and 5/9 was in the third class.

The phosphorus found in the first class was assumed to be as-
sociated with the 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 (77) recently proposed a method for
obviating the error introduced in the humus determinations by the

1910] CARBON, PHOSPHORUS AND NITROGEN IN SOILS 103

suspended clay. They claimed that filtration through the Cham-
berlain-Pasteur filter, 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 dryness 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 uniform potassium
content of the surface, subsurface, and subsoil and by the fact that
different 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 difference 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 the total amount of organic
phosphorus present in the surface soil could be calculated.

4. CARBON AND NITROGEN CONTEN’T OF FUNDAMENTAL ROCKS

The fundamental rocks out of which soils have been formed
contain an appreciable 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 nitrogen was indigenous to the underlying
soil material.

r910| CARBON, PHOSPHORUS AND NITROGEN IN SOILS 105

(B) EXPERIMENTAL PART

The starting point of such an investigation consists of a con-
sideration from a mathematical point of view of the existing data
regarding the relationships of carbon, phosphorus and nitrogen of
the soil.

1. MATHEMATICAL,
(a) INFLUENCE OF AGE UPON THE NITROGEN-CARBON RATIO

From the data available in the literature it is possible to deter-
mine within certain limits the influence 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 from 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
found in Table 6. ‘The materials naturally fall into two groups:
in the first group the ratio varies from 1:52.2 for corn stover to
1:84.1 for wheat straw; in the second group the variation is from
1:16.7 for alfalfa hay to 1:35.4 for timothy hay.

TABLE 6.—APPROXIMATE NITROGEN-CARBON RATIO IN THE MORE COMMON
HuMvuS PRODUCING MATERIALS

Carbon tol

Kind of material sae
of nitrogen

GOMES TOV.Cl cis cic csterea sus ase el levee 4 @ oe O272
Oatestiraw :2 racine 2 oeiiae Mamet sas Seal) Gvae
Wheat straw....... ie eieteistcue eave eee |) tL:
Tea OLMiy WalVisersie ssies << Beno entice ate ep 35.4
CIOVEritAy = crstes te +9 ae cr sip eters Ae 21.3
COW Mea Mayers ores c core pitiless eat Pets 5.035 1955
Alfalfa hayye.cc. +2 Hs wis scopes ere Oe as 16.7
AAT DUMN sass. Ena ORSON NE EE teeth ete 32
DAE Caley enc ee RS Oe TEC 3.4
INO bid Kepler pe ten aio tise CI e 2.8

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 1:2.

The next step in the study in the influence of age upon the
nitrogen-carbon ratio would be to determine the ratio in as fresh
humus as possible from known materials. Snyder (35) in his
study of the production of humus from known materials placed a
weighed quantity of the material together with a weighed quantity

106 BuLietin No. 145 [April,

of soil having a low humus content in a box and set aside for one
year. At the end of the experiment the humus was extracted and
the carbon and nitrogen determined in the matiére 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 is evidently not a quantity which can be ignored since
the humus content of the original soil is .06 percent while the total
nitrogen of the soil is .o2 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
humic nitrogen would more probably 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

TABLE 7.—MINNESOTA SoIL STUDIES: Humus PropucrioNn From KNowNn

MATERIALS
Percent Ratiode
Material used H ; Carbon Nitrogen (carbon to 1
peas in humus | in humus [of nitrogen
Cyripcirvall SOil pas se was 4s ar 0.06 if ? ?
COW? Wd UPe oe saenaye oe ore 0.58 41.95 6.16 6.8
GIOVE Pick su eeie ys cones Ln 0.37 54.22 8.24 6.0
MGAt SOTADS, J cance. dagaees 0.31 48.77 10.96 4.5
COAt Stba tas ut cus Fasteu 0.46 54.30 2250 2152
PijUt @s.¢- Fis oe tee ee 0.47 51.02 5.02 10.2
DAW CUS, vias a ewes eaten Os 49 28 0.32 153:8
SoH PAT wg WES Re Vid ee ale 0.32 57.84 0.08 741.0

the first five substances the variation is from 1:21.7 for oat straw
to 1:4.5 for meat scraps.

The large number of carbon and nitrogen determinations made
in the soils of Hlinois (68) rendered it possible to determine the
nitrogen-carbon ratio, not only for the surface soil, but also for
the subsurface and subsoil. ‘The average of 1g determinations for
the soil type, gray silt loam on tight clay, gave the ratios 1:10.4,
1:8.8, and 1:7.6 for the surface, subsurface, and subsoil re-
spectively. ‘The ordinary brown silt loam soils as an average of
68 determinations gave a mitrogen-carbon ratio of 1:12.1, 1:11.5
and 1:8.9 for the surface, subsurface, and subsoil respectively. The
black clay loam soils as an average of 25 determinations gave
I:11.7, 1:11.9 and 1:9 respectively in the surface, subsurface, and
subsoil. ‘The peat soil as the average result of 5 determinations
gave 1:11.8 and 1:12.9 for the surface and subsoil respectively.

1910] Carson, PHospHorus AND NITROGEN IN SoIts 107

TABLE 8 RATIOS OF CARBON AND NITROGEN IN ILLINOIS Sorts

Soil Reece Carbon to 1 of nitrogen
type Soil types which
No. calculations| Surface Sub- Subsoil
are based surface
Gray silt loam on
330 EUS LG CLAN Giese or0xe « 19 10.4 8.8 7.6
426 |Brown silt loam..... ial a ARES a ale 9.6
526 |Brown silt loam..... 8 13.2 12.9 8.7
626 |Brown siltloam..... 6 11.4 1055 8.7
726 |Brown silt loam..... 4 19 alate al 8.8
1126 |Brown silt loam..... 30 LES) 11.5 8.6
1026 |Brown silt loam..... 9 12.0 1.5 9.3
Averages 68 121 ders 8.9
420 |Black clay loam..... 7 1252 127.2 8.9
520 |Black clay loam..... 5 124 12.2 11.4
1120 |Black clay loam..... alal Meal ale Leal 8.3
1220 |Black clay loam.... 2, 5 by ee? 12.2 7.4
Averages 25 ob Ley 11-9 20
ISO Weep mpeaty ccc cice ot 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
go inches. These results will be found in Tables 9 and 10. The
ratio for the Broadbalk wheat fields varies from 1:9.5 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 1:10.6 to 1:8.8 for the surface and sub-
soil respectively.

TABLE 9.—BROADBALK WHEAT SOILS: RATIO OF CARBON TO NITROGEN

Percent Cn ;

7 aii ar ar arbon to 1

oe di Carbon eats of nitrogen
Hirst Qinches (alliplaits).<. 02. .s02-<-..: 1.155 | 1222 9.5
SecomdsQumChHesr «cet ese a: Meise fats Seis .640 0784 8.2
Bae OerTl ClESis cate,ccote,- vs eis) el avejous: oslo ee oa 0: .492 0666 7 4
MO Lischy 9 TGHES) ct. 2 cee aeeu pae se 1. vas ae | 339 | .0511 6.6
rR GAO ING IT eS avec am auerecisleats sitcters) sa 045k ane" 279 .0472 5.9
UTES TN ChE Seapets aycteisete Selec aisie ere + os sles .256 .0430 5.9
SEvetthe T11CHESs warelersiaccrv. saw vi eleisucatels 6% .248 .0420 5.9
yA ale TE OTT GILES cicysrele vers (ora folie wis oe bevescrete 215 .0396 5.4
ING TAGE OPTIC HE Sia ane le sie otis owheiead nes als Seu .189 £0391 48
Ment OM ChHESan ; acacia saute sees” uw tieus .188 .0375 5.0

TABLE 10..—HOOSFIELD BARLEY SOILS: RATIO OF CARBON To NITROGEN
: 7 Carbon to 1

ak ee of nitrogen
Hits tint GUESS o%, cam ous ooo ile te sce cree 10.6
SECOMmdsO TNGHES as eile estes oe cac cee 8.8

108 Butretin No. 145 [ April,

Hall and Miller (66) reported the carbon and nitrogen con-
tent, and ratio of carbon to nitrogen in samples of various ma-
terials taken from such great depths as to preclude all possibility
of weathering. Since the nitrogen was always found to be associ-
ated with carbon it was regarded as being of organic origin and
as being derived in part from the organic matter present in the
clay at the time of its deposit. These results are shown in Table 11.

TABLE 11._-CARBON AND NITROGEN IN UNWEATHERED ROCKS

= ; eee at Percent ean
o. of F WICKS a i=l pa soe nek

ail Formation ple was ta oe Nikcoed Ratio

1 |Lower Bagshot Sand, Weybridge..| 18—20 | 0.02 .00384 | 5.4

2 |Upper Greensand, Farnham, Surrey 30 0.032 .00718 | 4.5

3 |Folkestone Beds, Brabourne, Kent. 20 G 019 00453 4.2

4 |Lower Greensand, Sevenoaks...... 3 | 0.076 .OO881 8.7

5 \Wondon. Clay, Londonccic ccaseres8 1302) 0397 OF 95

6 |Gault.Clay, Nackholt, Kent.......-.. 18 | 0427 .0415 | 10.3

7 |Weald Clay, Pluckley. Kent..... i 80° i" O185 .0647 2.0

8 |Caiboniferous Shale, Barnsley....| 1236 1.938 s18/ 14.1

o Lower Gault, Dover, i. ..cs-6c0e <0 280—400) 0.172 10325 bse

10° (Oxford (Clay, DOVern cise. e613 ee vw 920 0.548 .0528 | 10.4

11 |Kimmeridge Clay, Welton Lincs... 246 | 2,139 LOT 20.0

12 |Kimmeridge Clay, Dover ......... 570 0.387 .0455 8.5

13. |Lower Lias, Micketon, Glos....... 700 1.120 0803 13.9

14 |Clay with Flints, Harpenden ..... 10 0577 .0294 | 19.6

NOTES

1. A grey coarse sand.

2. Pale grey fine sandy rock.

3. Coarse yellowish sand.

4. Fine yellowish sand.

5. Solid grey clay.

6. Solid dark green clay.

7. Close grey andred mottled clay.

8. Hard grey 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 above tables that under
normal conditions the nitrogen-carbon ratio of the soil has a tend-
ency to become narrower as the age of the organic material in-
creases. ‘The ratio, however, never becomes narrower or ever
equal to the ratio of the more common proteins contained in the
humus producing materials.

(b) CARBON, NITROGEN AND PHOSPHROUS IN ILLINOIS SOILS

Before discussing the phosphorus-carbon and phosphorus-
nitrogen ratios in the soil it seemed desirable to determine as closely
as possible these ratios in fresh material out of which humus might
be formed.

1910| Carson, PuHospHorus AND NITROGEN IN SOILS 109

TABLE 12._-APPROXIMATE CARBON-PHOSPHORUS AND NITROGEN-PHOSPHORUS
RATIOS IN THE MORE COMMON HUMUS PRODUCING MATERIALS

Carbon to 1|Nitrogen to
Kind of material of phospho-| 1 of phos-
rus. phorus
COnmIStONED. <7 owas «sae e 417 8.0
OatStCaw sissies so joa bee's 420 2
Wheatstraw........ ...++ 525 6.2
Maro tility: Waly.) sy... ee sieves so 283 8.0
Clover hay..... mse ietecee 171 8.0
Wow pealaiyy ae hescec cs vere 181 973
PA fail Paelia ye ace acuciereie cec-arese 186 als
INTIGI Eni 2. 225 <'. eng, Yee She 1.4

The ratios in the more common humus producing materials
calculated from the average of a number of analysis for nitrogen
and phosphorus (68), will be found in ‘Table 12. In the coarser
material the phosphorus-carbon ratio varies from 1:417 to 1:525:
the phosphorus-nitrogen ratio is more constant being 1 :6.2 and 1:8.
In the hays, the phosphorus-carbon ratio varies from 1:186 to 1 :283
while again the phosphorus-nitrogen ratio is more constant, the
variation being 1:11.1 to 1:8. In nuclein the ratios are 1:3.7 and
I:1.4. respectively.

In Table 13 will be found the phosphorus-carbon and phos-
phorus-nitrogen 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.
3oth ratios, it will be observed, are very narrow.

In Table 14 will be found the phosphorus-carbon and phos-
phorus-nitrogen ratios in Illinois soils calculated from the data re-
ported by Hopkins and Pettit (08). The average of 7 calculations
of the gray silt loam on tight clay gave the phosphorus-carbon and
phosphorus-nitrogen ratios as 1:42.6 and 1:13.8 respectively.

TABLE 13.—MINNESOTA SOIL, STUDIES: CARBON-PHOSPHORUS AND NITROGEN-
PHOSPHORUS RATIOS

Carbon to 1\Nitrogen to

Kind of material of phospho- 1 of phos-
rus. | phorus
OTTO Al SO Meas elec s1< vie ? | de
Cow imanttre.e. o-.c. ss: ots) 1
Clover....; . RO Ory ao roe. Tie ata
INT@dtS Cha pSin,.scmiineeiess + OC | 2.2
Oatistrawicgesest verre. ne 38.2 lis)
PO Litany cite see rays Mclereetes Ses 221.0 232
NAN CUIS tga ctr) steis <1) 6 cio 37.0 0.24
NOT OFAN Rt ea -ct, aeleteve olsbensaie alsa 42.4 | 0.06

110 BULLETIN No. 145 [April,

TABLE 14.—ILLINOIS SOILS: ORGANIC PHOSPHORUS; RATIOS OF CARBON TO
PHOSPHORUS, NITROGEN TO PHOSPHORUS AND CARBON TO NITROGEN,
Facrors FOR CALCULATING THE ORGANIC PHOSPHORUS.

Ratios of Factors for
Number of an-/Organic phos-|- calculating the
Soil jalysison which|phorus as per-),, : organic phos-

type | calculations |cent of total eee pe Se phorus trom
: : q o DS 1

No. are based phosphorus phosphorus | phosphorus ee
<r ae 24.4 142, 13.8 0.007012
426 9 34.4 132. 10.6 0.007570
526 8 29.5 185. 14.0 0.005393
626 5 ILS ye, 298. 25.01 0.003348
726 4 38.1 1333 10.5 0.007491
1126 24 40.9 116. 9.9 0.008583
1026 oe : 44.9 125, 10.9 0.007988
ANGEGRE, “59 «| 33.5 165. 13.5 0.006053
420) A 36.0 134. 10.3 0.007441
520 5 poe 2600. 12.0 0.003836
1120 11 46.2 90. 8.3 0.005907
1220 2 32.4 169. 15.2 0.002956
Average 25 a7 4 163. 11.4 0.006113
1401 4 100.0 230. 19.6 0.004311
1401 | (b) 5 100.0 338. 26.5 0.002956

(b) Subsoil (7”—40")

The ordinary brown silt loam soils, as an average of 59 deter-
minations, gave the ratios of 1:165.2 and 1:13.5 respectively. The
black clay loam soils, as an average of 25 calculations, gave the
ratios of 1:163 and 1:11.4 respectively. The ratios in the surface
peaty soil, assuming all the phosphorus to be in the organic state,
are 1:230 and 1:19.6. The ratios in the subsoil of the peaty soil
are somewhat wider, being 1:338 and 1:26.5 respectively.

(c) FACTORS FOR CALCULATING ORGANIC PHOSPHORUS

By means of the carbon-phosphorus ratios established as in-
dicated above, it is possible to develop factors for calculating the
amount of the organic phosphorus in the surface soil from the
total organic carbon. For example the carbon-phosphorus ratio,
1:163, 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 0.006113 parts of organic phosphorus.
Hence by multiplying the amount of organic carbon by the latter
number the amount of organic phosphorus may be 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 number 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.

19r0] CARBON, PHOSPHORUS AND NITROGEN IN SOILS 111

© It will be observed that from 1/4 to 2/5 of the total phos-
phorus of the several soil types considered is in organic combina-
tion. These results indicate that a larger amount of phosphorus
is in organic combination than the work of some American inves-
tigators would lead us to believe.

2, CHEMICAL,

(a) ANALYTICAL, RESULTS OF SOI{, FROM ILLINOIS SOUTH EXPERI-
MENTAL FARM

A sample of soil for a study of the organic phosphorus, by the
available methods for the determination of the organic phosphorus
of the soil, was obtained from the [Hlinois 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 by 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 organic 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.

TABLE 15,—ANALYTICAL RESULTS OF SOIL FROM ILLINOIS SOUTH EXPERI-
MENTAL FARM: RESULTS EXPRESSED AS POUNDS IN Two MILLION
POUNDS OF Dry SOIL,

: Soil - 4 : Phos-
Soil No. ata Potassium Carbon Nitrogen phorus*
1A Surface 36280 41800 3760 938
1B Surface 37120 42180 3844 901
Average Surface 36700 41.90 3802 919%
3A Subsoil 36600 es 1735 702
3B Subsoil B(Sa0 al Mee es 1680 670
Average Subsoil SOKO we Vile cessievecers 1708 686

*Later inspection of the 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
drainage; and a composite sample was subsequently collected at points a short distance from
the tile drain which showed 985 pounds of phosphorus instead of 919 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 46 percent to 43 percent.—C. G. Hopkins.

112

TABLE 16.—-ORGANIC PHOSPHORUS:

BULLETIN No. 145

[April,

RATIOS OF CARBON TO ORGANIC PHOS-

PHORUS, NITROGEN TO 1 ORGANIC PHOSPHORUS, CARBON TO NITROGEN

IN SURFACE SOIL

Pounds of

‘ : F F Factor for
organic Organic Ratios of lewiaes
hosphorus |phosphorus NN ae
: in two as percent the organic
at Nitrogen Carbon to | phosphorus
ae f heslctyicarr to 1 organic ea ies lorganic | from organic
ae soil, Of | PHOSPHOTUS! phosphorus 5 phosphorus carbon
423 40.0 © 9.0 ih 1-2 0.01008
( b) PHOSPHORUS ASSOCIATED WITH THE MATIERE NOIRIS

the two available methods

Ot for determining the organic
phosphorus, the one, the determination of the phosphorus associ-
ated with the matiére noire extracted from the soil by 4 percent
ammonia, has given rise to some confusion. Grandeau (10) re-
earded the phosphorus extracted with the matiére noire as being
probably in organic combination. Eggertz (21), Nilson (79),
Wiklund (25), Dumont (65), Ladd (43) and Snyder (41) also
regarded it as organic in form. Pitsch (14) and Van Bemmelen
(23) took the opposite view. Pitsch thought that part of the ex-
tracted phosphorus may have been derived from the inorganic
phosphates of the soil. Van Bemmelen regarded the phosphorus
precipitated with the matiére noire as absorbed phosphorus. Quite
recently, Fraps (69) concluded that only 1/3 of the phosphorus ex-
tracted by ammonia was in organic combination, while still later
Stoddart (80) concluded that only 1/5 of the extracted phosphorus
was in organic combination. As a result of this conflicting evi-
dence there is considerable confusion regarding the nature of the
phosphorus extracted by ammonia. One cause of this confusion,
no doubt, is the difficulty of getting rig of the suspended clay,—
ordinary filtration will not remove it. Obviously all of the phos-
phorus associated with the suspended clay should not be included
with the organic phosphorus, altho part of it may be organic in
form. Fraps removed the clay by precipitation with ammonium
sulfate. 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 showed that complete
saturation of the ammoniacal extract of the soil with ammonium
sulfate, after the removal of the suspended clay, produced a heavier
qualitative precipitate of organic matter than did the addition of
hydrochloric acid. It would seem, therefore, that the evaporation
method of Hampton and Mooers (77) is more desirable for the

1910] CARBON, PHOSPHORUS AND NITROGEN IN SOILS 113

removal of the suspended clay. Unless otherwise stated the latter
method was used for the removal of the suspended clay in all the
work reported in this paper.

Owing to the conflicting evidence regarding the phosphorus as-
sociated with the extracted matiére noire, it seemed desirable to do
some work with this material other than the simple determination
of the phosphorus.

The soil, without previous treatment with hydrochloric acid to
remove the calcium, was extracted with 4 percent ammonia in the
ratio of 1 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 matiére 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 removed by treatment with a min-
eral acid as in the usual humus determinations.

The suspended clay removed by evaporation was analyzed for
carbon and phosphorus with results as follows: Carbon 3.73 per-
cent and 3.61 percent, or an average of 3.67 per cent; phosphorus
0.118 percent and 0.109 percent, or an average of 0.113 percent.
Since the carbon in the original soil was only 2.09 percent while
the phosphorus was .046 percent, the relative increase of carbon
and phosphorus in the suspended clay indicates undoubtedly 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 convert the organic matter into an im-
palpable powder which would have a tendency to remain sus-
pended in the liquid together with the fine clay particles when the
soil was extracted with ammonia.

The amount of the extracted matiére noire was determined.
It was then analyzed for carbon, nitrogen, and phosphorus. ‘The
carbon was determined by 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-
termined by igniting a sample of the matiére noire and treating
the ash with aqua regia; the silica was removed by evaporation
and the phosphorus determined by the usual volumetric method. A
confirmatory test made by determining phosphorus by fusion with
sodium peroxid gave 0.835 percent and o.815 percent phosphorus
in the matiére noire while the method adopted gave 0.860 percent
and 0.830 percent.

The results obtained expressed as pounds per two million
pounds of soil are recorded in Table 17.

114 BuLietin No. 145 [ April,

TaspLE 17.—Matiere Notre, CARBON, NITROGEN AND PHOSPHORUS IN THE
MATIERE NorrE; RESULTS EXPRESSED AS POUNDS PER TWO
MILLION Pounpbs oF Dry SOIL.

(Soil not acid-extracted before treatment with ammonia)

Nitrogen in | Phosphorus

Number Matiére Noire \Carbon in the the in the
Maticre Noire|Matitre Notre|Matitre Notre
A 27600 10870 1642 233
B 286000 10850 1662 242
Average 28100 10860 1652 238

Phosphorus-nitrogen ratio = 1 :6.9
Nitrogen-carbon ratio = 1:6.6
Phosphorus-carbon ratio = 1:45.60.

The matiére noire was now redissolved in dilute ammonia, an
excess of 1 percent hydrochloric acid added and set aside over
night. The precipitate of organic matter was brought on to a filter
paper, which had previously been dried at 11r0'C and weighed.
‘The precipitate was washed with 1 percent hydrochloric acid, dried
at 110°C and weighed. ‘The precipitated matiére noire was obtained
in quantity and analyzed for carbon, nitrogen and phosphorus. The
results obtained are recorded in ‘Table 18.

TaspLE 18._-PERCIPITATED JMatiére Noire, CARBON, NITROGEN AND PHOS-
PHORUS IN PRECIPITATED Jatiére Notre: ResuLTS EXPRESSED AS
Pounbs PER Two MIr.10N PouNbDs OF DRY SOIL

(Soil not acid-extracted before treatment with ammonia)

sareioniked Carbon in Nitrogen in |Phosphorus in
Number P Syhs een precipated precipitated | precipitated
diy Matiere Notre | Matiire Noire | Matitre Notre
A 9174 4262 604 20
B 9203 4303 628 18
Average 9189 4282 616 19

Phosphorus-nitrogen ratio —
Nitrogen-carbon ratio = 1:7
Phosphorus-carbon ratio = 1 :225

The results recorded in Tables 17 and 18 are very significant
as can be more readily seen by glancing at ‘Table 19 which sum-
marizes the above data.

TABLE 19.—Matitre Notre, CARBON, NITROGEN AND PHOSPHORUS PRECIPI-
TATED FrRoM AMMONIACAL SOLUTION BY HyDROCHLORIC ACID: RESULTS
EXPRESSED AS PERCENT OF TOTAL SOLUBLE IN AMMONIA,

(Soil not acid-extracted before treatment with ammonia)

Matitre Notre | Carbon | Nitrogen | Phosphorus
33.7 | 39.4 Bro 8.0

r9ro]} CARBON, PHOSPHORUS AND NITROGEN IN SOILS 115

Of the total matiére 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 inorganic 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 matiére noire obtained from the
original soil it seemed desirable to investigate the matiére 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 inorganic phos-
phorus, which may have previously passed into the ammonia so-
lution.

As before, the amount of matiére 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.—Matiére Notre, CARBON, NITROGEN AND PHOSPHORUS IN THE
Matitre Noire: RESULTS EXPRESSED AS PouNDS PER ‘wo
MILLION PounDs oF Dry SOII,

(Soil acid extracted before treatment with ammonia)

| | Nitrogen in Phosphorus

Number Mattére Joire Carbon in the the in the
; Matiere Noire Matiere Notre Matiere Noire
A 60840 25860 2805 524
B 61660 | 25790 2885 508 7
Average 61250 | 25825 2845 516

Phosphorus-nitrogen ratio = 1:5.5
Nitrogen-carbon ratio = 1:9.1
Phosphorus-carbon ratio = 1:50

The matiére noire was redissolved in dilute ammonia and an
excess of 1 percent hydrochloric acid added. ‘The amount of the
precipitate and the carbon, nitrogen and phosphorus in the precipt-
tate were determined as before. ‘The results obtained are recorded
in Table 21.

116 SULLETIN No. 145 [April,

TABLE 21.—PRECIPITATED Jativre Notre; CARBON, NITROGEN AND PHOSPHO-
RUS IN THE PRECIPITATED Jatieére Notre: RESULTS EXPRESSED AS
Pounpbs In Two M1,Lion Pounps oF Dry Sor,

(Soil first acid-extracted before treatment with ammonia)

Carbon in | Nitrogen in |Phosphorus in
Number Precipitated | precipitated | precipitated | precipitated
Maticre Noire Maticre Noire Matiire Notre Maticre Notre
A - 30110 1410 | ~~ -:1242 57
B 31140 ain Usteys' 1198 56
Average 30625 11482 | 1220 | 56

ol

Phosphorus-nitrogen ratio = 1 :21.7
Nitrogen-carbon ratio = 1:9.5
Phosphorus-carbon ratio = 1:205

Table 22 summarizes the results reported in Tables 20 and 2r.
Of the total dissolved matiére noire only 50 percent was precipi-
tated. Again the greater part of the carbon and nitrogen remain
in the mother liquor. Only 44.5 percent of the carbon and 42.9
percent of the nitrogen were precipitated while but 8.7 percent of
the phosphorus was precipitated.

TABLE 22.—Matiére Notre; CARBON, NITROGEN AND PHOSPHORUS PRECIPI-

TATED FROM AMMONIACATL SOLUTION BY HYDROCHLORIC ACID: RESULTS
EXPRESSED AS PERCENT OF TOTAL SOLUBLE IN AMMONIA

(Soil first acid-extracted before treatment with ammonia)

Matiire Noire| Carbon Nitrogen | Phosphorus
50.0 44.5 42.9 Ba

Again, the question regarding the source of the phosphorus
remaining in solution arises. It will be seen that 55.6 percent of
the soluble carbon and 58.1 percent of the soluble nitrogen also re-
main in solution. Attention should be called to the fact that when
the original soil was treated direct with ammonia, without previ-
ous extraction with hydrochloric acid, under conditions where the
maximum amount of inorganic phosphorus should be dissolved,
only 238 pounds of phosphorus per two million pounds of soil
were obtained: yet, after the soil had been treated with hydro-
chlorie acid to remove the calcium, under conditions where the
minimum amount of inorganic phosphorus would be dissolved by
ammonia, 516 pounds of phosphorus per two million pounds of
soil were obtained. ‘The difference between these two numbers,
278 pounds, unquestionably represents phosphorus which must have
been derived from organic sources. Now, since only 55 pounds of
phosphorus is precipitated with the matiére noire by hydrochloric
acid, it would appear that the organic phosphorus associated with
the precipitated matiére noire 1s only a very small part of the or-
ganic phosphorus present in the soil.

1910] 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 matiére noire in quantity for analysis would
cause a decomposition of the phosphorus compounds; hence when
the matiére noire is redissolved and precipitated by hydrochloric
acid, less phosphorus would 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 matiére notre 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 MWVatiere Noire: RESULTS Ex-
PRESSED AS POUNDS PER Two MILLION PouNDS OF Dry Sor,

Soil not acid-extracted Soil acid-extracted

Phosphorus | Phosphorus | Phosphorus | Phosphorus |Phosphorus
Number| in heated |in unheated | in heated |in unheated | in barium
Matibre Notre\MaticreNoire|Matiere Noire| Matitre Noire| precipitate

A 20 61 56 133 133
B 18 77 Sy oat ee 138
Average 19 69 56 LS ane | 135

The acid extracted soil gave similar results: the precipitated
matiére noire which had been subjected to heat gave only 55
pounds of phosphorus per two million pounds of soil, while the
precipitated matiére 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 by the decolorizing of the supernatent liquid and by
the fact that evaporation of the filtrate and ignition of the residue
gives only a very 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 organic sources. The results
are recorded in the last column of ‘Table 23 and compare very well
with those previously obtained.

According to Schmoeger, extraction of the soil for 24 hours
with 12 percent cold hydrochloric acid removes all of the inorganic
phosphorus readily soluble in dilute acids. Would not such treat-
ment also. remove any inorganic phosphorus readily soluble in
dilute alkali? It would certainly seem that the subsequent extrac-
tion with dilute ammonia of the acid extracted residue ought to
dissolve only organic phosphorus. ‘This idea was confirmed by ex-
perimental evidence and thus additional information regarding the
nature of the ammonia-soluble phosphorus was obtained.

Two samples of 10 grams each of the soil under consideration
were extracted for 24 hours with 100 ¢.c of 12 percent cold hydro-
chloric acid, then filtered and washed with hot water until the fil-
trate was free from chlorides. One of the samples was then
extracted with 4 percent ammonia for 36 hours in the usual way
and the amount of ammonia-soluble phosphorus determined: the
second sample was again extracted with 12 percent cold hydro-
chloric acid for 36 hours and the amount of soluble phosphorus
determined. Both experiments were duplicated. The dilute am-
monia extracted 540 and 570 pounds of phosphorus or an average
of 555 pounds of phosphorus per two million pounds of soil which
had previously been extracted with cold 12 percent hydrochloric
acid, while a second extraction with cold 12 percent hydrochloric
acid yielded only 94 and 96 pounds 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 12 percent hydrochloric acid removed some
organic phosphorus since Berthelot and André (31) have demon-
strated that organic matter of the soil is somewhat soluble in this
reagent.

It would also seem very unreasonable to suppose that dilute
ammonia possessed as great a solvent power for inorganic phos-
phorus as does 12 percent cold hydrochloric acid. But, assuming,
for the sake of argument, that only inorganic phosphorus is ex-
tracted by the hydrochloric acid and that dilute ammonia has as
ereat a solvent power for inorganic phosphorus as the hydrochloric
acid, the above experiments seem to demonstrate that at least
460 pounds of phosphorus (555-95) of the ammonia-soluble phos-
phorus has been derived from organic sources and that at least
83 percent of the ammonia-soluble phosphorus has been derived
from organic sources.

1910] Carbon, PHospHoRUS AND NITROGEN IN SOILS 119

(c) ORGANIC PHOSPHORUS BY SCHMOEGER’S METHOD

The second method for determining the organic phosphorus is
the one proposed by Schmoeger. Eggert, Nilson, ache and others
have shown that simple ignition increased the solubility of the
phosphorus in cold hydrochloric acid. ‘The increased solubility of
the phosphorus was believed to be due to the destruction of the
organic phosphorus compounds. ‘Therefore, the amount of phos-
phorus in the original soil, soluble in cold hydrochloric acid, sub-
tracted from the amount in the ignited soil soluble in cold
hydrochloric acid of the same strength was regarded 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 140°-160°C. ‘This treatment of
the soil decomposed 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 by both of
the above methods. ‘Thus, 10 grams of the original soil was
treated with 100 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. At 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 soluble in 12 percent cold hydrochloric acid while
there are 814 pounds in the ignited soil soluble 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 140-145 C. The sample was then digested for 24 hours
with cold hydrochloric acid, filtered and the filtrate made up to
500 c.c. An average of two determinations show that 878 pounds
of phosphorus were obtained. This would indicate that there were
607 pounds of organic phosphorus in two million pounds of the
surface soil. Slightly higher results for organic phosphorus are thus

120 Butietin No. 145 [April,
obtained by the autoclave method but it 1s probably more nearly
correct since it is difficult to conceive how the treatment in the
autoclave would render any inorganic phosphorus soluble which
would not be rendered soluble by ignition while the work of Leav-
itt and LeClere (81, 82) would indicate that ignition might render
some of the organic phosphorus 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

TABLE 24.—PHOSPHORUS SOLUBLE IN TWELVE PERCENT HYDROCHLORIC ACID:
RESULTS EXPRESSED AS POUNDS IN Two MILIIon PouNnDs oF Sor,

Original | Ignited | Organic
Number soil soil phosphorus
A 266 819
B 276 809
Average 271i 814 543

TABLE 25.—PHOSPHORUS SOLUBLE IN TWELVE PERCENT HyDrRocCHLORIC ACID:
RESULTS EXPRESSED AS POUNDS IN [wo MILLION POUNDS OF SOIt,

Original Evaporated

Organic

Number soil soil phosphorus
A 266 876
B 276 880 _
Aver age) eat 878 | 607

Schmoeger’s method 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. ‘Table 26 gives the sum-

marized results of the organic phosphorus obtained by the several

methods.
TABLE 26.—'Torar, PHOSPHORUS AND ORGANIC PHOSPHORUS BY SEVERAL,

METHODS

Organic phos- Organic phos-
Organic phos- | phorus by solu-|| Organic phos- ||phorus by evap-
phorus by cal- tion in dilute phorus by ig- oration
culation ammonia nition (Schmoeger)
‘Pounds | Pounds Pounds Pounds
Total ||pertwo| Per- ||pertwo| Per- ||pertwo| Per- ||pertwo| Per-
phos- |) million | centof)| million | cent of|; million | cent of|| million | cent of
phorus |) pounds total || pounds} total || pounds} total || pounds | total
|| of soil | of soil of soil of soil
919 || 423 46 504 55 543 60 607 66

1910] CARBON, PHOSPHORUS AND NITROGEN IN SOILS 121

CONCLUSIONS

1. The phosphorus-nitrogen ratio in the surface soil of the
brown silt loam soils is 1:13.5 while the same ratio in the black
clay loam soils is I :11.4.

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 equal to the ratio of the more common proteins contained in
the humus 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 in the surface, sub-
surface, and subsoil respectively.

The ratios in the black clay loam soils are 1:11.7, 1:11.9 and
1:9 in the surface, subsurface, and subsoil respectively.

4. The phosphorus-carbon ratio in the surface soil of the
brown silt loam is 1:165.2 while the ratio in the surface soil of the
black clay loam soils is 1 :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 matiére noire in quantity for analy-
sis, causes a hydrolysis of the organic phosphorus compounds.

7. The determination of the phosphorus associated with the
precipitated matiére 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.

rgr0| CARBON, PHOSPHORUS AND NITROGEN IN SOILS 123

NI

0.

LO,

Ne

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