TEXAS AGRICULTURAL EXPERIMENT STATIONS. BULLETIN NO. 126. Chemical Section, November, 1909. Active Phosphoric Acid and its Relation t0 I the Needs of the Soil for Phosphoric Acid in Pot Experiments BY G. S. FRAPS, Chemist. POSTOFFICE COLLEGE STATION, BRAZOS COUNTY, TEXAS. AUSTIN, TEXAS; VON BOECKMANN-JONES 00., PRINTERS. 1910 TEXAS AGRICULTURAL EXPERIMENT STATIONS GOVERNING BOARD (Boum or DIRECTORS A_ AND 1L COLLEGE.) K. l\'. LEGErr, President . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Abilene T. D. ltmvELL. \l'ice-President . . . . . . . . . . . . . . . . . . . . . “Jefferson A. HAIDESEK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .LaGrange J. M. (lnElax . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .Yoakun1 W-\1.'ro.\' PETEET‘ . . . . . . . . . . . . . . . . . . . l . . . . . . . . . . . .Fort Worth E. R. KOXE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Austin A. R. MoCoLLlvn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Wat-o W. P. SEBASTI.»L\* . . . . . . . . . . . . . . . . . . . . . . . . . . . . Breckenridge PRESIDENT OF THE COLLEGE. R. T. MILXEI: . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . (‘ollcge Station STATTION O F ltlCERS. H. H. Hmmxerox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Director W, C. WrtLnorzY . . . . . . . . . . . . . . . . \’1'ce Director and Agriculturist J, W. Clmsox‘ . . . . ..-\ssistant to Director and State Feed Inspector M. lfltxxols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Veterinarian G. ERAPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Chen1ist J. C. BURNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .."\nin1al. Husbandry H. NESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Horticulturist RAYMOND H. Pom) . . . . . . . . . . . . . . . . . . . . . . ..Plant Pathologist WILMoX XEWELI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..iEnton1ologist H. L. MOKNIGHT . . . . . . . . . . . . . . . . . . . . . ..\ssistant Agricnltnrist N. (l. HAMNER . . . . . . . . . . . . . . . . . . . . . . . . . . . ..-\ssistant (‘hemist J. B. RATHER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Assistant (“hemist E. C‘. CARLYLE . . . . . . . . . . . . . . . . . . . . . . . . . . . “Assistant Cfhemist P. W. CIUSLER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Chiet Clerk F. R. l\'.\\*-\II.L1-: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..Stenographer A S. WARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . “Stenograplwcr XOT*E.—T/'I(? Jl-airt Station is located on the ground of the .4_(_/1't-- cultural and Jlccloanical College, in Brazos county. The f/ostofice address 1's College Station, Texas Reports anrl bulletins are sent upon (application to the Director. S'an2]1le.<~ s-houl/l not be sent for analysis zoithozlt [Irerious correspondence. STATE AGRICULTURAL EXPERIMENT STATIONS. GOVERNING B OARD . His Excellency, Govicuxon T. M. CAMPBELL. . . . . . .Austin, TPQx-as. Lieutenant Governor, A. B. DAVIDSON . . . . . . . . . . . . .Cuero, 'l‘exas. Commissioner of Agriculture, Hox. E1). R. IQONE, Austin, Texas. DIRECTOILOF STATIONS. H. H. HARRINTHTWLY . . . . . . . . . . . . . . . . . . ..(.‘ollege Station, Texas. SUPERINTICNDEXTXS OI“ SiFATYIOXS. A. T. T)O'I‘TS, Beeville Station, Beeville, Bee county, J. L. WisLcii, Troupe Station, TFOUpG, Smith county. W. S. HOTCHKISS, Lubbock Station, Lubbock, Lubbock county. J. T. CRUSE, Fort Worth Stat-ion, Fort- Worth, 'I‘arrant county. J. H. 'l‘o.u, Pecos» Station, Pecos, Reeves eountv. H. C. HOL31i2sjl3er1ton Station, Denton, Denton county. ~ —-———-_ Teiu )I9 Station Tein le Bell countv. . I I) 1 . I. S. YORK, Spur Station, Spur, Dickens county. , Angleton, Station, Angleton, Brazoria county. J. K‘. FITZGERALD, Beaumont Station, Beaumont, Jefferson county. man TEXAS AGRICULTURAL EXPERIMENT STATIONS. AVAILABLE BULLETINS. The following is a. list of Bulletins of this Experiment Station available for distribution. The others are out of print. Any of these Bulletins will be sent free of charge. Requests should be di- rected to the Director of the Experiment Station, College Station, Texas, " 79. Cotton Breeding. 81. Tomato Fertilizers at Troupe. 88. Munson’s Bulletin on Grapes. 90. The Feed Control in 1905-06. 91. Food Adulteration in Texas. 92. A Test of the Producing Power of Some Texas Seed Corn. 96. Commercial Fertilizers and Poisonous Insecticides, 1906-07. 97. Kaffir Corn and Milo Maize for Fattening Cattle. 98. Summary of all_Bulletins from No, 1 to 94, inclusive. 99. The Composition and Properties of Some Texas Soils. 100. Chemical Composition of Some Texas Soils. 102. Texas Honey Plants. 104. Digestion Experiments. 105. Notes on Forest and Ornamental Trees. 107. Commercial Fertilizers and Poisonous Insecticides, 1907-08. 108. Winter Bur Clover. 109. Alfalfa. 110. Steer Feeding Experiments. 111. Texas Fever. 112. Nature and Use of Commercial Fertilizers. 113. Spray Calendar. 114. Composition of White Lead and Paints. 115; Fertilizer Test with Onions, 117. Commercial Feeding Stuffs in 1907-08. 119. Infectious Anaemia of the Horse. 120. Corn and Cotton Experiments for 1908. 121. Report of Progress at the Troupe Substation. 122. The Effect of Salt Water on Rice. 123. Commercial Fertilizers and Poisonous Insecticides, 1908-09. 124. The Pecan Case-Bearer, 125. Chemical Composition of Some Soils of Angelina, Brazoria, Cameron, Cherokee Delta Lamar, Hidalgo, Iiavaca, M ont- gomery, Nacogdoches, Robertson. Rusk, Webb, and Wilson counties. First, Second, Fourth, Fifth, Eighth, Ninth, Tenth, Eleventh, Twelfth, Thirteenth Annual Reports. H. H. HARRINGTON, Director. TABLE OF CONTENTS. PAGE. Factors of Availability of Plant Food . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 7 Methods of Estimation of Phosphoric Acid . . . . . . . . . . . . . . . . . . . . . . . . .. 8 Analysis by Weak Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8 Methods of Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 9 Factors Influencing the Composition of the Soil Extract . . . . . . . . . . . . .. 10 Solubility of Mineral Phosphates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11 Fixation of Dissolved Phosphoric Acid . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . 15 Relation of Fixation to Composition of Soil . . . . . . . . . . . . . . . . . . . . . . 17 Fixation by Soil Residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18 Extraction of Absorbed Phosphoric Acid . . . . . . . . . . . . . . . . . . . . . . .. 20 Relation of Fixing Power of Soil to Absorption from Fifth-Normal Nitric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 23 _ Importance of Fixation in Soil Analysis . . . . . . . . . . . . . . . . . . . . .. 25 Successive Extractions of Natural Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 25 Effect of Sulphate of Lime. . ..' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 30 Solubility of Constituents of the Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31 Acid Consumed . . . . . . . . . . . . K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 32 Percentages Dissolved by Weak Solvents . . . . . . . . . . . . . . . . . . . . . . .. 33 Effect of Successive Extractions . . . . . . . . . . . . . . ..'. . . . . . . . . . . . . . . . . . .. 35 Relation of Citric to Nitric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 36 Significance of the Phosphoric Acid Dissolved by Weak Acids . . . . . . . . .. 38 Relation of Pot Experiments to Active Phosphoric Acid . . . . . . . . . . . . .. 39 Conditions Which Affect Production in Pots . . . . . . . . . . . . . . . . . . . . . . .. 40 Method of Conducting Pot Experiments . . . . . . . . . . . . . . . . . . . . . . . .. 41 Relation of Deficiencies of Crops to Active Phosphoric Acid . . . . . . . . . . . 42 Relation of Active Phosphoric Acid to Weight of Crop . . . . . . . . . . . . . .. 54 Relation of Acid Consumed and Fixation to Deficiencies . . . . . . . . . . . . .. 60 Relation of Phosphoric Acid Removed by Crops in Pot Experiments to Active Phosphoric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 65 Availability of Active Phosphoric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 69 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 70 [Blank Page in Original Bulletin] ACT IVE PHOSPHORIC ACID AND ITS RELATION TO THE NEEDS OF THE SOIL FOR PHOSPHORIC ACID - IN POT EXPERIMENTS. BY G. S. FLAPS, 'I‘his is a ttichnical hulletin and intendtrd primarily for scien- tific readers. The conclusions here reported, however, are of con- siderahle popular significancti when applietl to the soil oi’ Texas. as shall he the ohject 01' a later bulletin to explain. The Work here presented talls naturally into two parts. 'lfhe first part deals with the ]1ll()Spl10I‘l(‘ acid in the soil. and zittempts to discover the nature ot‘ the compouinls in the soil from which phos- phoric acid is dissolved hy weak zieid solvents, and the significant-e ot the extracted phosphoric acid to the chemisti'_v of the soil. The second part (leals with an extensive series of pot experi- ments, and the relation hetween the results ot these experiments. and the analysis ol‘ the soil with fifth-normal nitric acid. By “active: phosphoiic acid” we mean the phosphoric acid soluhle in fifth-normal nitric acid. In using" this term in this way we do not intend to convtfv the idea that the phosphoric acid soluhle in titth-norlnal nitric acid is all the ])l1()_'~‘1)l1()1'l(‘ zicitl ot‘ significance to the plant. ' I<‘.~\C’I‘(')IIS or .\\'.\II'..\IKII.T'[‘Y or PLANT FOOD, The amount ot any given plant tood which is withdrayvii strom the soil hy the plant docs not depend upon one condition only. hut is dependent upon and conditioned hy a numhei‘ of the factors. (ITraps, ‘Amer. (lhem, Jour. 32. 1904.) These factors may he grouped as follows: _ (l) The quantity of the element present at the heginning‘ of the growing‘ season in forms of comhin-ation which can he partly or eomiiletelv' ahsorhetl hy the plant. This may he called cliemicalti/ r/rr/Nnb/c» plant food. (2) The condition of’ the soil particles. (“oinpounds chemically zivailahle may he enclosed in the soil particles so as not to he ex- posed to the action of plant roots. Such compounds are ])7z_z/s1icr1t7]_1/ unaticrzvzi/avble. ‘If the encrusting‘ suhstance is removed. such hodies hecome chemically available. (3) The znnount of the plant food transformed during the growing“ stiason into Forms of comhinzition which can be ahsorhed hy plants. ‘llhis factor is certainly ot importziiice with respect to _8__ nitrogen; its importance in the case of phosphoric acid and potash is apparently not so great but the matter requires study. This factor may be called weathering a-vatlability, (4) The nature of the plant. Plants differ in both their capac- ity for absorbing food and their need of it. Whatever the cause of these differences, there is no doubt but that they exist. We will call this factor jahysiclogical (availability, The character of the soil, its chemical composition, the conditions which prevail during the growth of the plant, and perhaps other factors influence the amount of plant food taken up. METHODS FOR ESTIMATION OF PHOSPHORICJACID; The phosphoric acid of the soil is estimated by four groups of" methods: (1) By complete decomposition of the soil, and the estimation of all the phosphoric acid- contained therein. (2) By partial decomposition of the soil with strong hydro- chloric acid. This method indicates the wearing qualities of the soil. ( By extraction with alkaline solvents The alkali ordinarily used is ammonia. The phosphoric acid soluble in ammonia has of- ten been called “humus phosphoric acid,” and is assumed to be in organic combination and of great importance, but it appears really to come chiefly from the iron and aluminum phosphates. (4) By extraction with dilute acids. This method is proposed to estimate the phosphoric acid easily taken up by plants, so as to indicate the immediate needs of the soil for plant food. This method is the one under study in this bulletin. ANALYSIS WITII WEAK ACIDS. Dyer (Jour. Chem, Soc, 1894, p. 115) found the acidity of the root sap of a number of plants expressed as citric acid, to vary from 0.34 to 3.4, with an average of 0.91 per cent, He accordingly prop-osed as a solvent to determine the available phosphoric acid of the soil. a 1 per cent solution of citric acid. Applied to Rotham- sted soil of known history (Bulletin 106, Oflice of Experiment Stations, U. S. Department of Agriculture) this solvent gave re- sults in accordance with the produetiveness of the plots from which they were taken. The Association of Otficial Agricultural Chemists has devoted much time to this method, and modifications of it, and has adopted a provisional method involving the use of fifth-normal nitric acid. It was found that fifth-normal nitric acid gives better results than 1 per cent citric acid. ‘91112119911 9111 110 1191p 93.121 2 111 19111 12 '9'9 0031 9111 91210112 pp2 ‘1912M 111 911p1991 dn 911211, 910111109111 291119 19191191 0112. ‘111211 1912M 110 9s9111§1p 91911111109 01 91210012119 ‘11I1p 11112911 11911 9110111901p1€11 '9'9 01 1110012 pp2 ‘111201 1912M 2 110 1191p 1121119 2 111, ($110M 191110 101 p9112s s1 91111 "9121 01 p112 9.111112191111191 111001 12 111p 01 M0112 ‘9912101 31111111) 01 19 ‘lfiém P91111911) 1111M 5111311010111 19111} 9111 11° 911111991 9111 ‘1 “'p9111ns1109 p192” 101 9121:1111 9111 10 .19p11121119.1 9111 9112s p112.‘11a p112 p192 91101111901101 10 1101121111199 9111 .101 '9"9 0001 9>121f 11911 M "191111 p9p101 91q110p_ 93121 2 110 1911111 "111011 11211 11.1911 012119 ‘9111011 91111 1s931q '1) 0017 01 p912911 11191101119111 111211 191 111 99213 919211 2 1111M p91ns29u1 ‘p192 91.11111 g/N "9-9 000g .11 p‘ ppv '91110q p919dd01s 99213 19111 T3 2 01111 1109 1113 00g 11319‘ 'P911“19“°1T) 219v 2111* 11821011‘? 91101111901151 9111:1921 zsu 1101 199911 91101119111 9111 912 311111101101 91 3 'SISL"IVNV e10 SCIOHLLEIIQ '110112z112.11n911 991192.111 1011 990p 10111112 9111 ‘91109. 999111 1011 991291119 92 111999111 11201 111 9.12 119111 ‘91109 91109129129; u911g1 991211011129 10 111.101 9111 111 111999111 1111129999911 c1011 912 11' -11109 01111 191119 119111M 999201 91111, ‘9p2111 9q p1n0119 110112211211 H 101 110119911109 412111 911911901 1011 op 1 ‘111911109 9111 921121111911 1111-‘ .10 921121111911 119111M ‘91109 91109120129 111113111 101 101991151 '11 01 p1 91101101901111 910111 99011219 0s p112 ‘111911109 9111 .101 p91110s91p 121.1912 10 K111112111) 9111 9929119111 111M p192 9111 10 11131191119 9111 311192919111 ‘9p2111 901 p111~011s 110119911109 011 9911911 p112 ‘11121d 9111 10 19111 111911109 9111 9929199p 1911111 119111M 110111p1109 2 s1 1109 9111 10 110 -1p1109 9111110112 9111 12111 sp1011 ‘11011221121111911 31119sn991p 111 ‘19Kq 'p99.132 91111991 9111 9p2111 1011 92M 11011991109 9.1911M 11111 ‘s110111p11 11M011>1 9111 1111M p10992 111 1011 919M 91111991 9111 ‘11011221121111911 1 9p2111’ 92M 11011991109 9.1911111 ‘21p111 10 9110s 9111 111 12111 11111101 poo A11 '99911911119np0.1d 11M0 9111 1111M99132 91111991 9111 ‘11011221121111911 .101 p91991109 11 '29121112fi 10 91109 91109129129 111113111 9111 110 11.101921911291111 p192 911119 11199‘ 19d 1 1111M p01119111 9<19Xq p11n01 (ggg ‘g5 1911121117) p1101111112H p112. 911191101) 'po1119111 9111 111 p911210d109111 92.11 11 p112 ‘9p2111 9q 11011991109311 91111 12111 p9p1191111110991 911 ‘91109 0011 9111 1101 p9z11211n911 p192 9111 101 1 9p2111 s2M 11011991109 11911M 110s 9111 10 111019111 11M011§1 9111 1111M p109 -92 111 K1p9>112111 910111 919M 99911919111p 9111 9V ‘1109 9111 10 999211 9111 Kq 11011221121111911 K01 P991129 111911109 9111 10 1113119119 9111 111 992919911 9111 1110 p911110d 91911119110 12191111911321 12191110 10 1101121909911 9111 10 s110g 110 99191911 9111 ‘9601 111—'110_110z1101;z1z91\[ 1101 1101109111100 _ '11192 9111111 121111011-111111 1111M 9110p 119911 9211 >110M 91111 10 1111111 91111, _1()__ a few drops of hydrochloric acid, and filter into a 100 c.c. flasl Make up to volume. Phosphoric Acid.—'l‘ake 50 c.c. for phosphoric acid (do no wash out pipette with liquid, as exactly 50 c.c. must be left). Ad 10 c.c. nitric acid, make alkaline with ammonia, then slightly acic If solution is too acid or alkaline results will be poor. Add 10 t 20 c.c. molybdate solution, and (ligest at a temperature below 40 C‘. for three hours. Filter and titrate as usual for phospho-ric acic [isle the 50 c.c. remaining for the estimation of potash. - Potashi.—lVasl1 the 5O c.c. reserved above into a porcelain evapo rating dish and evaporate once with hydrochloric acid. Dissolve i1 water and acidify with hydrochloric acid sufficient to take up th basic salts formed by evaporation, and then evaporate with platinun solution after acidifying. (Tomplcte as in Moore’s method. Pro tect from ammonia. fumes at all times. A aid C'0/rzsuivn2ied.—Heat-10 c.c. of the filtrate to boiling, boil thre. minutes, titrate with N/ 1O NaOH and phenolphthalein. Make : blank on the original nitric acid solution, and calculate the per ccntage of the acid which was consumed by the soil. FACTORS INB‘L['I P phosphates (variscite and Wavellite) and the basic ferric phos- phates are comparatively slightly dissolved. It is hardly probable that ferrous phosphate (vivianite) is of common occurrence in ordinary cultivated soils, though it may exist in some soils which are not well aerated. Fifth-normal nitric acid dissolves calcium phosphates completely, but dissolves mineral aluminium phoslphates 0r basic ferric phosphates only t0 a slight extent. It thus distin- guishes between these two classes 0f compounds in the soil. Another conclusion may be drawn from this work. Apatite, phosphate rock, ferric phosphate (precipitated), aluminium phos- phate, vivianitie, and triplite are practically equally soluble. We also feel justified in saying that acid phosphate would be completely dissolved. But no one yet can claim that thesematerials possess the same value to plants. Fifth-normal nitric acid may not distin- guish. between minerals ivhieh have unequal values t0 plants. We have no solvent which would dissolve phosphoric acid from the phosphates mentioned in the same proportions as would be taken from them bv plants. What we cannot do with known mineral phosphates of known character outside of the soil we could not ex- _13_ TABLE 1. Composition of Mineral Phosphates. 1 Laboratory Number Phosphoric Acid. In soluble acids. Aluminum phosphate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35.75 Apattite, 3Ca3P2O8+Ca(ClF)2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29.55 Calcium phosphate precipitated . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43.90 Dufrenite, FC4P2OI 1 +3H2O . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . U mm Ferric phosphate, precipitated . . . . . . . . . I . . . . . . . . . . . . _ . , . . . . . 32.80 Phosphorite, Ca3P2Og +X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33.10 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.56 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34.07 Triplite, (FeMn)3P2O8 +(FeMn)F._. . . . . . . . . . . . . . . . . . . . . . . . . . 19.20 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36.70 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.20 Variscr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ _ . , . . . . . _ . . . . . . . 31.30 “ AlPO4 +ZH2O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.05 Vivianite, FOQP2OS+8HQO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.85 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . 22.78 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . 19.10 Wavellite, Al3P4O 9+12H2O . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . 10.95 “ . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.20 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 10.50 In in- solubfe residue. PWW..9NNWP99.9 ommmowmmmw~wow wwmommwowoommo Total insoluble residue. $96565 x U} Q3 @rww5®Pwr»9»wfl %!—ll\')'4g$b4%>—*l\DC>U-'H.Ox B95333 G7(n>§l\D@P*b§\]i§ _Silica in insoluble residue. TABLE 2. i Efiect of Nature of Solvent Upon Percentage lot Phosphoric Acid Dissolved. E‘ ..- 1% N/5 N/5 N/50 a3 - Citric Hydrc- Nitric Hydro- E g Acid. chloric Acid chloric sz Acid. Acid. 237 Calcium phosphate, precipitated . . . . . . . . . . . . . . . . . . . . 100 100 . . . . . . . . 100 245 Apatite, 3Ca3P2O8 +Ca(ClF)g . . . . . . . . . . . . . . . . . . . 25.5 100 100 47 710 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 . . . . . . . . 727 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . 100 . . . . . . . . 239 Phosphorite, Ca3P208 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 100 100 85 713 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 . . . . . . . . 729 " . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 . . . . . . . . 236 Aluminium phosphate, precipitated . . . . . . . . . . . . . . . . . . 100 100 . . . . . . . . 100 716 Variscite, AlPO4+2H2O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.7 . . . . . . . . 732 “ . . . . . . . . . . . . . . . . . 1.3 . . . . . . . . 3.0 7.5 4.8 4.8 . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. 238 Ferric phosphate, precipitated . . . . . . . . . . . . . . . . . , . . . . 100 100 . . . . . . . . 16.0 241 Viviamte, Fe3P2O8 +8H2O . . . . . . . . . . . . . . . . _ . . . . 94.8 100 97.8 36.0 712 “ . . . . . . . . . . . . . . . . 98.0 . . . . . . . . 733 “ . . . . . . . . . . . . . . . . . 91.0 . . . . . . . . 242 Tripli . . . . . . . . . . . . . . . . . . . . . . .7 . . . . . . . . . . . . . . . . . . . 25.0 98.8 99.5 41.2 719 “ (FeMn)3P2O., +(Fe1l11n)F2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97.6 . . . . . . . . 724 “ __ . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . , . . . . . . . . . . . . . . . . _ . . . . 82.0 . . . . . . . . 244 Dufrenite, FQPQOU +3H¢O . . . . . . . . . . . . . . . . . . . . . . 2.0 4.0 1.5 2.0 714 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 . . . . . . . . 728 “ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . 8.0 . . . . . . . . N / 200 Hydro- chloric Acid. __14_ pect to do with the same phosphates after they are put into the soil and with unknovvrn mixed phosphates already within the soil. Soils may, therefore, contain equal quantities of phosphoric acid soluble in fifth-normal nitric acid, and yet give up unequal quan- tities of phosphoric acid to plants on account of differences in the phosphates present, This consideration must give rise to caution in comparing the results of all kinds of soils with one another. Only those soils should be rohzpared ichich probably contain the same hrinds of phosphates. Soils widely dissimilar in origin and character should not be compared, unless there is evidence that they contain similar phosphates. Efiect 0f Charcictci' of the blolirent.——'l‘lie results secured with solvents other than fifth-normal nitric acid appear in Table 2. Fifth-normal hg/(l/rocihloric acid appears to have nearly the same solvent power as fifth-normal nitric acid. One per cent citric acid has a somewhat lower solvent power, particularly for apatite and triplite. Fifth-nornzzil lz_yd1'0c"liilo1'i(; acid is characterized by :1 much lower solvent power for "ferric phosphate. vivianite, and triplite than citric acid. It does not (lissolve the calcium phosphates so well as the fifth-normal nitric acid, but to a greater extent than the citric acid. Til‘O—lltl’lli(ll'(?(llll.410W)?(ll l'!y(l'7‘OClIl07‘l( HClCl, as might he expected, falls much lower in solvent power than any of the solvents tested. We prefer fifth-normal nitric acid to the other solvents. lt dis- solves the calrzium phosphates in the quantity in which they may occur in soils completely; which may not take place with more dilute solvents. lt has analytical advantages over citric acid, heing much more easily manipulated. E/‘fecl of Ratiopf Solvent t0 PlI()S})‘l!07'l(? Acids-In the results just discussed, 0.2 gm. phosphoric acid was hrought in contact with 1000 e.c_ solvent correspondingto a soil containing 0.2 per cent phosphoric acid. Yery fey’ soils contain near this amount of phos- phoric acid soluble in such weak solvents. For this reason. experi- ments were made using 0.05 gm. and 0.025 gm. phosphoric acid to 1000 c.c. solvent, corresponding to soils containing 500 and 250 parts permillion ot phosphoric acid oi’ the kinds in question, The results of these experiments are prcse-nted in Tahle 3. With fifth-normal nitric acid larger percentages of phosphoric acid were (lissolved when the quantity of phosphoric acid was re- tlticetl, but the increase was not proportional to the reduction. Not over 10 per cent of the phosphoric acid of hasie iron and aluminium phosphates in the soil would be dissolved l)_V this solvent, and proh- ably much less than this percentage. Fiftietlt-iiornza] l23/(l1'0clzl01'ic (icid will dissolve nearly all the phosphorite, apatite, or calcium phosphate contained in the soil _15__ when the phosphoric acid in these minerals does not exceed 250 parts per million, Its solvent power for the iron and aluminium ‘phosphates is much less, though it rlissolve-s nearly all the triplite presented t0 it when containing less than 250 parts per millio-n phosphoric acid. It appears probable than N / 50 hydrochloric acid will distinguish more sharply between calcium phosphates and iron and aluminium phosphates than N/S nitric acid, but at the same time there is danger that all the calcium phosphates may not be " dissolved, and this is almost certain to be the case if more than 250 I parts phosphoric acid per millio-n is present in these forms. Two-hundredth-normal hydrochloric acid does not dissolve any g of the minerals completely even when only 250 parts per million phosphoric acid is present. For this reason we consider it to be i‘ an unsatisfactory solvent. TABLE 3. Effect oi Ratio oi Solvent to Mineral in Percentage oi Phosphoric Acid Dissolved. N /5 Nitric N/5 Hydrochloric N/ 200 Hydrochloric Acfd. Add. Ac d. Grams of Phosphoric Acid to 1,000 . . . . . . . . . . . . . . . . . . 0.200 025 0 200 .050 025 0 200 05 025 45 Apatite, CaaPgOa +Ca(ClF),—- per- ‘ olved . . . . . . . . . . . . . . . 100 . . . . . . . . . . . . 70 3 73.5 . . . . . . 31 2 45 3 . . . . . . . . . . . . . . . . . . . . .. . 100 470........ 97.1 158...... 608 ‘ . . . . . . . . . . . . . . . . . 100 . . . . . . . . . . . . . . . . . . . . 100.0 . . . . . . . . . . . . 92 9 Phosphorite, CaQPQOB +4H,O 100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9) 4 l0 Vflrispite, AlPO4+2H,O. .. ... ....-. . . . . . . . .. 12.8 . . . . . . . . . . .. 113 Wavellite, AlP4O19+12H2 g g) 4.8 . . . . . . . . 5.3 2 4 . . . . . . 5 2 _ - Ferric Phosphate . . . . . . . . . . . . . . . . . . . . . . . . ._ 16.0 34 5 37.3 8.5 28 3 25.1 7.1 Vivianite, Fe3P203+H2O . . . . . . 97 8 . . . . . . 36.0 39 5 37.2 28.0 23 3 21.9 j 1 “ . . . . . . . . . . . . . . . . . . . . . . 93.0 . . . . . . . . . . . . . . . . . . . . 70.7 . . . . . . . . . . . . 44.0 f “ . . . . . . . . . . . . . . . . . . . . . . 91.0 . . . . . . . . . . . . . . . . . . . . 41.1 . . . . . . . . . . . . 28.9 Triplite, (FeMn),P,OB+(FeMn) F2. 99.5 . . . . . . 41.2 70.5 83.9 . . . . . . 29.3 30.9 " . . . . . . . . . . . . . . . . . . . . . . . . 0.7.0 . . . . . . . . . . . . . . . . . . . . 93.3 . . . . . . . . . . . . 70.0 p; f‘ . . . . . . . . . . . . . . . . . . . . . . . . 82.0 . . . . . . . . . . . . . . . . . . . . 93.1 . . . . . . . . . . . . 00.3 ;. Dufrenite, Fe4P2O,'3H,O . . . . . . . . . 4.8 6 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. J “ . . . . . . . . . . . . . . . . . . . . . . 8.0 9 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ifiect 0f 1incrca.s'i.ng Strength 0f S0Zvent.-—The analyses of a few tions made with varying' strength of solvent are present-ed in le 16. Increasing the strength of solvent does not correspond- ‘y increase the quantity dissolved. In many of the soils, the lent eftect of the stronger acid is not much greater than that of iveaker. FIXATION or DISSOLVED PHOSPHORIC ACID, ‘ the preceding section, it was shown that the phosphates of iand aluminium arc only slightly dissolved by N/ 5 nitric acid, the phosphates of calcium are completely dissolved, It a} _16_ should next be ascertained whether the phosphoric acid which en- ters into solution is remo-ved with the solvent, or whether a portion of it is taken from solution by the fixing materials of the soil. In order to study this matter, we treated 200 grams of each soil with 200 c.c. of the solvent to be tested, One of these portions re- ceived a known quantity of phosphoric acid in the form of potas- sium phosphate. If no fixation takes place, the quantity of phos- phoric acid recovered should be equal to that added, plus that dis- solved from the soil. The difference between this quantity and the amount actually extracted represents the amount fixed. The quan- tities of phosphoric acid used were such as might often be dissolved from the soil. Fixation was found to occur with practically all soils. TABLE 4. Phosphoric Acid Absorbed by Soil. Parts per million of phos- phoric acid. 5' b: B .3 ~——- ———*— E g N/ 5 1 8N ,8 z With Nitric Nitric ,3‘ water Acid. Acid 832 Extract from soil plus phosphoric acid . . . . - - . . - - - - - - - - - < - - . . - - - - - - - - 26-0 48-0 101-0 Extract from soil alone . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 8.5 12.5 Recovered from soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.7 39.5 88.5 Addfidphosphoric acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194.0 194.0 194.0 Absorbed (parts per million) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170.3 154.5 105.5 Table 4 shows the results of an experiment with water, N/5 nitric acid and 1.8 normal nitric acid, on a soil known to have a high fixing power for phosphoric acid, and shows the method of calculation we used. The so-il fixed nearly as much phosphoric acid from the N/ 5 nitric acid as it did from the water. The fixation is less with 1.8 normal nitric acid, "but it is 50 per cent of the added phosphoric acid, showing that even with strong acids a very large amount of phosphoric acid may be fixed, Table 5 contains the results of a number of experiments. The ratio of soil to solvent in each case was 1 :10—time, five hours. temperature, 40° C. The absorption ranges from 5 per cent of the added phosphoric acid in the first soil to 94 per cent in the last one. ‘The soils are arranged in the order of their absorptive power from N/ 5 nitric acid solution. The absorption from water is greater than from N/5 nitric acid. Where the absorption from water is less than 50 per cent of the phosphoric acid added, the absorption from nitric acid is about one- half as much as from water. The difierences are not great where over '75 per cent of the added phosphoric acid is absorbed, the fixa- tion in the nitric acid solution being somewhat less than from xvatcr. We may conclude from these experiments that the phos- phoric acid eartracted from the soil by a solvent does not vwcessarily Mia-resent that rrlzich goes into solution. TABLE 5. Absorption 0t Phosphoric Acid from Soils and. Composition of Soils. Percentages of phosphoric Composition of acid absorbed from 200 parts soil. per million addfid- >- ,_ ___ 8.3 _ _ g g N_/5 I\ l2 Acid _ 4oz Water. Nitric Nitric Nitric con- Lime. MgO. Fe2O3 ,3 Acid. Acid, Acid. sumed +Al2O3 176 Norfolk fine sandy loam, Anderson Co. . . . . . . . . . 5 . . . . . . . . . . . . 0 .04 .05 1.42 314 Norfolk fine sand. Houston C0 . . . . . . . . . . . 16 7 0 . . . . . . . . . . . . .10 .0; 1.25 179 Norfolk fine sand, Anderson Co . . . . . . . . . . . . . . . . . 7.5 . . . . . . . . . . . . A . . . . . . .06 .07 1.07 125 Orangehurg fine sandy loam, Lamar Co. 41 14 . . . . . 8 . . . . . . .06 .07 1.62 340 Susquehanna fine sandy loam, Rusk Co. . 33 17 _ . . . . . 17 . . . . . . .06 .11 2.08 821 Orangeburg fine sand, Robertson C0 . . . . . . 38 20 . . . . . . 18 2 4 .17 .1C 3.08 852 Rice soil from Orange, Texas . . . . . . . . . . . . . . . . . . . 20 . . . . . . . . . . . . . . . . . . .38 .32 5.05 896 Norfolk fine sandy loam, Angelina C0.. . . . 46.3 25 . . . . . . . . . . . . . . . . . . .09 .03 2.18 180 Orangeburg fine sandy loam, Anderson Co. . . . . . . 27 . . . . . . . . . . . . 0 .02 .04 0.52 178 Orangeburg clay, Anderson Co . . . . . . . . . . . . . . . . . 32 . . . . . . . . . . . . 10 .23 .22 8.30 103 Houston Clay, Lamar ()0 . . . . . . . . . . . . . . . . . . . . . . 35 . . . . . . . . . . . . . . . . . . .35 .32 4.43 825 Lufkin fine sandy loam, Delta Co.. .. . . . . . 75 68 . . . . . . . . . . . . 5.0 .42 .40 11.52 332 Houston Clay, Hays C0 . . . . . . . . . . . . . . . . . 8O 70 66 . . . . . . . . . . . . 19.32 .44 12.17 336 Susquehanna fine sand, Caldwell Co... . . . . 85 75 60 51 . . . . . . .70 .20 15.12 832 Orangeburg clay, Robertson Co . . . . . . . . . . 85 77 . . . . . . 53 5.5 0.16 .31 12.81 330 Crawford stony clay, Hays Co... .. . . . . . . . 77 83 . . . . . . 60 . . . . . . 12.40 .30 16.10 823 Orangeburg fine sandy loam S. S., Rohert- 86 94 . . . . . . 65 . . . . . . .40 .91 29.22 son Co. Relation of ;l.0.S’O7']J'/?.'O7Z to C0flll)08'iit'li0fl.——illll€ percentage of the added phosphoric acid absorbed by the soil is related to its content of oxides of iron and aluminium soluble in strong hydrochloric acid. This is brought out in Talole 5. The soils are arranged in the order of their increasing absorption of phosphoric acid from N/5 nitric acid solution. Their contents of iron and aluminium are approximately in the same order, Soils containing over 10 per cent of iron and aluminium oxide absorb over 50 per cent of the phosphoric acid presented to them in N/ 5 nitric acid solution, The two so-ils containing the largest percentages of oxide of iron and aluminium also possess the highest absorptive power for phosphoric acid. It need not require a large percentage of fixing material in 100 grams of soil to take up 0.02 grams of pho-sphoric acid. One-tenth of one per cent of a highly absorptive material sho-uld sufiice for this purpose. It is, therefore, more surprising that the absorptive pov:er is so closely related to the percentages of oxides of iron and aluminium than that there should be irregularities in these rela- tions. lt would appear that only a small per cent of the oxide of iron and aluminium in the soil has a high fixing power, and that __13_ this percentage is comparatively constant, or else the fixing mate- rial has only a low fixing power. The soils with the highest percentages of lime did not have the highest fixing power, even from aqueous solution. Efiect of Qutmtaity of Phosphoric Acid on Percentage of Fixation in Acid Solut/ioru-Jfable 6 shows the effect of different amounts of phosphoric acid on fixation by the soil. In one soil the percentage of fixation decreased with the quantity added. In the other two soils it was nearly constant. The limit of error in using very small quantities of phosphoric acid is so great that it did not appear ad-A visable to carry this line of work further. In two of the experiments the moist soil was treated with phos- phate, allowed to stand forty-eight hours, and then treated with the solvent. In both cases the fixation was slightly increased by stand- 1ng_ TABLE o. Eflect of Diflerent Amounts o1 Phosphoric Acid on Fixation by Soil. Phosphoric acid added (per million of SOll). D 8 56 _ _____ _____________ i? 1 S; 24 9e l 240 19s 196* uz-i- i —— ' ii:- iii ‘ {Ti —i-i—— ——-~i———- 176 Phosphoric acid fixed, per cent . . . . . . . . . . . . . . . . . . . . . . . 20 11 5 . . . . . . . . . . . . . . . . 178 Phosphoric acid fixed. per cent . . . . . . . . . . . . . . . . . . . . . . 33 36 32 . . . . . . . . . . . . . . . . 180 Phosphoric acid fixed, per cent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 23 30 _ 38 103 Phosphoric acid fixed, per cent . . . . . . . . . . . . . . . . . . . . . . . l . . . . . . . . . . . . . . . . . . . . 35 110 Phosphoric acid fixed, per cent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Absorption by Soil Resitlztes.—’l‘he residues of soils treated with acids have in many cases nearly the same absorptive power for phos- phoric acid as the original soils. The soils tested were treated not only with dilute acids at 40°, but with strong acids in the cold. In each case, the residues were washed thoroughly and dried. Fifty grams were brought in contact with 200 c.c. water containing 20 mg. phosphoric acid (400 parts per million of soil) in the form of potassium phosphate and allowed to stand twenty-four hours, being shaken from time to time. The solution was then filtered and 125 ‘c.c. taken for the estimation of the phosphoric acid. The (Jriginal soil was in all cases treated at the same time and under the same conditions as the residues. The results of these experiments are presented in Table No. T. In some of the experiments the time of contact was five hours (Nos. 326 and 336) and in others 40 mg. phosphoric acid was used (Nos. 821. 8?3 and 895): but these (lifierences are not material to the purposes of the experiments. __19__ TABLE 7. Percentage oi Phosphoric Acid Fixed by Soils and Residues. 2/N 4/N SIN i‘ . o l4 f3 .3 Origina! N_/5 Correct- 1.8}; Hydrp- Correct- Hydrp- H ydro- ‘6 g soil. Nitric ed. Nitric chlorlc ed. chloric chloric E2 Acld- Acld- Acid. Acid. Acid. J 1 2 3 4 5 e 7 s 821 . . . . . . . . . . . . . . . . . . . . . . 19.7 13 8 13.8 19.8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340 . . . . . . . . . . . . . . . . . . . . . . 32.1 19 9 19-9 12.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 . . . . . . . . . . . . . . . . . . . . . . 35.5 17 8 17.8 17.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 . . . . . . . . . . . . . . . . . . . . . . 41.2 . . . . . . . . . . . . . . . . . . . . . . .. 41.6 40.0 441 33 1 308 . . . . . . . . . . . . . . . . . . . . . . 59.3 . . . . . . . . . . . . . . . . . . . . . . . . 64.4 62.0 . . . . . . . . . . . . . . . . 825 . . . . . . . . . . . . . . . . . . . . .. 71.5 714 71.2 73 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326 . . . . . . . . . . . . . . . . . . . . . . 81.8 . . . . . . . . . . . . . . . . . . . . . . . . 56.1 52.5 57.4 50.8 330 . . . . . . . . . . . . . . . . . . . . . . 83.0 . . . . . . . . . . . . . . . . . . . . . . . . 80.6 58.2 76.1 77.3 336 . . . . . . . . . . . . . . . . . . . . . . 88.1 . . . . . . . . . . . . . . . . . . . . . . . . 89.3 85.7 85.7 59.6 823 . . . . . . . . . . . . . . . . . . . . . . 96.0 100 88 99 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fifty grams of soil were compared With 5O ‘grams of residue. We also corrected the results with the N/5 nitric acid and the 2/N hydrochloric acid to the weight of residue which would be left by these solvents. The results are shown in the table. The correc- tion of soil Ne. 823 is not accurate, because the absorption could not be over 100 per cent, and the correction was about 13 per cent. H ence it would be impossible to secure a correction which would not cause the residue to appear to absorb less than the original soil. We find that in the case of the residue from N/5 nitric acid, the residues have a lower absorptive power in three cases, and the same absorptive power in two. When corrected, the absorptive power is lower with soil No. 823, but this correction is not well made, for ~ the reasons already given, While the action of the acid decreases the absorptive power of the soil, the residues still have considerable absorptive power. Considering the 1.8/N nitric acid and the 2/N hydrochloric acid, we find decreased absorption by the residues in five cases, and the same as the untreated soil, or an increase in five. When correction is made to the original weight of residue. we find a decrease in seven cases, and little change in two, One is not cor- rccted. The decrease in one ease is only slight. The correction for soil No. 823 is doubtful. We find, therefore, that while cold strong acids may remove part of the absorptive power of a soil, they may, on the other hand, have little or no effect upon it. This confirms our observation that tixation of phosphoric acid by the soil takes place even in strong acid solution. Carbonate of lime does not appear to be so efiective for fixation as oxides of iron and alumina. Ii’ carbonate of lime fixes any phos- phoric acid, there is sufficient oxides of iron and alumina to take _g()__ up most of this fixed phosphoric acid when it goes into solution when the carbonate of lime is dissolved. This confirms the rela- tion already pointed out laetween the proportion of fixation and the percentages of iron and aluminium. Efiect of Proportion of Phosphoric Acid Upon Fixation front lVater. In these experiments, 50 grams of soil were treated for twenty-four hours with 200 c.c. of the solution. The solution varied in strength from 207 to 3792 parts per million of the dry soil. The results are presented in "Table No. 8. These results are, in most cases, averages of two sets of tests. The percentage of fixation decreases With the quantity of phos- phoric acid, slowly at first and then more rapidly. It is nearly constant when 400 parts per million or less is present. TABLE 8. Percentage or Phosphoric Acid Absorbed by Soil. . . ’ l i‘ - Parts phosphoric acid per 1111111611 6r $611 . . . . . . . . . . .. 207i 41st 948; 1896i 8792 95.2 95.2} 91.5 87.8 68.0 .............................................. . . 61.c 59.5. 86.9 28.1 28.1 .............................................. . . 95.1 915* 72.6 56.4 50.6 .............................................. . . j 94.1 87.97 71.7 68.2 48.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80.4 77.5; 72.2 74.5 Extraction of Absorbed Phosphoric Acid.—The object of this work was to ascertain how tenaciously the fixed phosphoric acid is held. Two hundred grams of soil were digested at 40° C. with 200 c.c. N/5 nitric acid. The nitric acid poured upon one portion of the soil contained 200 parts per million of the soil of phosphoric acid in the form of potassium phosphate. At the end of five hours, the solutions were filtered, 1500 c.c, being taken for the estimation of phosphoric acid and silica. The filtrate was measured and its vol- ume recorded. The soil on the filter paper was Washed back into the bottle with 2000 c.c. N/5 nitric acid, and again digested. Four treatments in all were made with the acid The quantity of phosphoric acid found was corrected for the quantity left in the soil and filter paper by the preceding extraction. The results are presented in Table 9. Eight soils were examined. The amount of phosphoric acid re- covered by the first extraction varied from 5 to 87 per cent, and the total amount recovered by four or six extractions varied from 6.2 per cent to 100 per cent. The quantity of phosphoric acid, as a rule, decreased regularly with each extraction, until it became constant at about the same quantity as the original soil. The effect TABLE 9. Extraction ot Absorbed Phosphoric Acid. ‘g2 lst ex- 2nd ex- 3rd ex- 4th ex- 5th ex- 6th ex- fi Q traction traction traction traction traction traction Total i-i 8 821 Extracted from original soil, parts per million . . . . . . . . . . . . . . . . . . . 7.3 7.3 7.0 5.6 . . . . . . . . . . . . . . . . 27.2 Extracted from soil plus 201.3 parts P205 per 1111111011 . . . . . . . . 165.3 17.0 14.6 9.6 . . . . . . . . . . . . . . . . 206.5 Percentage recovered of remaining phosphoric acid . . . . . . . . . . . . . . '79 27 29 22 . . . . . . . . . . . . . . . . 89 823 Extracted from original soil... . . . 6.0 4.7 517 6.5 . . . . . . . . . . . . . . . . 22.9 Extracted from soil plus 201.3 parts per million of phosphoric acid . . . . . . . . . . . . . . . . . . . . . . . . . 17.7 5.5 8.0 5.6 . . . _ . . . . . . . . . . . . 35.4 Percentage recovered . . . . . . . . . . . . 5 0.4 1.0 . . . . . . . . . . . . . . . . . . . . . . . . 6.2 832 Extracted from original soil... . . . 76.0 18.4 17.3 14.3 12.1 11.3 . . . . . . . . Extracted from soil plus 197 .5 per v million of P205 . . . . . . . . . . . . . . 136.5 19.2 18.4 13.1 10.1 11.7 . . . . . . . . Percentage recovered . . . . . . . . . . . . 31 1 1 -1 -1 . . . . . . . . 31 852 Extracted from original soil . . . . . . 19.0 10.8 11.0 8.1 . . . . . . . . . . . . . . . 48.9 Extracted from soil plus 201.3 parts per million P205 . . . . . . . 161.7 55.8 20.5 11.8 . . . . . . . . . . . . . . . . 229.8 Percentage recovered . . . . . . . . . . . . 71 44 30 17 . . . . . . . . . . . . . . . . 90 1590 Extract-ed from original soil... . . . 10.3 5.8 5.9 5.2 8.5 6.0 . . . . . . . . Extracted from soil plus 197.5 per ' million P205 . . . . . . . . . . . . . . . . . 171.3 26 18.2 12.5 12.0 13.0 . . . . . . _ . Percentage recovered . . . . . . . . . . . . 81 56 77 . . . . . . . . . . . . . . . . . . . . . . . . 100 1592 Extracted from original soil . . . . . . 36.3 10.5 4.8 4.5 4.8 5.3 . . . . . . . . _ Extracted from soil plus 197 .5 per million P205 . . . . . . . . . . . . . . . . . 208 0.7 10.0 10.2 4.1 5.1 . . . . . . . . Percentage recovered . . . . . . . . . . . . 87 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 1121 Extracted from original soil . . . . . . 8.3 6.9 6.8 6.4 7.5 l 7.1 . . . . . . . . Extracted from soil plus 197.5 per . million P205 . . . . . . . . . . . . . . . . . 120.3 21.5 16.7 13.7 11.5 10.5 . . . . . . . . Percentagehecovered . . . . . . . . . . . 56 17 14 12 8 7 76 1124 Extracted from original soil . . . . . . 10.7 9.5 9.8 7.0 9.1 7.1 . . . . . . . . Extracted from soil plus 197.5 per million P20, . . . . . . . . . . . . . . . . . 136.7 22.6 20.4 14.3 10.4 10.5 . . . . . . . . D5 V... Percdntage recovered . . . . . . . . . . . . 64 17 18 15 3 8 82 of the added phosphoric acid was usually evident in the fourth ex- traction, and sometimes in the sixth, ~ With a soil of very high absorptive power (No. 832) the added phosphoric acid had no effect beyond the first extraction, and only 6.2 per cent of _tlie added phosphoric acid was recovered in four extractions. 'l‘hcse observations may be applied to the original soils here studied. Soil No. 821 gives practically the same amounts of phos- phoric acid in the first three extractions. As this soil has a low fixing power, we should be justifietl in saying that it contains prac- tically no phosphoric acid easily soluble in N/5 nitric acid (cal- cium phosphate), but all its phosphoric acid is in difficultly soluble forms, of which a. portion i.s given to the acid. Soil No. 821 contains some calcium phosphate, though the quan- tity is not large. I should judge that the amount present is about 2] parts per million of phosphoric acid. . Soil No. 823 probably contains all its phosphoric acid in diffi- cultly soluble forms. It may, however, contain as much as 50 to '75 parts per million of calcium phosphate, Whose presence is masked by the high fixing power of the soil. We judge, however, that all the phosphoric acid of this soil is present in very diflicultly soluble forms. TABLE 10. Eflect oi Proportion o! Soiljto Solvent in fixation. | 0' E z 400 200 100 .8 :- grams grams grams G! A S 823 Milligrams phosphoric acid in 1500 c.c. of solution, without phosphoric acid 1.15 1.4 1.2 with phosphoric acid 2.18 4.15 10.55 Parts per million phosphoric acid without phosphoric acid . . . . . . . . . . . . . 3.83 9.33 16 with phosphoric acid . . . . . . . . . . . . . . . . 197 197 197 Total present . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 8 206.3 213 Found . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3 27.7 140.6 Absorbed .............................. .. . ................... . . 193.5 179.6 12.4 Per cent absorbed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 36 A soil containing] phosphates easily soluble in N/5 nitric acid ivilZ yifeld decreasing amounts of phosphoric acid when subjected to successive extractions. The rapidity of the decrease depends upon the fixing power of the soil. Soils containnzg little or no phosphates of h/lgh solubility, give practically the same amounts 0f phosphoric acid t0 svzccessive eaJtracticns. Soils of very high fixing power may give nearly equal amounts of phosphoric acid to successive extrac- tions, whether they contain easily-soluble phosphates or not, pro- vided these phosphates are not present in excessive quantities. We shall refer further to this work in discussing the SUCCQSSlVQ extrac- tion of natural soils with acids. (See page 23.) Efiect of Ratio of Soil t0 Solvent on Fixation.—This experi- ment was carried out on soil No. 823, which has high fixing powers. Four hundred, 200 and 100 grams soil were brought in contact lVllll 2000 c.c. N/5 nitric acid five hours at 40°. One portion of each sample received 4-0 mg, (approximately) of phosphoric acid. The results are presented in Table 10. The percentage of fixation decreased decidedly when the quantity of soil was reduced from 200 to 100 grams. REILATION OF FIXING POW/ER OF SOIL TO ABSORPTION FROM FIFTH- NORMAL NITRIC ACID. By the fixing power of a soil we here mean its power to absorb phosphoric acid from aqueous solution. The method adopted at this Experiment Station for the work on soils is as follows: Fixing Power of S0iZs.——Bring 50 grams of the soil in contact with 200 c.c. of a solution containing 20 mg. P205 (in the form of potassium phosphate). Shake every half hour during the Working day, filter at the end of twenty-four hours, measure off 125 c.c., acidify with nitric acid, and evaporate to about 5O c.c. Run five soils and one blank on the solution together. Divide the phosphoric acid found by the quantity added and subtract- from 100. Report percentage of phosphoric acid recovered. In this method, the phosphoric acid offered to the soil is 400 parts per million. For the purposes of this bulletin we define the “fixing power” of a soil as the percentage of 400 parts per million phosphoric acid absorbed under the condition described. lt is important to know whether there is any relation between the fixation of phosphoric acid as determined in this way and the absorption of phosphoric acid from fifth-normal nitric acid solu- tion. If such a relation exists, the estimation of the fixing power of a soil will aid in the interpretation of analyses made with fifth- normal acid. The results of a number of experiments are presented in Table 1]. The soils are divided into three groups. Group 1 includes soils whose fixing power is less than 5O per cent. 7We consider these to have a low fixing power, Group 2 includes soils of moderate fixing power, from 5O to 8O per cent. Group 3 includes soils of high fix- ing power, from 80 to 100 per cent. The fixation from acid is, as a rule, lower than from Water. The relation is variable. The maximum percentage of fixation from acid in Group 1 is 27.7 per cent. While the decrease caused b_v fixation in the amount of phosphoric acid dissolved from soils of this group is of some sig- nificance, )iet_v\*e do not consider it of high importance. If we assume that the fixation from acid is 50 per cent of that from water with these soils, we should have a fair aid to our interpretation of soil analyses. The fixation may, indeed, be as much from acid solu- tion as from aqueous solution, but the average would be of assist- ance. The maximum fixation in Group 2 is '70 per cent, but this is an exceptional soil. The next highest is 41 per cent. Here, the matter of fixation, though of greater importance than in Group 1, and not to be disregarded, is not of prime importance. We can __yg4_ again assume that the fixation from acid is one-half the fixation from water, or rather one-half the fixing power, TABLE 11. Fixation from Water and from Acid. Percentage from Soi No. Water Acid 400 200 GROUP 1:— 1592 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . _ . 2.6 1.5 174 . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 7.5 176 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.2 5 314 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.2 7 S96 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.1 20 180 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . , . . . . . . . . . . . 22.5 17.5 340 . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . _ 25.0 17 1135 . . . . . . . . . . . . . . . . . . , . . , . . . . , . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . 28.0 17.5 125 . . . . . . . . . . . . , . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.0 14 1586 . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . , . . _ . . . . . . . . . . . . . . . . . . . , . . . . . 33.1 11 821 . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . 44.8 20 .8 1139 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . 45.5 25 Group 1, average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . 24.4 13.7 GROUP 2:— 52.0 25.7 52.0 26 55.8 32.0 59.5 21.3 60 20 71 35.5 72.8 27 74.6 16.7 75.4 29.6 75.4 37.5 78 39 78 41.4 67.0 29.3 81.7 31.2 83.1 70 83.7 35.5 84.1 18.5 85.1 30.5 85.2 73 80.1 75 86.7 83 87.1 73 88.9 68 94.4 57.1 98.2 94 Group 3, average . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87.0 59.1 I11 Group 3 the fixation from acid varies from 31 td 94 per cent. Six of the soils fix more than 50 per cent of the phosphoric acid, five of them less than 5O per cent. We consider this fixation a matter of great importance in this group of soils. On account of the Wide difference between fixation from xvater and acid no assump- tion can be made as regards the relation between fixation power and fixation from acid, but direct estimations from acid must be made, with approximately the amounts of phosphoric acid supposed to be present in the soil. __2 5__ We believe that the determination of the fixing power of a soil for phosphoric acid should always be made in connection with esti- mation of active phosphoric acid. A Importance 0f Absorption for Soil AnarZg/sisr-We have seen that the extract of a soil with solvents does not represent the solubility of the phosphatic minerals in question, but represents a condition of equilibrium between the solution-tendency and the fixation- tendency of the soil. If highly soluble phosphates are present in a soil of moderate fixing power, the soil extract will contain less phosphoric acid than is really dissolved, but the amount going into solution will still be greater than the solution-tendency of the fixing materials. The extent of the difference xvill depend upon the amount dissolved. The phosphoric acid Withdrawn from solution will be partly given up again when the soil residue is again treated with the solvent, and the amount going into solution xvith successive extraction will decrease until it reaches the solubility of the fixed phosphates, when it may remain constant for some time. A soil of high fixing power may contain a moderate amount of highly-soluble phosphates and yet give no more phosphoric acid to the solvent than if it contained only insoluble soil phosphates. Two soils of this character might be widely difierent in their con- tent of soluble phosphates, and yet give the same, or nearly the same results to a given solvent. It is evident that in the analysis of a soil with a weak solvent, we must consider not only the composition of the soil extract, but also the fixing power of the soil, Only by means of these two factors considered together can we gain any idea of the condition of solu- bility of phosphates in the soil. We will discuss this in detail on a later page, where a discussionof the interpretation of soil anal- yses is taken up. SUOCESSIVE EXTRACTION OF NATURAL SOILS. A number of. soils were subjected to successive extractions in the manner previously described (see page 20). The results of this work are presented in Table 12. _g6__ TABLE 12. - Phosphoric Acid Extracted from Soils by N15 Nitric Acid in Parts per Million. a Extraction No. 8 3-1 i '8 —"_ “k T '8 g 1 2 3 4 32 831 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . , . . . . . . . . . . , . . . . . . . . . 397 90 47 25 928 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , , . . , . . . . . . . . . . . 271 55 86 34 934 . . . . . . . . . . . . i . . . . . . . . . . . . . . . . . . . . . . . . , . , . . . . . . . . . . . . . . . 244 86 40 21 938 . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . , . , , . . . . . . V . . . . . . . . . 258 246 246 288 182 . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . 132 159 97 74 316 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , , . . , . . . . . A 32 6.5 6.5 6.7 821 . . . . . . . . . . . . . . . . V . . . . . . . . . . . . . . . . . . . . . . , . _ , . , . , . . , . . . . . 8 7 6.5 6.0 823 . , . . . . . . . . . . . . . . . . . . . . , . . . . , . . . . . . . . . . . . . . . . . . . . . . . . , . . 5 6.5 5.5 6.1 S52 . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 11 9.8 7.3 896 . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . 30 7.7 7.8 7.0 The phosphoric acid removed falls off rapidly with successive extractions, and shows a tendency to become constant at about seven parts per million of soil. Soil No. 938 gives nearly constant quan- tities of phosphoric acid, but this fact is explained when we con- sider the acid consumed in the successive digestion: Acid Consumed, Per Cent. Digestion No. 1 . . . . . . . . . . . . . . . . . . . . . . . . . .. 99.5 Digestion No. 2 . . . . . . . . . . . . . . . . . . . . . . . . . .. 99.5 Digestion No. 3 . . . . . . . . . . . . . . . . . . . . . . . . . .. 90.5 Digestion No, 4 . . . . . . . . . . . . . . . . . . . . . . . . . .. 44.5 The constant amount of phosphoric acid is thus given up by the solution of a constant amount of lime. The phosphoric acid dis- solved by successive extractions from soils containing moderate amounts of phosphoric acid, closely resembles that dissolved from the fixed phosphoric acid (see Table 9). The curves made by plotting the results are very similar. (See Fig. 1.) It was pointed out by Hall and Amos that the phosphoric acid extracted from the fertilized plots at Rothamsted by successive ex- tractions with citric acid, when plotted, forms a logarithmic curve. Only the plots which had been continually receiving the same super- phosphate manure show this logarithmic rate of decrement in the amounts of phosphoric acid going into solution. They add, “It can hardly be doubted, however, that the logarithmic portions ot the curves represent a single phosphoric acid compound in the soil, which has lacen almost wholly removed after the third extraction, and that the non-logarithmic character of the curves yielded by the other soils indicates that their phosphoric acid is present in a more varied and irregular state of combination, as, indeed, would be ex- pected fro-m the treatment or the history of the plots.” (Hall and Amos, Transactions of the Chemical Society, 1906, p, 215.) 90 00 l00 /\/0. 938 /\/0.3/6 /\/0_ G56 /\/0. 52/ 2 j’ 4 EXTRACT/ON NUMBER Phosphoxic Acid by Nitric Acid (No. 821 and No. 852 with added Phosphoric Acid) ._g3_ L75 /.5 A25 LOGAR/THM .\ Q Q U» 0.5 0B5 \ 2 5 Ex TRA c T/0/v NUMBER Fig. 2.“ Logarithms of Phosphoric Acid extracted by % Nitric Acid. .12 9__ The curves yielded by a number of our natural soils are logarith- mic curves, as shown by Fig. 1 and 2. Soils 821 and 852 do not represent natural soils, but are soils which received an addition 0t potassium phosphate, A It will be observed that the curves of the natural soils are similar to the curve of the natural soil plus potassium phosphate. This po-ints to the truth of the statement of Hall and Amos referred to above, namely’, that the logarithmic curve indicates the presence of a more easily soluble phosphate. Our experiments go to show, however, that this phosphate is not completely extracted by the first three extractions, but its ettects may persist for six or more extractions. Our experiments also make clear the cause of the logarithmic character of the curve it is due, namely, to the fixing properties of the soil. This fixing power varies with different soils, and will influence the amount of phosphoric acid extracted by successive treatments, and hence the exact nature of the curve. Not all the curves shown in Fig. 1 approach the nature of loga- rithmic curves. Soil No. 938 presents nearly a straight line. We have already explained these results as due to the quantity of car- bonate of lime present-—enough to neutralize the acid in the first three extractions. Soil No. 316 represents a common type of curve, in which only a small quantity of soluble phosphoric acid is present, and the amount extracted is nearly constant after the first extraction. A number of soils would give a similar curve (see Table 14). The cause of the deviations of No, 928 is not known. We may consider it established that soils contain phosphates of high solubility in N/fi nitric acid, and phosphates of low solubility; that the fixing power of the soil prevents all the highly-soluble phosphoric acid appearing in the extracts. but causes a decreasing quantity of phosphoric acid to be present in successive extractions; that after a number ot extractions the quantity of phosphoric acid extracted tends to become constant. It would appear that this con- stant quantity should be about '7 parts per million, though this quantity was not reached in all our extractions. TABLE 13. Extraction With Various Strengths of Acid. (Phosphoric Acid in Parts per Million.) Extraction No. 1 2 3 4 l 5 6 Soil No. 831—N/ 2 Nitric Acid . . . . . . . . . . . . . . . . 569 121 39.6 29.3 22.6 19.6 2 cid . . . . . . . . . . . . . . . . . . . . . . . 646 117 33.6 32.5 23.0 25.3 Soil N0. 928-} N. Acid . . . . . . . . . . . . . . . . . . . . . . . 1427 123 55.0 34.7l 29.0 20.2 2 Acid . . . . . . . . . . . . . . . . . . . . . . . 1527 214 51.6 38.7 25.3 24.6 Soi ——N/ 2 N Acid . . . . . . . . . . . . . . . _ . . . . . . . . . . . . 909 269.6 65.6 23.6 21.0 15.3 2N Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . 896 120 25 28.3 19.1 21.0 __3()__ Successive Extraction with Strong Ac'ids.——'l‘able 13 chews the results of extraction with two strengths of nitric acid. The results are similar to those secured with N/5 nitric acid. Somewhat more phosphoric acid is se-cured by the stronger acid with the first ex- traction, but the results of the succeeding extractions are very close together. . ‘ Table 14. Eflect ot Strength of Solvent on Extraction 0t Phosphoric Acid >a §t' N/5 N/2 1,81; E ‘a’ W ater Nitric Nitric Nitric ,8 s Acid Acid Acid .32 _ ........................................ .. 13 34 i%§11:;:i::1:;;ji ........................................ ‘i 8 ...... .. 22 g9 . . . x . , . . . . . . . . . . . . . . . . . . . . , . . . . . . . . , . . , . . , . . . . . . i . . , . . .. a :37 .... lll6é 50a asi»lIllflffjIiilIlIIiIjIjIIIfIfIllilffIIjIiIliIiflllIIll 2 5' 5 "" '6' . . . . . . . . . . . . . . . . . . . , . . . . . . . . , . _ . . . . . . . . . . . . . . . . . . . . . . .. g 135 25 ...... .. s32IIIIIQIIIIL"1111111111I1I11I1'.flllllilllilllllilllLIII 2.3. sI5.fII'.l1'.""'1'2'.5 s21 . . . . . . . . _ . , . . . . . . . . . . i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 .65 ...... .. 23.0 s23 . . . . . . . , . . . . . , . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 10.5 ...... .. 43.5 s95 . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. t 3.5 19.5 ...... . 4 46.5 EFFECT OF STRENGTH OF SOLVENT. Table 14 shows the phosphoric acid secured by extraction with water, N/ 5 nitric acid, and. other solvents. The amount of phos- phoric acid increases with the strength of the solvent. The addi- tional phosphoric acid secured by the stronger acid comes from the more insoluble phosphates, and not from the easily soluble phos- phates, EFFECT OF SULPHATF. OF LIME. The effect of sulphate of lime upon several soils was studied. Soils were selected which are high in iron, as it was found in pre- vious work by the writer (Amer. Chem, Journal 23, 1, 1901) that sulphate of lime increased the amount of phosphoric acid which went into solution and also increased the amount of iro-n dissolved. In these experiments, one gram of sulphate of lime was added to 100 grams soil and the soil extracted with N/ 5 nitric acid. At the same time, an extraction was made without the sulphate of lime. (See Table 15.) The soils, in all cases, gave darker solutions when treated with sulphate of lime, indicating a larger solution of iron. The results of the experiments show that the sulphate of lime in- creases the solvent action of the nitric acid, both for iron and for phosphoric acid. The difference is probably due to the increased solubility of the basic phosphates of iron. We do not attach any great importance to this matter, for very few soils contain appre- ciable amounts of sulphate of lime, TABLE 15. Eflect oi Sulphate oi Lime Upon Phosphoric Acid Dissolved by N/15 Nitric Acid. (Phosphoric Acid in Parts per Million.) Sul hate of ime added- Ne addition. Laboratory Number. u-n P‘ b3 ~1 r-n-n-ntzlwfl PPWIQWL» Cwwn-AMUH-l [OQ §$wr?@ WOJOIOWO The only significant point is, whether the addition of sulphate of lime would make phosphoric acid available, The sulphate of lime increased the dissolving action of the nitric acid, but this is no evidence that it has changed the form of combination of the phosphates, or that it would increase the solvent action of the roots upon such phosphates. SOLUBILITY OF CONSTITUENTS OF THE SOIL. The solubility of the constituents of the soil must be considered as a factor in the analysis of soils with weak solvents. If any quantity of the soil passes into solution, phosphates will be exposed to the action of the solvent which were protected from the action of soil moisture and roots, and which are really physically unavailable. This factor must be, given careful consideration For example, N/5 nitric acid dissolves 320 parts per million of lime (CaO) from soil No. 1'76, while from soil No. 938 it dissolved 53,250 parts, which corresponds to nearly 10 per cent carbonate of lime. The amount of phosphoric acid brought into action through the solution of the lime in the soil first named may not be large, but in the case of the second soil, 10 per cent of the soil enters into solution, and all the phosphoric acid protected within this 10 per cent is exposed to the action of. the solvent. This action is further emphasized, in the ease of the soil just mentioned, by the fact that a second treat- ment with acid dissolves 43,400 parts per million of lime addi- tional, and a third treatment dissolves 46,360 parts, making a total of about 14 per cent of lime dissolved from the soil, corresponding to about 25 per cent carbonate of lime. This soil, of course, represents an extreme instance, but it em- phasizes the difference between a calcareous and a non-calcareous soil. In a non-calcareous soil, the phosphoric acid inclosed within the soil particles is protected from the solvent, while in a cal- __3g-_ careous soil, that portion of the phosphates included in the cal- careous matter dissolved by the acid is exposed, and may be dis-_ solved. Since the phosphoric acid dissolved from a non-calcareous soil is present on the external surface of the soil grains, and accessible t0 the roots of the plants and the action of soil moisture, while that dissolved from calcareous soils is without doubt, in part included within the soil grains, and not accessible to plant roots, it is obvious that calcareous soils may contain a larger quantity of active plant food than non-calcareous soils, and yet require fertilization with phosphates on account of the phosphoric acids being protected. Two calcareous soils may also contain the same amount of active plant food, and yet differ in the amount plants can take from them. In one the phosphates may be on the extreme surface of the soil grains, in the other it may be disseminated through them. Calcareous soils are more durable than non-calcareous soils, This may be explained by the fact that the gradual weathering of such soils continually exposes fresh surfaces of phosphatic minerals. There are other cause-s for this fact, however. - "Acid Uonsumedfi-‘The acid consumed in digesting a soil with N/ 5 nitric acid (or with other acids) may be easily determined, and may serve as an approximate measure of the quantity of lime and magnesia which enters into solution. Our custom has been to express the amount of acid consumed in percentage of that used. For example, if 10 c.c. 0-f the acid re- quires 20 c.c. caustic soda to- neutralize it before digestion, and 18 c.c. afterwards, then the acid consumed is 10 per cent. Phenolphtha- lein is used as an indicator, so that the acid consumed corresponds torlime and magnesia, and does not include iron and aluminium. The following table shows the percentages of lime calculated from acid consumed. The ratio of soil to acid is 1 :10, and the acid is N/5. TABLE 1e. Bases Corresponding to Acid Consumed. . P i 1 7 ‘ \ ‘ ' Per cent acid consumed. uqu“ aidiiitsdiirgdrffdrliit (Lao, Lorbiirsylfdiiiditieg citellniieelit of 5 0.28 0.50 10 0.56 1.00 20 1.12 2.00 50 2 80 5.00 100 5 60 10.00 The method for the estimation of the acid consumed is described as follows: Digest 10 gm. soil for five hours at 40° with 100 c.c. Ni/5 nitric acid. Filter. When cold, measure oif 10 c.c., heat to boiling, boil three minutes at least, and titrate with N/10 caustic _33__ soda and phenolphthalein. Make a blank 0n the original nitric acid solution, and calculate the percentage of acid which Was consumed by the soil. This determination is usually made in connection with the esti- mation of the phosphoric acid (and potash) soluble in N/ 5 nitric acid, a portion of the filtrate being used for acid consumed, Importance 0f Acid Consumcd.—'l‘he “acid consumed” is an in- dex of the amount of lime and magnesia dissolved by the nitric acid, and shows the amount of this material through which the phosphoric acid extracted from the soil may have been difiused. For example, take two soils containing 50 parts per million of phosphoric acid. Suppose one consumes 1 per cent of the acid, the other 50 per cent. In the first soil, practically all the phosphoric acid is upon the external surface of the soil grains, and accessible to plants. In the second soil, the 50 parts per million of phos- phoric acid may be distributed through the equivalent of 50,000 parts per million of carbonate of lime. How much of the phos- phoric acid may be exposed to plant roots in the latter case depends upon the manner of distribution of the phosphoric acid and the size of the soil particles. With. the same distribution, the smaller the soil particles, the greater the exposed surface. Percentages DtSSOZ7J€d by “Teal: SOZvcnts.—Table 17 shows the percentages of silica, oxides of iron and alumina, lime and magnesia dissolved from certain soils by N/5 nitric acid. There are con- siderable differences between the various soils. Silica varies from .015 to 0.44 per cent; oxides of iron and alumina from 0.01 to 1.39; lime from .009 to 5.32, and magnesia from 0.016 to 0.19. The acid consumed varies from 0 to 100 per cent. The greatest and most significant variation is with the lime. The silica shown in the table is that actually dissolved by the solvent. That which was set free, bu.t remained undissolved, was not determined. ‘Table 18 shows the quantity of oxides of iron and alumina, lime, and magnesia dissolved by weak solvents expressed in percentages of the quantity dissolved by hydrochloric acid of 1.115 specific gravity (A. O. A. C. methods). It is evident that considerable variation exists between the solu- bility in weak solvents of the constituents of various soils. It is evident that, since the dissolved material may contain, or protect, plant food, which thus is not exposed to the action of roots, a factor "of considerable complexity is introduced into our interpretation 0t the analyses of. soils with weak solvents, It is evident that this factor cannot be disregarded, but must be studied, and valued. _34__ TABLE 17. Percentages Dissolved by N/B Nitric Acid. E‘ p. Oxides ‘$3 Dis- of iron Acid ‘6 E solved and Lime Magnesia con- _Q g . . . s z silica alumina suined 125 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.21 0.11 .69 .018 . . . . . . . . 326 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44 1.39 1.40 .06 . . . . . . . . 336 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . .18 .58 .34 .04 . . . . . . . . 831 . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 .48 2.76 .19 50.4 844 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 .27 .53 .04 9.5 845 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 .33 .51 .21 12.5 923 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25 .60 2.62 .18 27 934 . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 .47 2.59 .13 92.5 938 . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . .06 .11 5.32 .12 99.5 176 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .015 .04 .032 .03 0 178 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .098 .31 .26 .03 10 180 . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .030 .10 .08 .03 0 103 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .084 .46 .26 .016 . . . . . . . . 110 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .12 .42 4.36 .016 . . . . . . .. Maximum . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . 0.44 1.39 5.32 0.18 100 Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.015 .04 0.009 0.016 0 TABLE 18. Material Dissolved by N/5 Nitric Acid in Percentage of that Dissolved by Strong Hydrochloric Acids. g g I Oxides m": of iron _ g g and Lime Magnesia 3 z alumina 125 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 15 25 326 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 89 7 336 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 49. 20 831 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 88 19 . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . g 82 13 . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 42 176 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 8 6 178 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 100 14 180 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 100 40 103 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 74 _ 5 110 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 77 2 Maigiinum . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1O 100 42 Minimum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 8 2 Average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 72 18 Apparently, it is of the greatest importance in connection with calcareous soils. At all events, the difference between calcareous and non-calcareous soils is most marked. But we are not yet ready to state that the differences between the amounts of silicates de- composed, and of iron and alumina dissolved may not be of great importance in comparing different soils. Suppose, for the sake of comparison, we assume that the dissolved material contains 1 per cent of phosphoric acid. Then for each 0.01 per cent dissolved, 1 part per million of phosphoric acid would be exposed to the solvent. Then the phosphoric acid exposed by solution of iron and alumina in the eleven soils studied (Table 1.2) would vary from 4 to 139 parts per million; that exposed by the solution of the lime, from 3 to 532 per million; by the magnesia from 2 to 18. It is thus evident» that the differences might be considerable, and that two soils might expose the same amount of the same kind of phos- phates to the plant roots and yet give up very different. amounts to an acid solvent, or they might expose different amounts, and yet give up nearly the same quantities. It is at present impossible to make any correction for the phos- phoric acid exposed by the solvent action of the soil constituents. 1t is a matter which must be carefully considered in connection with soil analyses. TABLE 19. Material Dissolved by Successive Extractions in Parts per Million. Laboratory number of soil . . . . . . . . . . . . . . . . . . . . . 831 844 845 928 934 938 _ F6203, A1203, P205: First extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 820 2,670 3,370 6,010 4,700 1,060 Second extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5,000 1,3 3,940 3,910 4,880 3,990 Third extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2,940 1,080 2,870 2,750 2,770 4,830 Fourthsxtraction . . . . . . . . . . . . . . . . . . . . . . . . . . . 2, 250 1,010 1,930 2, 050 2,080 2,150 ' Ca : First extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27, 633 5, 318 5,174 26,165 25,924 53, 249 Second extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3,675 663 700 1, 913 3, 29,7 43, 406 Third extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370 218 843 469 1, 063 46,364 Fourfii extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 181 173 181 251 24, 568 a0: First extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1,947 417 2,106 1, 764 1,329 1, 156 Second extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526 170 308 736 580 1,000 Third extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 199 431 427 319 315 Fourth extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 178 174 348 279 544 Efiect 0f iguccessive Extractions.——The amounts of material dis- solved by successive extractions with N/ 5 nitric acid is shown in Table 19. It is evident that the quantity dissolved by the second extract-ion may be large, and may continue large for several succes- sive extractions, That is to say, new protecting material may be removed and expose new quantities of phosphoric acid to the dis- solving medium. This is especially the case it the acid is nearly or completely neutralized during the previous extraction. In such event a large amount of lime may enter into the second extract. All the material dissolved is less in subsequent extractions. The decrease is more rapid when large quantities are dissolved by the first extraction. There appears a tendency towards constancy, the silica at about 500 parts per million, the iron and alumina at 2000( '5’), the lime at 200, and the magnesia. at about the same. This statement applies only to the soils studied (see the table). The silica and oxides of iron and alumina fall off slowly to about one-third in the fourth extraction. The amounts of lime and mag- nesia extracted decrease rapidly. Such would not be the case with soils containing less soluble calcium salts. Table 20 shows the quantity of material removed from two soils I __3 6__ by successive extraction with N/2 and 2 N nitric acid. The dif- ferences between the amount of material extract-ed by the two solvents are not as great as one would expect, There is exhibited the same tendency that was observed with the weaker solvent to- wards a slow falling off in the iron and alumina dissolved, and a rapid falling ott‘ in the quantities of lime and magnesia dissolved. It would appear that lime and magnesia are present in the soil (a) as highly soluble compounds, such as carbonates; (b) as mod- erately soluble silicates, and (c) silicates of low solubility, The iron and alumina compounds differ in solubility, but much less than the lime compounds. TABLE 2o. Extracted by Successive Digestions with Nitric Acid in Parts per Million. Laboratory number of soil . . . . . . . . . . . . . . . . . . . . 831 928 938 2N N/2 2N N/2 2N N/2 Oxide of iron and alumina: First extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8,390 5,530 9, 290 5,750 5, 240 1,810 Second extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . 5,240 4,130 5,670 4,040 3,090 1,830 Third extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2,880 1,910 3, 160 2, 380 970 1,190 Fourth extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . 3,820 3,340 4,430 3,270 1,640 1, 490 Fifth extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 200 3,260 3,680 3, 190 1,280 1,270 Sixth extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5, 320 3,360 3,520 2,850 1,190 1, 020 Lime: First extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 22,958 22,653 22,699 10,705 119, 478 94,267 Second extraction . . . . . . . . . . . . . . . . . . . . . . . . . .1 . 4, 381 3,605 1, 321 707 44,920 1,072 Third extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576 699 393 452 3,616 914 Fourth extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 325 358 333 349 526 Fifth extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . r 86 185 lost 214 193 218 Sixth extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 185 205 189 181 164 Magnesia: First extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2,196 1, 784 1,714 2, 021 1,199 lost Second extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . 989 351 1,153 554 1,008 601 Third extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728 543 1,012 722 388 406 Fourth extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . 952 355 786 558 202 243 Fifth extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627 446 lost 553 297 254 Sixth extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 029 525 721 742 289] 264 Efitect 0f Concentration of Acid on Soluibilityr-Table 21 shows the effect of different concentrations of nitric acid upon three soils. Other results are given in Table 21. Increasing the concentration of the acid increases the amount dissolved, but not in proportion to the strength of the acid. For instance, making the acid two and one-half times stronger (N/5 to N/2) increased the average amount dissolved about 20 per cent. Increasing it from N/2 to 2N, or four times, made an increase of about 25 per cent in the dissolved material. This is further evidence of the diiierence in the solubility of the compounds of the same. element in the soil. Relartioni 0f Citric to Nitric Acid.-—In order to ascertain what differences exist between citric and nitric acid, the same soils were treated with 1 per cent citric acid and N/5 nitric acid (five hours at 40° C.) and the solution subjected to analysis. There were selected for this experiment soilswhich she-wed differences between _37_ the quantities of phosphoric acid dissolved by the two solvents. (See Table 22.) TABLE 21. Effect of Concentration of Acid on Solubility of Soil Constituent. >i l A Nitric Acid E ‘é don iii-iii‘ iii}??? ‘<5 5 l gz N/5 N/2 i 2N 12s Silica (dissolved) per cent ..................................... .. 0.21 0.32“ 0.49 326 Silica (dissolved) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.44 0.52 0.27 336 Silica (dissolved) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.18 0.24 0.37 Average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.28 0.36 0.30 Per cent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 129 135 125 Oxides of iron and alumina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 0.11 0.18 0.28 326 Oxides of iron and alumina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1.39 1.43 1.75 336 Oxides of iron and alumina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ._ . . . . . . 0.58 0.81 1.17 Average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.69 0.81 1.07 V Per cent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 I17 154 125 Lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . .009 .010 .008 326 Lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1.40 1.37 1.65 336 Lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.34 0.41 0.43 Average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.58 0.63 0.70 Per cent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 109 121 125 Magnesia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.018 0.022 0.039 326 Magnesia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 0.06 .085 .092 336 Magnesia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .041 .058 .090 Average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.040 .055 .071 Pei‘ cent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 137 177 -1‘ 125 Phosphoric Acid per million . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 19 26 326 Phosphoric Acid per million . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 500 550 336 Phosphoric Acid per million . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 10 14 The solvent action of citric acid is lower than N/ 5 nitric acid 0n practically all the soils, The differences are apparent both for oxides of iron and alumina, and for magnesia, and all the differ- ences are in the same direction, That is to say, in none of these soils does the citric acid dissolve more than the nitric acid. TABLE 22. Relative Solvent Power of Citric and Nitric Acids. l-l l-l i-l a i-i l-l o; \ 1131301210117 §Sao3i§g=° Number. Oxides of iron _ and alumina Lime Magnesia P205 per million 1% N/5 1% N/5 1% N/5 _ _ N15 Citric HNO 3 Citric HNO 3 Citric HNO 3 Citric HNOs . . . . . . . . . . . . . . . . . . .. 0.14 0.58 0.10 .34 .01 .045........ . . . . . . . . . . . . . . . . . . . . .03 .04 .02 .03 .01 .03 9i 8 . . . . . . . . . . . . . . . . . . . . .09 .31 .22 .26 .02 .03 51 30 . . . . . . . . . . . . . . . . . . . . .04 .10 .06 .08 .02 .03 12 12 . . . . . . . . . . . . . . . . . . . . .14 .46 .11 .26 .02 .016 10 11 . . . . . . . . . . . . . . . . . . . . .09 .43 190i .436 0.02 .016 74 61 . . . . . . . . . . . . . . . . . . . . .07 .12 .01 .01 .01 .07 12 9 Average per cent. . . 0.086 0.29 0.35 0.76 .016 .034 . . . . . . . . . . . . . . . . __3g_ SIGNIFICANCE OF THE PIIOSPI-IORIC ACID DISSOLVED BY DILUTE ACIDS. In the preceding pages the fact has been. established that the phosphoric acid extracted from the soil by N/5 nitric acid (or some other weal: solvent) does not represent the phosphoric acid which goes into solution. lVliat it represents is the condition of equilibrium iaetween the phosphoric acid dissolved, and the fixing power of the soil for phosphoric acid. Further, ‘the phosphoric acid dissolved is no-t alone that upon the surface of the soil grains, but that within such soil particles as are soluble or partly soluble in the solvent. Any interpretation of a soil analysis which leaves out of consideration these three factors, is liable to- be Wrong. Before making an interpretation of the meaning of the phos- phoric acid dissolved from a soil by a weak solvent, it is necessary to have the following information: . (1) The quantity of extracted phosphoric acid. (2) The acid consumed. (3) The fixing‘ power of the soil. Under exceptional conditions it may be necessary to know, in ad- ditio11: ‘ (i) The phosphoric acid extracted by successive extractions. (5) The complete composition of the soil extract. (6) The fixation from the solution of the solvent, bligniyicainrce of the Dissolved PILOSPII/OTIG Aci(Z.—\Vhen 10 or less parts per million of phosphoric acid is present, associated with a fixing power of less than 50 per cent. and ivith acid consumed less than. 90" per cent, it indicates that practically none of the phos- phoric acid of the soil is present as apatite, calcium phosphate. or similar compounds, but must be present as basic phosphates or basic ' aluminium phosphate. IVhen 10 or less parts phosphoric acid are present and the soil has a high fitting power for phosphoric acid ('75 per cent or more), calcium phosphate-s may or may not be present. That is to say, our method can not in this case distinguish between phosphoric acid which goes into solution from calcium phosphate and is then removed by fixation, and that which comes from the basic phos- phates of the soil. The origin of the soil will throw some light upon the matter. If the soil is geologically old, the phosphoric acid has probably all been converted into basic phosphates. If the soil has been recently formed from rocks containing apatite and other pho-sphatic minerals, it is possible that calcium phosphate may still be present. In the majority of soils having a high fixing power and a low content of phosphoric acid, provided that they have not become fertilized. the phosphoric acid is probably present as basic iron and aluminium phosp-hates. I _39__ A soil of high fixing power such as above mentioned would _vield up the same quantity of phosphoric acid to the solvent, whether fertilized or not fertilized, unless a very heavy application of phos- phoric acid has been made. One thousand pounds of 16 per cent acid phosphate would represent an application of 8O parts per mil- lion of phosphoric acid, and this heavy application would not. in- crease very much the phosphoric acid removed from soils of very high fixing power. A soil containing 100 parts per million of phosphoric acid, with a low acid consumed, and with a fixing power of less than 50, probably contains a corresponding amount of calcium phosphate accessible to the roots of plants. A so-il containing 100 parts p-er million of phosphoric acid, with an acid consumed of 2O per cent, may or mav not expose much phosphoric acid to the roots of plants, It is impossible to say how much of it is protected by the calcareous material. It is impossible to distinguish phosphoric acid in its several dif- ferent forms, For example, suppose plots were fertilized with Thomas phosphate, phosphate rock, acid phosphate, and apatite. We could not expect to find a relation between the phosphoric acid dissolved from these plots and the crop production. All these ma- terials would give up their phosphoric acid equally well to the solvent used. RELATION OF POT EXPERIBIEYTS TO THE ACTIVE PHOSPHORIC ACID. For about ‘four years we have been making pot experiments with representative Texas soils from different p=arts of the State. These experiments were carried on under varied conditions. With some of them the conditions were very “favorable, while with other groups the conditions were not so suitable. The results are, therefore, not comparable one with another. We can, however, compare the crops produced on the p-ots receiving phosphoric acid with those without phosphoric acid. From the work presented on the previous pziges, it appears that the phosphoric acid dissolved bv fifthnormal nitric acid from a natural soil, in excess of 9 parts per million. as a rule, comes from the phosphates of lime. There may be soils which contain easilv- soluble non-basic phosphates of iron and aluminum, but we are inclined to believe that such soils are exceptional. It does not follow that soils containing the same quantity of phosphates of lime should react in the same manner towards phos- phatic fertilizers, The phosphates may be different in value in different soils. . The phosphates which are dissolved b_v a solvent may be on the _4()_ outside of soil particles, and exposed to plant roots, or Within the soil particles, as already pointed out, The phosphoric acid dissolved from a soil in excess of 8 parts per million is, in most cases, present as phosphate of lime. But we must make a. distinction between the phosphate which goes into solution and that which is removed in the extract. A portion of the dissolved phosphoric acid is withdrawn from solution by the soil. Reducing it to its lowest terms, the analysis of a soil with N/5 nitric acid amounts to this: Knowing the quantity of phosphoric acid extracted by the solvent, and the absorptive power of the soil for phosphoric acid, we must estimate how much phosphate of lime is present in the soil, Then, knowing the amount of acid consumed, we must judge to what ex- tent this phosphate is distributed within the mass of the dissolved material, and to what extent it is exposed to the roots of the plants. Having estimated the amount of exposed phosphate of lime, we have next to inquire how much of it is necessary to make a soil fertile? What. conditions affect the rate and the quantity of phos-i phoric acid which these phosphates give up? Then we have to con- sider the probable value of the basic ferric and aluminium phos-‘ phates, which are present, and whether 0-r not organic phosphates may not be in the soil. Having considered all these questions we shall be in a position to interpret the analysis of a soil with N/5 nitric acid. l CONDITIONS WHICH AFFECT PRODUCTION IN POTS. In pot experiments, the attempt is made to keep all conditions constant except the one to be tested, maintaining the others as fa- vorable as possible. It is, however, impossible to maintain only one variable. The main variable may be predominant, but there are others to be considered. Suppose, for example, we. are studying the effect of acid phosphate on the soil, as is the case with much of the work here presented, We apply a. complete fertilizer containing phosphoric acid, potash, and nitrogen, and compare its effect with a sample to which potash and nitrogen only are added. The vari- able is thus phosphoric acid. But in addition the phosphoric acid may undoubtedly affect the bacterial life in the soil, and this effect may conceivably be either favorable or unfavorable to the develop- ment of the plant. The effect upon the bacterial life may vary in different soils. The phosphatic fertilizer may also have some effect upon the reaction of the soil, according to the kind of material used, and this may vary from soil to soil. It is quite possible that these secondary reactions may on some soils have greater effect than the primary one, namely, the presence or absence of the phos- phoric acid. It is obvious, however, that some controlling condi- __4c1__ tion must limit the size of the crop in pot experiments, either the season and climatic conditions, the soil, or soil conditions. Sup- pose the conditions are so favorable that the phosphoric acid in the soil and fertilizer, together, becomes the controlling condition. It is obvious that the phosphoric acid of the soil can not alone force as large a production as the fertilized soil, so that the soil must appear deficient. The soil may be an excellent one, and able to yield good crops without fertilizers, but if in our pot experiments other conditions are so favorable that the total and largest amount of phosphoric acid becomes the limiting condition, the soil must appear as deficient no matter how good it is. The crop from the unfertil- ized soil will be large, but that from the fertilized one will be larger. This is, of course, an extreme case. Seasonal conditions and the seed will often limit the crop. Yet it is possible in pot experiments to demand of the soil in the pot more than very fertile soils can accomplish in the field. We shall come back to this subject later. - The conditions under which pot experiments are made are un- doubtedly, in some respects, more favorable to the soil than field conditions, Some of the conditions may also be less favorable. In our work, the soil is Well pulverized, and thus in a good mechanical condition. It is usually air-dry, and it has been shown that air- dried soils are perhaps more productive than the same soil not dried. The soil is subventilated, and this is a distinct advantage, especially for heavy clayey soils, The temperature in the pots is probably higher than the temperature of the soil in the field. The applica- tion of results of pot experiments to field conditions must be made a subject of study. METHOD OF WORK. These pot experiments were not all conducted in exactly the same manner, but the general procedure is as follows: Washed gravel was added in sufficient amounts to an 8-inch Wagner pot to make the total weight 2 kilograms. Five kilograms of soil was then added. The soil had been previously pulverized in a wooden box with a wooden mallet until it would pass a 3 mm. . sieve, gravel being removed. The addition of fertilizer consists of 2% grams of acid phosphate, 1 gram nitrate of soda, and 1 gram sulphate of potash. In later experiments 1 gram of ammonium nitrate was used in place of nitrate of soda, If the size of the crop appeared to render it neces- sary, more nitrate of soda or sulphate of potash was added to the pot. They were added in solution, 10 c.c. equals 1 gram, but if added after planting, the solution was diluted with about 200 c.c. of water. _4g__ The seed were weighed out so that each pot received the same amount of seed within 0.1 of a gram. Water was added to one-half the saturation capacity of the soil. If this quantity was found to be too great, it was afterwards reduced, but this was the case in only a few instances. ‘The pots were weighed, placed 0n seales three times a week, and water added to restore the loss in weight. If the plants needed water between these weighings, such quantity was added as appeared necessary. The object of the weighing was t0 maintain as closely as possible a constant amount of water in the soil. A A few of these experiments were conducted in a greenhouse be- longing to the Horticultural Department, and a number were made on trucks covered with wire mosquito netting, The trucks were pulled into the house when a storm threatened. Later experiments were made in houses covered with canvas, These houses appear to be very‘ well suited to pot experiments under our climatic condi- tions. They are much better for this purpose than glass houses for the reason that the circulation of the air is considerably better and the house does not become so heated as a glass house would. Some of these experiments were carried on in houses with glass roof and canvas sides. This also appears to be a good form of house for our climatic conditions. A house with glass top and wire mosquito netting sides is also being used. In some respects this is better than the canvas house, but in other respects it is not. "The canvas houses are somewhat cooler. The open house is hotter, but the plants are of heavier growth than in the canvas house. REL-ATION OF DEFIOIENOIES OF CROPS TO ACTIVE PI-IOSPHORIC ACID. Results of the pot experiments so far as phosphoric acid is con- cerned are presented in Table The soils are divided into a numb-er of groups, according to the quantity of active phosphoric acid contained in them, The number of the group represents the maximum quantity of phosphoric acid in the soil in milligrams per 100 grams. That is to say, Group 1 comprises such soils as con- tain 10 or less than 10 parts per million oi” phosphoric acid, or 1 or less than 1 milligram phosphoric acid in 100 grains, In Group '2 are soils containing 10.1 to 20 parts per million. Group 3 contains 20.1 to 30 parts per million and so on. Some of the groups are not represented in our table and some are‘ combined, on account of the small number of soils contained in them. 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Mzm NZ Java 5m Em WM. $20 Sm éfiasw fink .>Q_§.Q , m w ii. 1| IQRoQ L50 019E AEQ m.“ wifim 23.. $23 1 m ._.:$Ew6mx@ “om o>So< .n Q5975 N‘ Afi I PS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .........AfluO0w vwfiuo>< m . €fii~mpwflg Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ind? ~m=w>dpw flOamDOm A? . , . . . . , . . . . - - . . . . - . . . . . . . . . . . . . . . . . . ¢ . . - - < < . . . . . . - . . . . . . . - . . . . . . . . . . i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155A: >€idw Qi@ T I . . h . . m 1w la; .55 E 3 w i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Ad? MQBQ GOumSOm ®~I% ... ‘ . Q ‘ . . . . ‘ . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . Ed? kibam finm£3flu@ QT l T . . . . . p» . . . . . ‘ . , . . . . . . . . ‘ 4 . . . . . . . . Q . o7m 12L I....=H~MX wsw o2 my" . . . . , . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . ...E.~o_ @255 ma»; M. , . . . . .m . . . . . . . . 4 . . . . . . 4 . . Q % , . . . . ‘ . . . . . . . . , . . . . . . 4 ‘ . w , w 1w lwTm .. 5.60 >5 Qm 1E m; mm QQ ‘ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..:?§m ficfioz H; .2520 i820 ammo 50:18 W W. M75 Mz as". E 5 mw 822w dEo Em 62:5 66¢ $2.2» m m w. woiwm \l ||||| 55g -55 oionfl uwmfi Wm. “EMF; :2 -32 .1 m ifiiivamv pom $353» d. 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JEOD mfi mfiw nQm. mJlm m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . .. 8M2 moniker o Q Ewing @.N M-aw . . . . . . . . . . . . . . . . . . . . . . . . | | 1a .. .1650 we. m3 m. m ow mwm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MM. 1mm mfiwwwnwm w? .... . .. ..... .. m EZEETMMQ w é J1. .... ..www N“? 3. ........ a .... 1 i.» . . .. m ................ .. ..a§ >20 82a aw I . Q2 ma 2w. 5v mm. 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H . . . . . . . . . . . . . . . . . . . . :8..6_ 2i .652 u? ad Wm. m Nd ad . . w o-ix @~§ Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - ee-i é-@ Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 .1 ¢-£% X¢X Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q3 ma . . . . . . Q Q3 Q3 am 8 Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . am .w 8.2; aofisow momQ 9w Wm. . . . . . . . Q wdw QM: Wm Www Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..w .w 15$ 2E éotoz $2 MUM“ 3.x Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - . . . - . .-E@o< . . . . . . . . . . .. . . . Q ma. aa . . . . . E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3m 2E .8 uaam £8.62 bngogm 3m Nwlwllwlh blaiioaaoomlm a-mw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655C dEaqU 58o .5228 NW. Mzm MZ $50 3Q 8m n u. i888...“ $30 Sm .385 .23 $25.3 m m “a 31am .l||l|||l| .533 E3 012E oflwQ m. m. 3G5 s2 ii . m Javflvzax» 3Q @383 _ d Ufld a maflobG _5()__ wflLfilwTofi . tukaumafi QQ Now . . . . . . . . . . . . . . . . . . . . . . . . w muolnhmnm .....@3._U: w. . . . . . . . . . . . . . . . . . . . . . . .. Q . &~ . ¢u@ @-¢ . . . . . . . . . . . . . . . . - - . w Q |© . . . . . .EO@ ©A® mZN Q . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -%N_O OONN> 5H a=o~U|< Spam. . . . . . 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QQ . . . . . .EO@ .@»% @.@ Gé Z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - JAQE QOuamdi 7 a 95ml 02$ mEAEU aéwkw is“. nozmfi T 5E MZ dam» am 3m Wm. 4399a $0.6 Sm .382” .33 $2.2» m m we vain.» 58cm L50 ozama |floQ Wm wEnE E04 18.3 1 .._ énwfiiwnnv “om v3.34 A .3 Ufld .3 an.» 3 was a 35.20 wTQINNé ...Esm=2 3. m2 I34. 13.500 3m m film; .._Esm=z i“ wTfllmflz .4582: E mi lo? ;....=so w: fiéifié ...€sm=s N»: m2 I24 ......E8 w: . . . . . . . . . . . . ouiwmsohwflckouvmuw$>< . . . >20 coawsom momfi . . . . $2» c$w=< £2 ESQ: aofiifi Efi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ‘ . . . . ...................i.................aw_uawmnw>, S: 152w wfivwfilwmAz .:u.§.._w=E w.» a. 3m www mam“. Q . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .....mom 3m 5w 22.514 mink mw.@N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .N$ Ofl QQZOMU Uwdh0>< wTfilwTfi . . éigmsi n6 ma . . . . . . . . . . . . . . . . . . . . . . . . Q m. 1w IHTm . . . . IP80 flow “.3 . . . . . . . . . . . . . . . . . . . . . . .. m w um. lw In ...€9§> ca ad . . . . . . . . . . . . . . . . . . . . . . .. QQ . . . . . .Q.~C@ ®.® M.N M.@N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .BdO_ ~nwv§dm Q5 muwluTn ......n._oo~..~.v Q3 . . . . . . . . . . . . . . .. w N~l~m|h IQ . . . . . JCOO NJ NJ ‘NM. ma: w . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..qudo_ hfifldm Qouandm Nam . “av .395 nlwlié Zitfiooqww Qww . . . . . . . . . . . . . . .. . . . . . .. m wlmlwum ....§@n>>@.~ E . . . . . . .. . . Q w In. . . . . . .EOU Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .530 hi? OUQHQQ .. 5m a=oeo|< vine. wTfilumuofl . wufimsfi m.» ad . . . . . . . . . . . m w nw lwwi .320 Wm fiw . . . . . . .. . . . . . . . . . . . . .. Q 3% |w u“. . . . . . .980 Q5 ma. Q5. mam mam QQ . . . . . , . . . . . . . , . . , , . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . ...E.8_ 2s cwfifi Rm “am a=o~w|< Baum. QTa 121» . . nofiao i. ca Q3 Qww onm m . . . . . . . . . , . , , . , , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , _ . . . . . . . . . .953 unmzfiagnm v2 .35 m2 "mm @220 m L» lwmi imEw fin 1m . . . . . . . . . . . . . . . . . . .. Q Nwlwmllwmla . . . . . 450D 9m w. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .%_a_0 "mm as2w|< v3.9a $83G 5.30 .28» 605i. T 5E Mz is s» s» WW 52:». dfio 6m .385 .23 $26G m w we 3am |I.|i avkoq LS» 28% uuwfl w. m1 22m 2% éé. 1 m ._._58m.$aw@ 3m $2.034 .3 3 S mfi5ou¢ firm-r m. . A. 1 rnF.‘ BQ 3 m6 E a m 3 N E m 8 E P é Q Q B / \. MQBE \ 4 \7 \\ LmfiSm blsmblobG LQQ QmQQQ fir". w. .25 wfiwzo: o»~>oiawno._o WZNWQMWN m? Qfi Qdm “v.3 Qmfi v.3 m8 mi . . - . . . . . @.X ?-§ .?-§ %~§ Q-fi 1.x . - - . - . . . . 1 a - - sawmvk Qwfiw; 5P6 F60 8 m“ 2 $3 8 I 2 93m M323» 3.53 w. m. m _ .565 duqofifluoanfl aom 3 hawflflsmlwu .02 HHM¢H The average corn crop is eleaply related to the quantity of active phosphoric acid in the soil. Soils containing less than 3:0 parts per million of active phosphoric acid are highly deficient in this form of plant food for corn. Soils containing up t0 190 parts pep million are deficient, PLATE I.—-Four soils of Group 1. Note the effect of phosphoric acid. If the soils contain less than 3O parts per million, about 9O per cent of the crops are deficient; if between 30 and 80, from '70 to 83 per cent are deficient. Over 80 pairts per million, the probabil- ity of a deficient crop decreases from 65 t0 44, but the number of soils studied containing this quantity is too small to draw decisive conclusions, M" \ ' i‘? utufl.’ w __57__ DEFICIENGIES FOR SOILS. The conclusions "in the preceding sections were drawn from a consideration of all the crops grown in the experiments, without regard to the number grown upon the same soil, the size of the crop, or other conditions which should be considered. In this part of the Bulletin, we will form our judgment as to the needs of the soil, SdflOlf) JO SIIOS JTIO&——'II ELLVTd? from these experiment-s which are, in our opinion, entitled to the most weight. In some cases, the crops are so small as to be of doubtful value, while in others conditions were unfavorable to par- ticular crops. We place the most emphasis upon the results with the corn crop, -_—5 8— because this crop was, on the whole, the most satisfactory, and more crops of this kind were grown than of any other. Hence, when the results of the tests on the same soil are inconsistent, we attach more weight to the corn experiment than t0 the others. Some of the r grass and wheat experiments are of little value. Seasonal condi- tions were, as a whole, not very favorable to goo-d results while these crops were being grown. One series of corn crops was grown in the fall. The cool weather caused the corn to grow much more poorly than it does in the spring or fall. The corn crop appears to be, on the whole, more sensitive to phosphoric acid than other crops. Where corn is very deficient, mustard is only deficient, A sufiicient- number of comparisons has not been made to warrant definite statements regarding the ability of various plants to assimilate phosphates, but this phase of the matter is being studied. After due consideration, we have decided that the deficiencies of the soils are as shown in the following table, This table contains all the soils of Table 23, excepting one or two eleminated for the reasons given above, (See Table 25.) TABLE N0. 25~Deflc1enc1es o! Soils. DD _ S Very deficient. Deficient Not deficient Group 1.. 306, 310, 316,324, 336,344, 819,820,821, 173, 342 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 822, 85 1138. Group 2. . 97, 131, 314, 334, 340, 816, 817, 834, 843, 141, 180, 332 . . . . . . . . . . . . . . . . . . . . . . . . . 1589 859, 1120, 1126, 1136, 1140, 1587, 1590, , 1130, 913, 1124. Group 3.. 108, 832, 860, 941, 1592, 1119, 1247.. . . . 76,1551, 137, 174, 178,82 9,893,911, 1123, 1578 Group 4 328, 330, 1577, 1582 . . . . . . . . . . . . . . . . .. 910 Group 5 127,128 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Group 6.. 134,851 . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 940, 935 Group 7.. 211, 818, 1134, 1205, 1597, 1598 . . . . . . . . . . . . . . . . . . .. Group 8. . 932, 939, 982, 1581, 1593, 1596, 1599.. . . . . . . . . . . . . .. Group 9. . 933, , 1580 . . . . . . . . . . . . . . . . . . . . . . . 1600 Group 10.. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1133 Group 11. . 1203 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Group l3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 845, 1206 Group 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Group 16.. 1131, 1595 . . . . . . . . . . . . . . . . . . . . . . . . . . . 1204 Group 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Group 32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934 Group 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Group 39. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Group 40.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831 Group 42. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 912 Group 60.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H"; .. 1976 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ' The results of this table are combined in Table 26, in which the number of soils decided to be very deficient, deficient, and not deficient, are given. Also the percentages are given of the total number in the group. Of the 38 soils containing less than 2O parts per million of active phosphoric acid, we find 32 highly deficient, 5 deficient, and 1 sufli- 59 cient. The sufficient soil (No. 1589) had only one pot experiment made on it, and the results might very possibly have been different had more tests been made. We have already seen that the corn crop produced on soils of these groups with no phospho-ric acid are only from 19 to 26 per cent, respectively, of the crop with phosphoric acid. Soils containing 20 parts per million, or less, 0f active phosphoric acid are highly deficient in phosphoric acid. Considering the table further, we find that the percentage of very deficient soils decreases rapidly from 8'7’ per cent in the first group to 14 per cent in the fourth, after which it decreases slowly to the 11-17 group, after which there is a sudden increase. One soil, how- ever, makes a“ great difference in the percentage in these groups. TABLE N0. 26—Number and Percentage o1 Deficient Soils Grouped Ac- cording to Content of Actlve Phosphoric Acid. Number of soils Percentage of soils Group DD D S DD D S] No. l . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . 13 2 0 87 13 0 N0. 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3 1 83 12 4 N0. 3 . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . 7 10 1 39 55 6 No. 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , , . . . . . . 1 5 1 14 71 l5 No. 5 and 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 4 2 14 57 28 No. 7 and 8 . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . 2 13 O 13 87 0 No. 9 and 10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 5 2 l3 63 24 N0. 11-19 . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . , . . . . 1 5 5 9 45 46 No. 32-42 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 O 4 33 0 66 Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 47 16 The percentage of non-deficient soils increases with fair regu- larity throughout the table, though there are some breaks, notably in Group 7-8, all soils in which are deficient. In Groups 3 to 10 are 55 soils, 12 of which a.re very deficient, 3'7 are deficient, and 6 appear to yield suificient phosphoric acid. That is to say, about 11 per cent are not deficient. The average corn crop without phosphoric acid is from 34 to '71 per cent of that with phosphoric acid, We feel justified in drawing the following conclusion: Soils containing from 3O to 100 parts per million of phosphoric acid soluble in N/5 nitric a.cid, are, as a rule, deficient in phos- phoric acid, and the extent of their deficiency is related to the quantity of active phosphoric acid, Group 11-19 contains only 11 soils. Nearly 5O per cent are not deficient. We draw the following conclusion, subject to modifica- tion when a largerinumber of soils are studied: a Soils containing from 100 to 200 parts per million of active phosphoric acid are possibly deficient in phosphoric acid, the chances being even that they are or are not deficient. That is, of 10 soils in these groups, 5 will probably respond to phosphatic fertilizers. Groups 32 to 42 contain only 6 soils. Such soils are likely not to be deficient in phosphoric acid, but the conclusion is likewise sub- ject to modification from further study. RELATION OF ACID OONSUMED AND FIXATION FOR PHOSPI-IORIC ACID. The preceding discussion was based upon the phosphoric acid taken from the soil without regard to the fixing power or acid consumed. These values are given in Table 24, and their effect upon the results of the work will be discussed in this section. A summary of the results is presented in Table 27. ‘There is no general relation between the acid consumed, and the fixing power of the soil in the different groups, beyond the fact that average “acid consumed” in the first two groups is considerably lower than in all the others, That is to say, the soils of this group are, as a rule, non-calcareous, although calcareous soils are found within the group. The soils of the other groups, on an average, neutralize 25 per cent of the acid, and contain the equivalent of 2.5 per cent carbonate of lime. We consider such soils as calcareous. Non- calcareous soils are, however, found in all the groups. Table 27 also shows percentage of acid consumed by the soils which do not conform to the general behavior of the soil as regards deficiency. For Group 1 and 2, the soils behave as highly deficient; so soils which are deficient, or not deficient, are considered as ex- ceptional soils for these groups. In Groups 3-10 the soils are pre- vailingly deficient; so soils which are very deficient, or not deficient, are considered as exceptional. Soils very deficient are considered as exceptional in Groups 11-19 and 32-42. I We find in the table two exceptional soils in Group 1, having acid consumed of 0 and 2, respectively. In Group 2 there are 4 excep- tional soils, with acid consumed of 0, 100, 5, and unknown. The greater the acid consumed, the more soil material is brought into solution by the solvent, and the greater the probability that the dissolved material has exposed some of the protected soil phos- phates. A high or very high acid consumed should, therefore, indi- cate the possibility that the soil may belong to a lower group than that in which it‘ is placed. I In Groups 1-2, we find 3 of the exceptional soils with low acid consumed, and 1 with high, "The former might be expected, the latter is indeed exceptional. In Group 3-10, we find all the very deficient soils to be all soils of low acid consuming power, much lower than the average. Two of the not-deficient soils have an acid consuming power higher _.51_ than the average for the group, and 4 are lower. No general con- clusions can be drawn from this data. . The results for fixing power are tabulated in Table 28. N0 re- lation can be seen between the group to which the soil belongs, and its fixing power. _ The fixing power of a soil tends to place it in a higher group than the one in which it is found. The higher the fixing power, the greater the correction. p No relation can be traced between the percentages fixed by the exceptional soil, and relation of the exceptional soil to the others. If we attempt to correct for the fixing power of the soil, we find, in some cases, no great change, only from one group to the next one. There are, however, soils on which a considerable change will be found, but on some of these the calcareous matter dissolved in- dicates that they really belong in a lower group. As we have al- ready stated, we are unable to correct for acid consumed. In Group 1, soils 336 and 11.38 would probably be changed to Group 4 by correction for fixation, though reduced by acid con- sumed. Both these soils are very deficient, and evidently belong to Group 1, Since the phosphates dissolved in Group 1 do not prob- ably come from calcium phosphates, we believe no correction should be made in this group. In Group 2, soils 141, 332, 1583, 1587', 1590 would be perhaps raised to Groups 4-8 by correction for fixation. Three of these soils are deficient, and two are very deficient. Since a large part of the phosphates dissolved comes from phosphates of iron and aluminium, we are doubtful about making a correction. In Group 3, soils 829, 832, 941, 1207 would be raised to Groups 4-10 by correction for fixation. Three of these soils are very de- ficient, and 1 is deficient. It would appear that the correction should not be made. _ In Group 4-8, 1 soil, 982, would be raised considerably in rank by correction for fixation. It- would appear from the above, that correction for fixation should not be made in applying the analyses of the soil to the results of pot experiments. We believe, however, that the fixation and acid consumed should be taken into consid- eration. The matter is worthy of further study. -_5g__. ad ca. oA o a Qm o ad o o . . . . . . . . . . . . 2a m... 2: 2: c3 2: o2 2: 2: . . . . . . . . . . . . o o o ~ o o ~ fi o . . . . . . . . . . . . w w w m m v w N fi . . . . . . . . . . . . fi ~ o o m w w m ~ . . . . . . . . . . . . o fi o N m o w. m H . . . . . . . . . . . . fi w q m ~ m w 5 NH . . . . . . . . . . . . ml» 3|: 2|» ma» i w w N fi ..|||.|l||||.|ll- .2520 ||||||||||||||||||||l|.|||||||| "lug-lull, 'lll.l|l|ln|llll-llll|lill|.|la|.|llll|ll| ||||l I . . . . . . . . . . . . . . . . . . . . . . . . . . . . ZQQ “wvflsmcoo wwwfiafivm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Iflmgmwaoz fixbm “Pélfimn ES’ . §§él=wm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 . . . . . . . . . . ll >>@_QQI~>OQ 51.8 “c ~wnflszlueismnou E3» Qgzouwn :8 8 £38532. 03¢... S nassfimla dz mung. . . . . . . . . wwwmmwfim 3n v-IOQCNOOO flfg o‘ . >3 Qlwvtfiwv-qo ofi 2s vHNWJOQC § QDNKOCQv-n-u OOQI-iwlflv-IO v-q QHOCVJv-n-IO . . . . . . . ............._........................................................0@E@U@aOz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - .aflv@o@wfi. %u0> "amen wmcowuawoxm an v88 uwnunookwm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . dww$>< ..IZMM_JNMMWUMMZNMW_ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...:E=SMa§ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ¢ . . . . . . . . . . . . . . . . . . .....8=Sn82 ‘ . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . "v86 Qmfléssm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....2§Efi.z Hmom wO uQQESZ Q73 21¢ m1» i .2530 sunosuon E5 8 nseflfl u. naflpsvmlwu dz mafia... COR/V POSS/B/L/TY //v% Bus/was m K Q Y o0 00/ Q Q Q Q __55__ PHOSPHORIC ACID REMOVED BY CROPS. In a number of the pot experiments shown in Table 23 we deter- mined the phosphoric acid in the crop, and calculated "from this the amount of phosphoric acid withdrawn from the soil which received no phosphoric acid. Assuming that =10 bushels of corn requires 25 pounds of phos- phoric acid, and a weight of 2,000,000 pounds of soil to the acre, we have calculated the number of bushels of corn which would be produced by the phosphoric acid withdrawn from the soil, One bushel of corn we estimate to require 0.00156 grams phosphoric acid per pot ot 5000 grams of soil. The results of these calculations a.re presented in Table 29, and a summary of results inyTable 30. We find that the average pos- sible corn crop increases regularly with each group, the only excep- tion being Groups 9 and 10, containing 3 soils and 3 crops. -Right here we must again call attention to the fact that these crops were - grown under’ diverse conditions, and the climatic conditions were sometimes not favorable to the crop. But we feel that the relation between the average corn possibility and the quantity of, active phos- phoric acid in the soil is very significant. ' The first two groups of soils, which are highly deficient in pho-s- phoric acid, have an average possibility of 4.5 and 12.5 bushels of ‘corn, respectively. Groups 3 to 10, the soils of which are prevail- ingly deficient in phosphoric acid, as we have pointed out, have an average corn possibility of 19.7 to 26.5 bushels of corn per acre—the variation is not large. Group 11-19 and 32-é2 have an average corn possibility of 50-60 bushels per acre. W e have already pointed out that a soil may be highly produc- tive, and yet zippear deficient in a po-t experiment. 1f we consider the IILCLILTTYITIU/HZ corn possibility within the groups, we find that, like the average corn‘ possibility, it increases with the quantity of pl10Spl10TlC acid extracted from the soil by N/5 nitric acid, with the exceptions of Groups 9-10 and 11-19. We find a maximum possibility of 31 bushels in Group 2, from 37 to 59 in Groups 3-10, a.nd from 94 to 104 in Groups 11-12. It appears that soils may provide sufficient phosphoric acid for large crops, and yet respond to applications of pho-sphatic fertil- izers. The response may, however, vary with climatic conditions. We have already pointed out that the application of pot experi- ments to field conditions is a matter which we shall study. Q 11b ll-M IQ . . . . . .fluO@ wfi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . Uflfiw Ofl@ Muflflwifldnc dmlmw . . . . . JZQU O6 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.50 Muflfivwflduo 31w 115$ . . . . 1580 >3 mm om owns. Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .582 ceamnom H 82.6 mm 1w 11om1+ . . . . . .580 81S fi m mwoo. QQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . zu .m 438w 26 aims“? wwm m§ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . duflw>< x Q - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 u w no m Uudaafls Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1w .w hd? hZw>w~uA~QawflOm m lzlmfllm 1.: 3:2. woLwm mm : v50. Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.2: hwcsm 355A T‘. Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 w 1» 1lw 1m . . . . . .580 812 3 NH $3. 0Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..E5m 2E £882 i 1w . . . - a . - . , . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . - . . . . . . JuuOmw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85ml kfifldw QG@ wuflfiwwfldus w 1» 11w 1v . F80 81A oi. 3 mama. QQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..E~o_ >388 2G 58:20 31w 11o 1v . . 11:80 51A G w $8. OD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....?8w 26 238a t Iw u @ . . . ¢ . . . . . . . . . . . . . . . . . . . - . . . . . . . . - . . . . - . . - . . . . . . . . . . . . . . . . . . . . . . . . a 31a 1131» IP80 we 1M osw 5 3g. QQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .582 8838i w 1o 1|m~1¢ 11.580 810 n8 w wmoo. QQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8m 2E £8082 “N Q9050 31a 112$ . . . . 2:80 $01M we 3 owns. QQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1:82 =8£5i w $ . . - ' - % . . . . . . - . . . . . . . . . . . - . . . . . . . . . . - . . . . < . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - . 5% fi-Q . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . flvws0>< a 1w 11H 1m. . =80 8.2 .1: m cmoo. DD . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .582 .882 aananvnvmsw 31w I24 . . . . 2:80 81A mm a $5. QQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Zwsam 2G £8582 m 1w |§1m . . . . 1:80 $13 8 m $2.. QQ £ l|§ 11|£ $ . . . . 1 x . . ~ . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - . - . . . . - . 4 I fi IX . . . . . § . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . 1 31¢ 131» . . . . . .580 31M Qmw v amoo. DQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82: .885 2E ancanwsvmzw $1» 121m . . . . 1:80 @013 3 a $3. QQ . , w 1w lwTe . . . . . .500 RI. 9mm w , wmoo. QQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .882 .853 2E whsawwnwhc w .l.© . . . . . écOmw m. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Eda: hflflflm ®fl@ dflflfifiwflwmfl@ J .5820 .33 .98 E étizw . . 8m. 53 5m c6.» $288 .8 wotum .550 .w28m 5E5.» .53 258 18D 1:83.. 8 “=2 182E -2225 38a 43m 03a 8 23» uflonnmonmiam .02 HANQH. an 3m m“ aw 8m 2m ueqmnN u Moquequq __57__ mué IL. |n . . .. Eco wok: w B ammo. Q. . . . . ‘ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . zm .m n52 noewaom mowfi r |\ . Sm: w; w . . mvwhfiaw ...”... in“ at: 2 m m. .................................................................... . . . . . . . . . .w .w E0 =25". as ' \ ~32... aim w . . mm.w_\wfi_ Ab. dsw 3: 2 m “Mm”. m ...................................................................... . . . a w gm E aesz a: . . . . . .fl.~®@ Q . . . . . . . . . . . . . . . ‘ . ‘ . . . . . . ‘ . . . . . . . . . . . . . . ‘ . . . . . . . . V . . . . . . . . . . . . . . _ . . . . . . . . lads ~mfifldw 05% O©whdg . . . . IQuOU Q . . . . . . . Zéqwshfifldmmflflkflmdfidawmw w l© . . . . . JCOQ Si». Rim h Q . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . wvflflm Ofl@ k0 Uqmmn%=wnvv&~ud©& \ . . . . . .E.~O ©.® . . . . . . . ‘ . . . . _ , . . . . . ‘ . . . . . . . . . . ‘ . . . . . ‘ . . . . . . . . . . . . . . . . ‘ . . . ‘ . . . . . . . . . . . . . . . . .E.NO_ ~nN_O Ofiu8fl< fld@ w Ly E Q E mm é... .... a ................................................................................. .. OM54 I »\ . . . Nam? llllll - . . . . . . . . . . . . . . . 4 . . . . . . . . . 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ¢ Bin; flnvmi; m%|w_\m£_ .. .9 Sow 2T2 3N mm mwww. w . . . , , . , . , . , . . . . , . , . . , . . , . . , , . . . . . A . A . . . . . . . . . . . . A . . . . . . . A . 4 . 4 . . A . . . . . . . . . . . . . ..a8_ 2% =ow=B 5w @ IR . . . . . .G.~O@ @ . . . . . . . . . . . . . 4 . . 4 . . . . . . . . . . . . . . . . . . . . . . 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E.NO_ ~hifi>fihw Owwwkflg 2&3 .... 3A. E ma $2. Q ......,.._,...,.,.,>.51:;xxRNAUHHNIHHMHN“anH< I \ . D M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ‘ . . . . . . . . . . . . . . . . ‘ . . . . . . . . . . . . . . . . . . . . . . . . . . . QAN? ¥Q2Q flsmflnvm WQTME7 wfiww mfiw a wm mwwm. m .:.;...;.....;;..:;.;.:1;‘v.z...4.,;....:.....1........A2» QnWAEMw ncpgom “m2 oT¢\2|~. . . . . 1:80 97M owm vw mwmc. QQ ...... ..E@o_8aa_mmmm . . . . . JCOQ Q . 4 . . . . . . . 4 . . 4 . 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $20 hflOum muuOwkrfiunw ml Li. .. . H H E8 2T: 8W a a5 an .......................................... . ................................... N 4w L1 ... 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Ea 5m End =8a2u m m. “o woivm .030 aviwm éfimna .53 012E AED m. n én>< 8 “=2 48am u w, kisvm .3295 K dvsaflnaolzam 3s 3 63¢ aianananmla» .62 NHN< . imzdamfls QM fl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .520 flmdfld; N |@ ‘N |@ . . . . . .EO@ ew-N m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..a.NO_ %wv.idm QOhamfi@ mm n 1w 113$ . . . . IIEOO woéQ in m» 5Q. w . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . ...S.~2 >EEQ 26 .522. m3 n nw |I|m 1.1.500 81: w S. owwo. m w n» léTw . . . . 1.5.5 8:2 h Na $3. Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $2» >21. owfiwq s» amlw Iw [v . . . . . EGO w G Nwao. QQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . éfiag 2i ovfiau hNw “Q o» mm mnsouw méfi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jwwduw>< M . . .U.~dum52 N wm Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .%.§O Eam5< . . . . .EO@ ® Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . u o -%.EU QOawDOm Zuw IQ an .Eoo 2T2 mm SQ owfi. m . . . . . . . . . . . . . . . . . . . . . . . , . . 1. . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..E§Zmm nflvbw? 3w wT~Q|@To_ . .9332 £15 3 g 83. w w l© . . . . . .EO@ © £8. Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . o 0 Jmflz OONd> 5Q 8 Q wnsoeo wTw |~m|¢ . 12.500 new... mQ am wowo. m . , . . . . . . . . . . . . , , . . . . . . , . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65$ q . o; 1a-... ...........Q s-.. 3 a a”... Q ................................................................................. .. Qmmawmmw “MM. mwé i» in. . . . . . Azoo 3A. Qm h 5S. Q . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65$ 2E aaasQ wQm 5Q E2 a mqsfiw m LQImTm 1d 582%., aim 3 3 mono. Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . .E..8_ >w§m 03.6w 3.3 M . . .@~fiwmiz rfi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Z %.N_O MQEQ iOwwnwOm m |S|3$ .:w:$w=S 81mm w 3 Ewe. Q . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . 4w .m =52 zwawm 83% mama M Q . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jaw? QOQmSOm M @.,~.wam5§ m. Q . . . . . . . . . . . . . . . , . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .@ Eda; 5G7.» £0.20» QCQmQOm 6.6a doh. E W. dfiifiw NR. Ea 5Q E3 Quafiu WW. we wniwm .920 dwmgvm 5E5.» .500 @193 éuQ m m -33.. s E2 -22“ NW -565 “mama? .1 M dvsasnaulzam 23 3 .034 aionnwcnmlwfl .62 HHQQH. 1 u: lw$nwfivit§ iuls. .0..|.....r.1.|:..4. Hhwuwi TABLE N0. 30—~Average Corn Possibility and Availability o1 Phosphoric Acid Corn equivalent Availability (bu. per acre) percentage Average. Maxima. Average. Maxims- Group 1—9 soils, 11 crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 9 27.0 Q Group 2~l3 soils, 13 crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.5 31 28.8 81 Group 3—6 soils, 6 crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.8 36 31.2 52 Group k6 soils, 7 crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.7 37 18.4 a Groups 5 and 6-6 soils, 6 crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.4 42 14.4. 25 Groups 7 and 8—13 soils, 13 crops . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . 26.5 59 11.7‘ 2i Groups 9 and 10-3 soils, 3 crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.0 39 7.9.‘ l3 Groups 11—19—-4 soils, 5 crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.5 101 11.1 5 Groups 32-42-5 soils, 6 crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60.7 91 4.7 7 AVAILABILITY OF ACTIVE PHOSPHORIC ACID. Assuming that the phosphoric acid removed by the crop comes from the phosphoric acid extracted by N/5 nitric acid, we can calculate the percentage of phosphoric acid taken up by the crops from the data given in Table 23. These calculations have been made, and the res-ults are presented in Table 29, a summary be- ing given in Table 30. We term the percentage of the active ‘ phosphoric acid taken up by the crop, its availability. We do not xvish to say, however, that the phosphoric acid taken up does not come from sources other than that soluble in N/5 nitric acid. Considering first the average availability, we find it rises from 27’ to 31.2 i.n the first three groups. This rise, however, is of little significance-we can almost say that the average availability is the same for the three groups. If the phosphoric acid dissolved by N/5 nitric acid comes from the natural phosphates 0t lime, we can not expect them to have a high availability. An average availability of 27-31 per cent for the phosphoric ,acid of the first three groups must lead to the conclusion that some of the phosphoric acid taken from the soil comes from other sources than that soluble in N/5 nitric acid. In other words, the assumption we started with is not justified, at least in these three groups of soils. The first group of so-ils, those containing less than ten parts per million of active phosphoric acid, probably does not contain any phosphate of lime at all. The 7-10 parts per million of phos- phoric acid dissolved represents the solution of a portion of some highly insoluble phosphate. The availability of the phosphates based upon the portion dissolved, is thus increased. The availa- bility should be based upon the total quantity of the insoluble phosphate, which is not known. __7()_ The considerations which apply to Group 1 also apply to the other groups, their importance decreasing with the grade of the group. In other words, some of the phosphoric acid withdrawn by crops comes from the less soluble phosphates. It is, of course, possible that other phosphates of importance may be present in the soil. This is apparent when we consider the high maximum availability of the active phosphoric acid in the diiterent groups. While not decreasing regularly, the percentage availability de- creases with the grade of the group. This decrease may be be- cause the assumption is incorrect, that the phosphoric acid with- drawn comes entirely from the N/5 nitric acid extract. It is possible that the availability in the higher groups represents more nearly the availability of the active phosphoric acid, than that in the lower groups. The matter of the availability of the phosphoric acid of the soil is being subjected to further study_ SUMMARY AND CONCLUSIONS. 1. The plant food withdrawn from the soil by the plant de- pends upon the form of combination of the plant food, its protec- tion or non-protection by encrusting particles, the action of weath- ering agencies upon it, and the nature of the plant. 2. The composition of the soil extract, by any solvent, depends’ upon the quantity of the phosphate exposed to the solvent, and its solubility under the conditions of the extraction, the solubility of the material which protects phosphates, and the fixing ability of the soil for phosphoric acid from the solvent in question. 3. Fifth-normal nitric acid dissolves phosphates of lime com- pletely, but dissolves such iron and aluminium phosphates as usually occur in the soil only to a slight extent, It thus distinguishes be- tween these two classes of compounds in the soil. 4. Fifth-normal nitric acid may not distinguish between phos- phates which have unequal values to plants. Soils should be com- pared which probably contain the same kinds of phosphates. 5. One per cent citric acid has a lower solvent power for min- eral phosphates than fifth-normal nitric acid. The solvent powers of other solvents is‘ discussed. Fifth-normal nitric acid is pre- ferred. 6. Soils absorb phosphoric acid in solution in fifth-normal nitric acid, and other solvents. '7. The percentage of the added phosphoric acid absorbed by the soil increases as its content of oxides of iron and aluminium increases. 8. Residues from the extraction of the soil with fifth-normal nitric acid and with stronger acids, may have nearly as great ab- sorbing power as the original soil. 9. The phosphoric acid absorbed by soils is no-t extracted by the first extraction with fifth-normal nitric acid, but its effect is evident in the fourth, and-sometimes in the sixth, extraction. 10. Natural soils resemble soils which have received potassium phosphate in their behavior to fifth-normal nitric acid in succes- sive extractions. ].1. Soils containing little or no phosphates of high solubility give practically the same amounts of phosphoric acid to successive extractions. 12. Soils which have a fixing power of 80 per cent or less, have a fixing power of about half as much from N/5 nitric acid solu- tion. Soils which have a fixing po-wer over 80, may fix equally as high a percentage from fifth-normal nitric acid. 13. When the significance of the phosphoric acid extracted from a soil by fifth-normal nitric acid is to be decided, the fixing power of the soil for phosphoric acid, and the acid consumed, should also be known. 14. Sulphate of lime increases the amount of phosphoric acid extracted fr-om soils high in iron. 15. Calcareous soils contain phosphates which are protected by the carbonate of lime from the roots of plants, but which are exposed by solution of the carbonate of lime in acid solvents. 16. The amount of lime and magnesia dissolved may be esti- mated from the quantity of acid consumed. 1'7. The quantity of material dissolved in second or succeeding extractions with acid is sometimes large. 18. It would appear that the lime and magnesia are present in highly soluble forms (carbonates and silicates), moderately soluble silicates and silicates of low solubility. _ 19. Citric acid dissolves less iron, lime and magnesia, than fifth-normal nitric acid. 20. It would appear that the phosphoric acid dissolved by fifth-normal nitric acid in excess of about ten parts per million comes from phosphate of lime. 21. Judging the amounts of phosphates of lime presented to the roots of plants in a given soil, one must allow for the de- crease due to absorption, and the increase due to solution of in- crusting material, so far as possible. 22. The author extracts the soil with fifth-normal nitric acid without correcting for neutralization. 23. It is impossible to maintain only one variable in pot ex- periments, though one may predominate. Soils may appear de- fieient for phosphoric acid and yet be highly productive without phosphatic fertilizing. . . 24. Soils containing less than 2O parts per million of phos- phoric acid extracted by fifth-normal nitric acid are highly de- a ficient in phosphoric acid in pot experiments. 25. Soils from which 20 to 100 parts per million of phosphoric acid are extracted by fifth-normal nitric acid are usually deficient ior phosphoric acid in pot experiments, and the extent of their deficiency is related to the quantity of phosphoric acid present. 26. Although the pot experiments were carried out under diverse conditions, the average corn crop is closely related to the quantity of active phosphoric acid in the soil. 2-7. Soils containing from 100 to 200 parts per million of active phosphoric acid are possibly deficient in phosphoric acid in pot experiments, the chances being even that they are or are not de- fieient. 28. The average possible corn crop, based upon the quantity of phosphoric acid extracted from the soil in pot experiment, in- creases regularly with the amount of active phosphoric acid ex- tracted by fifth-normal nitric acid. 29“. Soils containing less than 10 parts per million of phos- phoric acid had an average possibility of 4.5 bushels corn per acre. If they contained 10 to 20 parts, the possibility is 12.3 bushels. If they contained 30 to 100 parts, the average possibility is 19.’? to 26.3 bushels corn per’ acre. If they contained 110-420 parts per million, the average possibility was 50-60 bushels co-rn per acre. 30. The maximum possible corn crop also increases directly with the quantity of active phosphoric acid in the soil. 31. Soils may provide sufficient phosphoric acid for large crops, and yet respond to phosphoric fertilization in pot experiments. 32‘. Phosphoric acid is taken up by the crop which comes from other sources than the active phosphoric acid—-especially if the soil contain less than thirty parts per million of active phosphoric acid. i 33. The phosphoric acid removed by the crop in percentages of the active phosphoric acid, decreases with the quantity of active phosphoric acid in the soil. Special mention shouldbe made of the services of Mr. E. C. Carlyle in connection with the work here reported.