44 2
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
decomposed organic matter. With the former the recovery was 97.62 per cent and with the latter, after allowing for the 1.80 per cent of inorganic carbon dioxide in the sample, the recovery was 99.44 per cent. The sample of Caribou loam is a n example of a soil with a n abnormally large amount of acid-soluble or; ganic matter. The ammonium carbonate modification gave 33 per cent higher results on this soil t h a n Method A, recovering 1.60 per cent of the acid-soluble organic matter, which is z 5 per cent of the organic matter of the soil. It is believed b y the writer t h a t the method and its modifications here proposed will indicate the organic matter content of the soil t o within 3 per cent in per cent of organic matter and within the limit of experimental error with the average mineral soil. The question of the carbon content of soil organic matter will be studied further. The writer is indebted t o Dr. G. S. Fraps, Dr. E. C. Shorey, and Mr. De F. Hungerford for some samples of soils, and t o Mr. R. H. Ridge11 for assistance in the analytical work. SUMMARY
The minerals in the soil which interfere with the accuracy of the loss-on-ignition method for the determination of organic matter can be removed by digesting in the warm with a weak acid solution containing hydrofluoric and hydrochloric acids without dissolving more t h a n a small amount of organic matter. This fact has been made the basis of a method for the determination of organic matter in soils which is much superior t o the loss-on-ignition method and is believed t o be superior t o the organic carbon method. ARKANSAS AGRICULTURAL EXPERIXENT STATION FAYETTRVILLE, ARXANSAS
THE AGRICULTURAL AVAILABILITY OF RAW GROUND PHOSPHATE ROCK1 By WILLIAMH. WAGGAMAN AND C. R. WAGNER Received April 16, 1918
INTRODUCTION
The present shortage and high price of soluble phosphate is one of the most serious problems which confronts the agricultural interests of this country. The fact t h a t the munitions industry calls for immense tonnages of sulfuric acid which are normally used in the manufacture of superphosphates makes i t appear unlikely t h a t the price of this latter material will decrease or its tonnage be much increased in the near future. While a t least zoo patentsZ have been issued dealing with methods of producing soluble and available phosphates, without the use of sulfuric acid, either these have been proved commercially impracticable or their adoption would involve too much time t o prove of immediate value. There is, therefore, a very urgent demand for a phosphatic fertilizer which will meet in part, a t least, the present emergency, and raw ground rock phosphate is the only material which can This article is a summary of an exhaustive investigation of the subject made by the Bureau of Soils. The details of this investigation will appear in a later publication. 2 U. S. Department-of Agriculture, Bull. 812 (1915). 1
Vol.
IO,
No. 6
be produced in sufficient quantities t o make up this serious shortage. The value of raw ground rock phosphate as a fertilizer has been a much-discussed question for over fifty years. Some agronomists and agricultural chemists have reported satisfactory results from its use both in pot and field experiments. Others have decided t h a t while the material is beneficial t o a number of crops when applied under certain conditions, i t is so inferior t o acid phosphate t h a t i t is unwise under normal conditions t o depend upon it as a source of phosphoric acid, when one can obtain more soluble superphosphates. Still others have concluded t h a t raw ground phosphate is entirely unprofitable on most of the soil in their particular States under their present crop systems. I n spite of the many adverse opinions regarding its value, however, the use of finely ground, raw rock phosphate has continued t o increase until now the annual consumption is over 65,000 tons involving a n expenditure of over $j?o,ooo. T H E NATURE “OF MINERAL PHOSPHATES
I t is not within the scope of this paper t o discuss in detail the nature and origin of phosphate deposits, but the main constituent of most of the amorphous phosphate rock is tricalcium phosphate, a compound which is relatively insoluble in water and quite resistant t o weathering influences. I n fact the formation of phosphate deposits may be said t o be largely due t o the slight solubility of this latter c0mpound.l A quick response from applications of such material, therefore, is hardly t o be expected unless i t is subjected t o some treatment b y which its solubility is considerably increased, or is applied t o the soil under such conditions t h a t i t will yield its phosphoric acid t o the soil waters approximately as fast as it is taken u p by growing crops. I n order t o render t h e phosphoric acid in phosphate rock soluble and facilitate its distribution in the soil, i t was proposed t o treat t h e material with sulfuric acid. This method was first practiced on bones and bone products about IOO years ago and since then the use of acidulated phosphates has grown rapidly until now the vast bulk of the phosphate rock entering into the fertilizer industry is treated with sulfuric acid and manufactured into superphosphate. I t must be admitted, however, t h a t most of t h e phosphoric. acid contained in practically all productive soils is in the form of relatively insoluble phosphates of lime, iron and alumina, yet many of these soils continue t o yield large crops without the addition of any soluble phosphates and frequently give no response t o such applications.2 The question is, therefore, will raw rock phosphate increase the yield of crops when applied under proper conditions and if so, is the increase obtained commensurate with the cost of the material? 1 Eliot Blackwelder, “The Geologic Rble of Phosphorus,” Scientilic American, Supplement No. 2197, Feb. 9 , 1917. 2 The fact is particularly well exemplified in the “Blue Grass” regions of Kentucky and in the “Central Basin,” Tennessee, where the soils are very high in phosphoric acid.
June, 1918
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
E F F E C T OF F I N E GRINDING AND ORGANIC FERMENTATION ON
THE
SOLUBILITY
AND
AVAILABILITY
OF
PHOSPHATE ROCK
N o one questions the fact t h a t fineness of division facilitates the solubility of mineral matter. Relatively insoluble substances, such as tricalcium phosphate, when in the precipitated conditions dissolve quite appreciably in water as well as in certain conventional solvents, such as ammonium citrate and 2 per cent citric acid. I t has also been repeatedly demonstrated both in laboratory and greenhouse experiments t h a t the solubility of raw rock phosphate is considerably increased b y fine grinding.' Not only is the distribution of the rock in the field much facilitated in this way, but an enormous surface of the mineral is thus exposed t o the solvent action of the soil waters. I n the early experiments conducted with this material strict attention was probably not given t o this important factor and i t is very likely t h a t a great deal of work with raw rock phosphate resulted adversely on this account. Several companies offer raw phosphate rock for sale guaranteeing go per cent t o pass a sieve of zoo meshes t o the linear inch. While tests performed in this laboratory seem t o show t h a t i t is hardly feasible t o put rock of this degree of fineness on the market a t a low. price, i t is entirely possible t o grind the material so t h a t go per cent would pass a IOOmesh sieve, and material of this degree of fineness should prove quite effective. Because raw ground rock phosphate has in many cases proved more effective on soils rich in organic matter or when applied in connection with stable manure, i t has been suggested t h a t certain organic acids in the soil exert a solvent influence on the rock similar t o the effect produced by sulfuric acid. The existence of organic acids in t h e soil in quantities sufficient t o appreciably effect the solubility of phosphate rock is doubtful, but soils of high organic content are always rich in carbon dioxide and bacteria, both of which have a n important influence on the solubility and alteration of soil minerals,2 and hence i t is reasonable t o expect a n increase in the solubility of the phosphate contained therein over t h a t of soils of low organic content. Other things being favorable, therefore, it appears t h a t soils low in phosphoric acid and rich in organic matter should respond readily t o additions of raw rock phosphate provided t h a t the material is very finely ground, applied liberally, and is well distributed by thorough cultivation. WORK O F T E E E X P E R I M E N T STATIONS
The experiment station literature contains the results of 232 field experiments and 23 pot experiments 1 J. A. Voelcker, J . Roy. A g r . Soc., 4 (1868), 176-196; W. H. Jordon, N. Y.Exp. Sta. (Geneva), Bull. S58 (1913); W. .,I Burlison, J . A g v . Res., 6 (1916), 507-8. 2 C. P. Williams, Chem. News, 24 (1871), 306, T. Schloesing, Comfit. rend., 131 (1900), 149; P. Kossowitch, Biedermann's Zentr., 32 (1902), 44-49, E. Truog, Wis. Exp. Sta., Reseavch Bull. 20 (1912); Sackett. Patten and Brown, Mich. Exp. Sta., Bull. (Special) 43 (1908); Tottingham a n d Hoffman, Wis. Exp. Sta., Reseavch Bull. 29 (1913), 213-312; C. A. Mooers, THISJOURNAL, 6 (1914), 487-8; Fred and Start, Wis. Exp. Sta., Bull. S5 (1915), 35-66; Hopkins and Whiting, Ill. Exp. Sta., Bull. 190 (1916), 395-406.
443
conducted with raw rock phosphate, yet unless the relative merits of these experiments are very carefully weighed they cause the reader much confusion and lead t o the conclusion t h a t raw rock phosphate is of very questionable agricultural value. It is now a generally accepted fact, however, t h a t field experiments must be conducted for a period of several years before the results can be seriously considered, so after a careful study of the work recorded by the stations, the writers decided t o give detailed consideration only t o those field experiments which were conducted for j years or longer. This method of treatment has eliminated 195 field experiments, of which number, 144 were conducted for I year only, 2 1 for 2 years, 19 for 3 years and 11 for 4 years. The remaining 37 experiments (conducted for 5 years or longer) were then given detailed study, careful attention being paid (as far as possible) t o the following important factors which influence the results of field work: ( I ) Uniformity of experiment field. ( 2 ) Topography and drainage conditions. (3) Chemical and physical composition of the soil. (4) Previous treatment of the field. (5) Climatic conditions. (6) Injuries from disease, insects, and animals. (7) Kinds of crops grown and selection of seed. (8) Rate of application and uniform distribution of phosphates. ( 9 ) Methods of comparing raw rock with other phosphates. ( I O ) Effect of other fertilizers. (11) Number and distribution of plots. ( I 2) Duration of experiment. I n most cases many of these factors were not recorded in the descriptions of the experiments, and since the work was conducted under such a variety of conditions and with so many objects in view i t could not be reduced t o a common basis for the sake of comparison. The details of these experiments will be discussed in a subsequent publication, but a summary of the results obtained is given below in Table I. I t must be borne in mind, however, t h a t the classifications made are necessarily somewhat arbitrary since it is impossible t o summarize the results of field work in such a way as t o give each experiment its proper weight. Out of the 37 tests given in Table I, 2 2 were carried on with a view t o comparing the relative merits of raw rock and acid phosphate. The conditions under which such a comparison was attempted varied greatly, but i t may be said t h a t in a general way, 13 of these experiments or 5 9 . 1 per cent gave crop yields as favorable t o raw rock as t o the more soluble form of phosphoric acid. Of the 9 experiments in which raw rock did not compare favorably with acid phosphate, z were conducted on fields unresponsive t o phosphate treatments and 2 gave results which could be classed as either favorable or unfavorable, depending on the method of interpretation employed. Of the 1 5 experiments in which no comparison between raw ground rock and acid phosphate was attempted, 1 1 , or 73.3 per cent, gave results strongly indicating beneficial effects from the applications of t h e former material, and 2 of the remaining 4 experiments were conducted on fields showing little or no response t o phosphate treatment.
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
444 TABLR I-SUMMARY
STATE
Total No. of Expenments
. ... .. .. .. ...... ......... ......... .. ii
Ala.. Conn., Del.. Fla.. Ga. ......... 111.. , , , . , ,
Ind. . . . . . . . . 2 Ky . . . . . . . . . La., . . .\. Me.. . . . . . . . Md.. Mass. Miss.. Mo..
No. hTo. favor- unfavTotal able orable
. . . . . .
. . .. .. .3 . 2
.. 4 1 1 0 0 l(a)
Va.. . . . . . . . . Wash.. . . . . . . . W. Va.. . . . . . . Wis.. . . . . . . . . .
TOTAL.. ....
No. 6
EXPERIMENTS W I T H RAWROCKCONDUCTED BY T H E S T A T E S T A T I O N S OVER P E R I O D S O F F R O M 5 TO 20 Y E A R S Experiments com- Experiments making no Experiments where Experiments where Experiments where raw Apparent paring raw rock comparison of raw rock raw rock applications raw rock applica- rock was used in conneccumulative with acid phosphate with acid phosphate were relatively light tions were liberal tion with organic matter effect
. . . . .. .. .. .. .2 ' i ( a ) 1
'i
0
IO,
O F RESULTS OF FIELD
....
....... ....... ..... ....... N . J ........ N . Y ........ N . C ........ Ohio.. ...... Pa.. ........ R . 1........ s.c........ Tenn ........
Vol.
1 2 1 1
..
l(u) 1 2 1
.. .. ..
. . . . . . 2 1 i(b) 1 1 .. 1
. . . . . l(e). . . -
.. . . . . . . . . . l(U) . . . .. .-. . -. 1
No. No. favor- unfavTotal able orable
.. .. .
9
.. .. .
.. .. .. .. . . 7
.. ..
.. ..
. . . .
..
No. No. favor- unfavTotal able orable
.. ..
.. . .
. . .4 . .2 . 2
..4
.. 2
.. ..2
.. ..
.... ..
.. .. ..
,.
..
.. *2.
.1 . 2
..4 ..
.. . .
.. . .
.. . .
.. . . . 4 . . ... . . . . . . .2 .. ... . 21. . .. 2 .. .. 2 .. .. 2..
'2
.. .. ..
..
.. -
.. l(a) .. ... ... -
... ... .. .. .-.
.. l(U) .. .. .. . -.
No. hTo. favor- unfavTotal able orable
.. ..
.. ..
.. ..
. . . . . .
. . . . . .
.-
-
No. No. favor- unfavTotal able orable
.. . .
.. ..
.. ..
.. ..
.. ..
.. ..
CONCLUSIONS
After carefully weighing the results of all laboratory, field and greenhouse experiments with raw rock phosphate the writers feel t h a t the following general conclusions are justified: I-Field experiments conducted for only one or two years, where the various fertilizer treatments are not replicated or where no index is given t o the relative natural fertility of the various plots employed, have little or no meaning. 2-Liberal and even medium quantities of raw rock phosphate t o most soils produce a n increase in the yields of many crops the first year of its application.
%
-
. . . . . .
. . . . . . . . . . . . . . . . . . '8
'i
.2 . 1 .. .. . . .. .. 1 . . .. ..
. 2. 1 .. .. . . . . . . 1 . . .. ..
.. .. . . . . . . .. . . .. ..
.1 . 1 .4 . .. .. . .
. i .. .. 1 .. .2 ' 2 . . . . . . . . . . . . . 3 . . ... . . . . . . . . . . . .
. . . . . .
.3 .. .
. . . . . . _. . .- . -. .
. . . . . . . . .-. . -. -
. . . .
37 22 13 9 15 11 4 21 15 6 16 13 3 23 18 5 (e) Soil not responsive to phosphate treatment. ( b ) Figures for this experiment are favorable according t o one method of computation and unfavorable according t o another.
I n 2 1 experiments the applications of raw rock were relatively light ( 2 5 0 lbs. or less per acre), yet 15 of these experiments, or 71.4 per cent, showed distinctly favorable increases in yields on the fields treated with this material. I n 16 experiments where the raw rock applications were more liberal, 13, or 81.3 per cent, resulted favorably t o raw rock phosphate, and the remaining 3 experiments were conducted on soils showing little or no response t o phosphate treatment. Raw rock phosphate was applied in connection with organic matter in 23 experiments. Out of this number, 18, or 78.3 per cent, gave distinctly favorable results, and of the 5 remaining experiments 3 were conducted on fields unresponsive t o other forms of phosphoric acid. In regard t o the cumulative effect of raw ground phosphate rock i t may be said t h a t in 17 instances (46 per cent of the entire number of experiments) there was evidence of greater availability after raw rock had been applied for a number of years. In 13 out of the remaining 2 0 experiments the data are not sufficient to give evidence on this point, and in 4 out of the 7 cases where no cumulative effect was shown the soils were not responsive t o phosphate treatments.
r
EviUn dent None known No. No. No.
1 1
.. 4
.. .. ..
1
..1 .. .. .. .. 17
. . . .
. . . . . . . . . . . .
..1
3
..
. . . . . . . .
..l(u) . . . . . . . . . . .- . .-. I
7
.
13
3-The effectiveness of raw rock phosphate depends largely on its thorough distribution in the soil, this distribution being brought about b y liberal applications of very finely divided material and thorough cultivation. 4-The presence of decaying organic matter in the soil increases the effectiveness of raw ground rock phosphate, due probably both t o greater bacterial activity and the higher content of carbon dioxide in such soils. 5-As a corollary of 3 and 4, the effectiveness of raw rock phosphate is usually increased after remaining in the soil for a year or more. 6--Most crops respond more quickly t o applications of acid phosphate t h a n t o bone, basic slag, or raw rock phosphate. Therefore, where the early stimulation and quick maturity of the crop are the main consideration, acid phosphate is probably the best form of phosphoric acid t o apply. 7-Field experiments in which raw rock and acid phosphate are compared on the basis of equal applications of the two materials or on equal applications of phosphoric acid in the two forms result often in favor of acid phosphate (particularly when such experiments are conducted for a short period), since in order t o get the maximum benefit from the natural phosphates they must be applied a t a rate far exceeding t h a t a t which acid phosphate proves effective. 8-The question whether increases in yield can ordinarily be produced more economically by applications of the soluble or relatively insoluble phosphates must be considered in a measure a separate problem for each farmer, since i t depends on a number of factors of which the most important are the nature of the soil, the crop system employed, the price of the various phosphates in each particular locality, and the length of the growing season. BUREAUOF SOILS DEPARTMENT OF AGRICULTURE WASHINGTON, D. C.
