A l 78-123-4500-L TEXAS AGRICULTURAL EXPERIMENT STATION AGRICULTURAL A/ND MECHANICAL COLLEGE OF TEXAS // w. B. BIZZELL, President BULLETIN NO. 304 DECEMBER, 1922 DIVISION OF CHEMISTRY THE FIXATION OF PHOSPHORIC ACID BY THE SQIL B. YOUNGBLOOD, DIRECTOR, COLLEGE STATION, BRAZOS COUNTY, TEXAS STATION STAFFt ADMINISTRATION B. YOUNGBLOOD, M. S., Ph. D., Director CHARLES A. FELKER, Chief Clerk A. S. WARE. Secretary A. D. JACKSON, Executive Assistant CHARLES GORZYCKI. Technical Assistant M. P. HoLLEuAN. Jn., Assistant Chief Clerk R. N. Bunnows, M. A., Research Librarian; VETERINARY SCIENCE *M. FRANCIS, D. V. M., Chief H. Scnmn-r, D. V. S., Veterinarian V. J. BRAUNEB, D. V. M., Veterinarian CHEMISTRY G. S. FnAPs, Ph. D., Chief; State Chemist S. E. Assuav, M. S., Assistant Chemist IS. LOMANITZ, B. S., Assistant Chemist J. E. SEABRIGHT, B. A., Assistant Chemist WALDO WALKER, Assistant Chemist HORTICULTURE H. NESS, M. S.. Chief W. S. Ho-rcuxxss, Horticulturist ANIMAL INDUSTRY J. M. JONES, A. M., Chief R. M. Sherwood, B. S., Poultry Husbandman R. WARREN, B. S., Swine Husbandman L. LUsn, Ph. D., Animal Husbandman (genetics) _ _ _ l. MURPHY, Wool and Mohair Specialist G. J. L. N J. D. SUNKEL, Dairyman ENTOMOLOGY M. C. TANQuAnY, Ph. D., Chief; State Entomologist H. J. REINHARD, B. S., Entomologist . B. PARKS, B. S., Apiculturist . S. RUDE, B. S., Entomologist . H. Auzx, B. S., Queen Breeder ONOMY . B. CONNER, B. S., Chief . H. Lennon, B. S., Agronomist . B. REYNOLDS, M. S., Ayronomist . N. STROMAN, M. S., Agronomist; Farm Superintendent PEARL Dnummonn, Seed Analyst PLANT PATHOLOGY AND PHYSIOLOGY J. J. TAUBENHAUS, Ph. D., Chief COTTON BREEDING G. F. FREEMAN, D. Sc., Chief FARM AND RANCH ECONOMICS L. P. GABBARD, M. S., Farm and Ranch Economist SOIL SURVEY **W. T. CARTER. Jn, B. S., Chief H. W. HAwKEn, Soil Surveyor H. V. GEIB, B. S., Soil Surveyor FEED CONTROL SERVICE B. YOUNGBLOOD, M. S , Ph. D., Director D. FULLER, M. S., Chief Inspector D. PEARCE, Inspector H. Romans, Inspector . H. W001), Inspector J. KELLY, Inspector ‘J2 > mm>>§ >0 *- *- F. S. J. W J. SUBSTATIONS No. l. Beeville. Bee County I. E. COWART, M. S., Superintendent No. 2. Troup, Smith County W. S. HOTCHKISS, Superintendent No. 3. Angleton, Brazoria County V. E. HAFNER, B. S., Superintendent No. 4. Beaumont, Jeflerson County A. H. PRINCE, B. S., Superintendent No. 5. Temple, Bell County D. T. KILLOUGH, B. S., Superintendent No. 6. Denton, Denton County P. B. DUNKLE, B. S., Superintendent N0. 7. Spur, Dickens County R. E. D1cKsoN, B. S., Superintendent TA: of January 1, 1923. No. 8. Lubbock, Lubbock County R. E. KARPER, B. S., Superintendent No. 9. Balmorhea, Reeves County J. J. BAYLES, B. S., Superintendent No. l0. College Station, Brazos County (Feeding and Breeding Substation) L. J. McCALL, Superintendent No. 11. Nacogdoches, Nacogdoches County G. '_I‘. MCNESS, Superintendent **.No. 12. Chillicothe, Hardeman County A. B. CRON, B. S , Superintendent No. 14. Sonora. Sutton-Edwards Counties E. M. PETERS, B. S., Su erintendent D. H. BENNETT, V. M. ., Veterinarian *In cooperation with School of Veterinary Medicine, A. and M. College of Texas. "In cooperation with United StatesyDepai-tment of Agriculture. IOn leave. TABLE OF CONTENTS. PAGE Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5 Method of Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5 Effect of Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6 Effect of Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6 Effect of Salt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 7 Effect of Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 7 Effect of Ignition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8 Fixation by Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10 Fixation of Phosphoric Acid of Fertili-zers . . . . . x. . . . . . . . . . . . . . . . 11 Percolation and Fixation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Relation of Fixation to Composition . . . . . . . . . . . . . . . . . . . . . . . . . .. 17 Statistical Relations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18 Relative Fixation by Texas Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 21 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 21 BULLETIN No. 804 DECEMBER, 1922 THE FIXATION OF PHOSPHORIC ACID BY THE SOIL BY G. S. FRAPs It has been known for a long time that soils have the power of re- moving phosphoric acid, potash, and some other substances from solu- tion. This property, which is called fixation, was studied by soil chem- ists over fifty years ago, and is shown by the work of Way, Bret- chneider, Peters, and others from 1861 to 1865, and is discussed on page 235 of Fraps’ Principles of Agricultural Chemistry. Fixation tends to prevent the potash, phosphoric acid, and ammonia of the soil from being washed out, thereby helping the soil to retain these valuable forms of plant food. If fixation did not occur, in the course of geological ages soils would no doubt become highly im- poverished in plant food. Fixation hinders weathering agencies, in- cluding water, from removing plant food such as phosphoric acid 0r potash from the soil, but instead allows less important materials, such as soda and chlorine, to pass off into drainage water. This is an exceed- ingly interesting and wise provision of nature. ' Fixation also tends to prevent loss of potash and phosphoric acid added to the soil in the form of fertilizers, but on the other hand, it tends to make phosphoric acid of fertilizers less available for plants. Fixation also interferes with the chemical analysis of the soil, in that the soil holds back and absorbs part of the plant food which would otherwise go into solution in the acids used by chemists. This Bulletin is a study of the relation of fixation to properties of typical Texas soils, especially as related to the loss of phosphoric acid of fertilizers or to the estimation of active plant food in the soil. METHOD OF DETERMINATION As was shown by previous studies of other workers, the amount of fixation varies with time, temperature, concentration of solution, ratio of soil to solvent, and other factors. For the purpose of estimating the fixing power of Texas soils for phosphoric acid the following method was used: METHOD FOR ABSORPTION OF PHOSPHORIG ACID BY SOILS Strong Phosphate rS'olu-tion.—Make up a solution of dibasic potas- sium phosphate, and determine phosphoric acid (P205) in 10 c.c. Dilute so that 20 c.c.:.020O grams phosphoric acid. Weak Phosphate Solut-ion.—Place 200 c.c. of strong phosphate solu- tion in a 2-liter graduated flask and make up to volume. 6 TEXAS AGRICULTURAL EXPERIMENT STATION. DETERMINATION Bring 50 grams of the soil in contact with 200 0.0. Weak phosphate solution in a dry bottle, Well stoppered. Shake every half hour dur- ing the Working day, and filter at the end of 24 hours. Measure off 100 0.0., add 8 0.0. nitric acid, neutralize with ammonia, acidity with nitric acid, evaporate to about 75 0.0., filter and Wash if necessary, and determine phosphoric acid by the volumetric method. Run at least eleven soils and one blank on the solution at the same time. The blank should be run just as if it Were a soil. If the solution is made up so that 10 0.0.2210 mg, and if a is the number of milligrams phos- phoric acid found, then 10-a multiplied by 10 is the absorption in per cent. Otherwise it is necessary to divide by the quantity of phosphoric acid in the 10 0.0. of solution. Report results to nearest tenths p-er cent. EFFECT OF TEMPERATURE Effect of temperature on the absorption of phosphoric acid was studied by the method described above, the only variation being in the temperature. The solution in contact With the soil was kept five hours in ice Water, or five hours at room temperature, or five hours in a Water bath at 40 degrees, or for one hour in a boiling water bath. The results are given in Table 1. The temperature had little effect upon the absorption by some soils, but it had a very decided effect upon absorption by others. With soil 1595 there is little effect, but with soils 1577 and 1581 considerable in- creases of fixation take place when the temperature rises. Table 1.—Efl‘ect of temperature on percentage of phosphoric acid absorbed. t Room Lab. In ice temper- _ Water One hour No. water ature bath in boiling 31 degrees 40 degrees water 1577 San Antonio Clav Loam. 1”— 6" 50.4 57.2 66.9 85.5 1581 Houston Black Clay Loam 6"—12” 34.6 40.9 48.4 . 60.5 1584 Willis Sand 1”— 6" 9.6 16.9 20.1 15.3 1585 Willis Sand 6”—12” 9.2 15.3 16.1 16.9 1591 Lufkin Sand 1"- 8" 1.6 2.8 3.6 4.8 1595 Austin Clay 1"— 6" 63.7 65.7 66.1 67.7 EFFECT OF TIME The effect of time upon the absorption of phosphoric acid by soils was studied, using the method given above, but allowing the solution to stand at room temperature for 5 hours, 24 hours, 48 hours, 5 days, and 10 days. The only variable condition Was the time. The results of this experiment are given in Table 2. The absorption of phosphoric acid increases with the time of contact. Greater differences appear in the soils after five hours’ contact than after ten days’ contact. There is a tendency towards more complete absorption as the time of con- tact increases. This is not surprising, for the amount of phosphoric acid added to the soil is small, and there should be an abundance of THE FIXATION or PHOSPHORIC A011) BY THE SoIL. '7' fixing material to completely take up all this phosphoric acid, if suffi- cient time is allowed. Table 2.——Effect of time on percentage 0f phosphoric acid absorbed. 5 l 10 Lab. 5 24 48 N0. Hours Hours Hours Days ‘ Days 1577 . . . . . . . . . . . . . . . . . . . . . . .. 55.6 56.3 59.5 72.2 75.4 1586 . . . . . . . . . . . . . . . . . . . . . . .. 21.5 30 39.6 55.6 65.9 1588 . . . . . . . . . . . . . . . . . . . . . . .. 10.3 . . . . . . . . .. 23 0 42.1 42.9 1593 . . . . . . . . . . . . . . . . . . . . . . .. 53.1 55. 64 80.1 80.9 1595 . . . . . . . . . . . . . . . . . . . . . . .. 15.1 22.2 29 6 60.3 72.2 1597 . . . . . . . . . . . . . . . . . . . . . . .. 29.3 34 60.3 61.1 EFFECT OF SALT Table 3 shows the effect of two grams salt used to coagulate the clay. The salt had little effect upon fixation but its use was not adopted for the work described in this Bulletin. The use of the salt aided in clarifying the solution for analytical work and it would probably be well to use a coagulant like this. Table 3.-—-Effect of salt upon the percentage of phosphoric acid absorbed. With Without Laboratory No. NaCl NaCl 1295 . . . . . . . . . . . . . . . . 77. 6 72. 0 1296 . . . . . . . . . . . . . . . . 94. 4 91 .2 1297 . . . . . . . . . . . . . . . . 68.8 63.6 1298 . . . . . . . . . . . . . . . . 69. 6 61 .2 1301 . . . . . . . . . . . . . . . . 12.4 11 .2 1302 . . . . . . . . . . . . . . . . 93.6 90.0 EFFECT OF ACID UPON FIXATION It was shown in Bulletin 126 that treatment with acid may remove part but not all of the fixing power of the soil for phosphoric acid. In order to study this further, two portions of 50 grams of the soil’ each were weighed out, and one portion was treated with 50 c.c. water‘ and 20 c.c. concentrated hydrochloric acid, stirred Well and allowed to stand. The acid was decanted through a filter, and the treatment‘ repeated until all of the calcium carbonate had been decomposed. The- soil was then washed with water and allowed to dry. The original soil, and the soils treated with acid were tested at the same time and under the same conditions for absorption of phosphoric acid by the method previously described. The results of this work are given in Table 4:. The treatment with: acid, which should remove all carbonate of lime, varies in its effect upon the different soils. It decreases the fixation of some soils de- cidedly, while it has little or no effect upon that of others. Soils with high fixation, such as numbers 823, 853, and 873, are especially liable to have their fixation little affected by washing with acid. This fact was also pointed out in Bulletin 126, 1n connection witha\ 8 TEXAS AGRICULTURAL EXPERIMENT STATION. the estimation of active phosphoric acid removed from the soil. As pointed out in that Bulletin, soils with a fixing power exceeding 80 per cent., by the method described above, may give up to the acid used for estimation of active phosphoric acid only a small proportion of the phosphoric acid really soluble in the solvent, on account of wit - drawing by fixation. The treatment with the acid reduces the fixing power of some of the soils to a considerable extent, while the fixing matter requires further study, for so far the study has not led to any clarifying results. Table 4.-—-EiTect 0f extraction with acid upon percentage of phosphoric acid fixed. Original Acid soil treated 91.2 91.2 34.5 31.5 66.0 31.4 52.1 21.7 94.9 89.2 94.8 92.2 67.7 45.0 60.2 33.9 32.5 26.4 71.1 76.6 23.4 19.0 46.3 12.2 71.3 22.5 62.9 10.7 47.7 25.6 50.3 18.5 74.4 25 6 77..4 32 5 EFFECT OF IGNITION It was shown in Bulletin 135 of this Station that ignition affects some phosphates of iron which may occur in the soil, rendering their phosphoric acid decidedly more soluble in acid. It is a question if ignition would not render iron and aluminum compounds in soils more active as regards fixation. Effect of ignition upon the phosphoric acid absorbed by the soil inum dish until all organic matter was destroyed, transferring to a bottle, and treating with potassium phosphate as described in the method for the absorptive power of soils. Another portion of the same soil without ignition was tested at the same time and under the same conditions. _ The results of some of these experiments are given in Tables 5, 6, and '7. The effect of the ignition is to increase the absorption power THE FIXATION on PHosPHoRio A011) BY THE SoiL. 9 of the soil in many cases. This may be due to the heat’s converting part of the carbonate of lime to calcium oxide, which, of course, would unite more readily with phosphoric acid. It is also in part probably due to changes in the character of the iron and aluminum compounds in the soil, caused by the ignition. It has been shown in Bulletin 135 that ignition renders more soluble certain soil phosphates, and causes part of the iron and aluminum oxides to become more soluble in acids. Table 5.-—Effect of ignition of soil upon percentage of phosphoric acid fixed. Laboratory No. Original Ignited 821 . . . . . . . . . . . . . . .. 28.8 35.4 822 . . . . . . . . . . . . . . .. 16.2 32.3 832 . . . . . . . . . . . . . . .. 82.3 80.7 834 . . . . . . . . . . . . . . .. 53.1 67.7 828 . . . . . . . . . . . . . . .. 4.2 19.3 335 . . . . . . . . . . . . . . .. 87.9 90.4 337 . . . . . . . . . . . . . . .. 89.9 89.4 341 . . . . . . . . . . . . . . .. 98.5 91 0 309 . . . . . . . . . . . . . . .. 78.3 97.0 333 . . . . . . . . . . . . . . .. 94.5 98.5 823 . . . . . . . . . . . . . . .. 98.4 93 2 831 . . . . . . . . . . . . . . .. 67.2 99.0 851 . . . . . . . . . . . . . . .. 41.5 68.7 348 . . . . . . . . . . . . . . .. 6.7 5 6 818 . . . . . . . . . . . . . . .. 21.7 43 7 932 . . . . . . . . . . . . . . .. 46.8 98.5 933 . . . . . . . . . . . . . . .. 67.0 98.6 940 . . . . . . . . . . . . . . .. 58.6 69.5 963 . . . . . . . . . . . . . . .. 68.4 99 8 968 . . . . . . . . . . . . . . .. 73.7 81.3 992 . . . . . . . . . . . . . . .. 62.7 64.6 1078 . . . . . . . . . . . . . . .. 31.1 73.7 Table 6.——Effect of treatment with acid and ignition upon percentage of phosphoric acid absorbed Treated Laboratory Number Original Ignited Treated acidz then direct acid ignited 1593 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 56.4 86.8 32.8 81.9 1594 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 68.1 99.0 37.5 53.4 1597 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31.9 98.8 6.9 16.2 1590 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 .3 63.6 1931 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18.5 23 8 1.5 11.8 1586 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 20.8 34 4 0 \ 30.2 1587 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54.2 73.4 26.1 68.7 1588 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10.4 14.6 4.7 19.3 1589 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 50.8 51.8 3.5 41.5 1590 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 73.8 74.4 . . . . . . . . . . . . . . . . . . .. 1580 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 52.1 99.0 24.7 88.1 1582 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 63.9 97 9 38.7 93.0 1585 . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . .. 13.4 28 7 6.7 15.5 1925 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 40.2 71.4 23.6 44.2 1927 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 42.7 86.0 0 38.2 1928 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 49.7 52.3 5.0 43.7 1930 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 47.2 69.8 35.7 98.2 1932 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 34.2 46 2 15.6 37.2 1933 . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . .. 76.8 85.9 52.5 78.8 1934 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 67.2 58.6 47 O 69.2 1935 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 68.7 77.3 38 4 85.4 10 TEXAS AGRICULTURAL EXPERIMENT STATION. ‘Table 7 .—-Efl'ect of treatment with acid and ignition upon percentage of phosphoric acid absorbed. Ignited and Laboratory Number. Not Treated then treated treated 3 1/3N 3 1 3 HCl N. acid 1585 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18.5 3.4 7.3 1588 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10.7 0 12.2 1579 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 7.8 4.4 6.3 1580 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 53.7 19.0 34.6 1933 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 62.5 22.0 40.0 1934 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 51.5 17.5 25.5 1935 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 52.0 0 45.0 1936 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59.5 17.0 31.0 1927 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 44.0 0.5 27.0 1930 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5.3 8.0 17.5 1594 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 66.0 15.0 36.0 1925 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 35.0 15.0 25.5 In order to test this matter further, samples of the soil were weighed out, treated with acid, and ignited. In experiment 762, the sample was first washed with acid, and then ignited, while in experiment 765 the sample was first ignited and then washed with the acid. The re- sults of this work are given in Tables 6 and '7. The eifect of the treatment with acid alone is to reduce the phosphoric acid absorbed. The phosphoric acid absorbed is greater for the soils ignited and treated with acid than for the soils treated with acid and not ignited. ‘This increase occurs When the soil is first treated with the acid and then ignited, or when first ignited and then treated with acid. This shows that the effect of the ignition is to change the iron and alu- minum compounds so that they absorb the phosphoric acid to a greater extent. FIXATION BY MINERALS A study of the fixation of phosphoric acid by minerals which might occur in the soil should throw some light upon the part which such minerals take in the process. Accordingly, a number of minerals were secured, ground finely, and treated with phosphate by the method al- ready described for soils, with the exception that 20 grams of minerals were used in place of 50 grams of soil. Two or more samples of some minerals were secured of different origin. The results are given in Table 8. THE FIXATION or PHOSPHORIO Acrn BY THE SoIL. 11 Table 8.—Percentage of added phosphoric acid fixed by minerals (20 grams to 20mg). Sample Sample Sample N0. 1 No. 2 No. 3 Prehenite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1 24.2 . . . . . . . . . . . . Siderite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77.8 45. 6 37.7 Haematite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22. 6 13.7 36.4 Limonite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 39.9 45.5 Natrolite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.9 12.1 . . . . . . . . . . . . Goethite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.8 27.6 . . . . . . . . . . . . Chrysolite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ._ . . . . . . 17. 8 . . . . . . . . . . . . . . . . . . . . . . . . Nephelite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ' 7.0 . . . . . . . . . . . . . . . . . . . . . . . . Wernerite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 25.7 . . . . . . . . . . . . Stilbite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 . . . . . . . . . . . . . . . . . . . . . . . . Labradorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35. 8 . . . . . . . . . . . . . . . . . . . . . . . . Dewelite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 60.3 16.4 41 7 Wollastonite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39.5 47.1 . . . . . . . . . . . . Serpentine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85.3 . . . . . . . . . . . . . . . . . . . . . . . . pidote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. 7 . . . . . . . . . . . . . . . . . . . . . . . . Biotite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 36.6 31 1 35 0 Kaolinite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28.8 . . . . . . . . . . . . . . . . . . . . . . . . c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. 8 . . . . . . . . . . . . . . . . . . . . . . . . Serpentine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48.8 . . . . . . . . . . . . . . . . . . . . . . . . Phillipsite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36.8 . . . . . . . . . . . . . . . . . . . . . . . . Carbonate of Lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66.0 48.5 . . . . . . . . . . . . Prochlorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 . . . . . . . . . . . . . . . . . . . . . . . . Amphibole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.9 . . . . . . . . . . . . . . . . . . . . . . . . Tremolite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20. 6 . . . . . . . . . . . . . . . . . . . . . . . . None of the minerals examined showed as high a fixing power as some of the soils. The highest is 77.8 per cent. with one sample of siderite. While 20 grams of the mineral were used, and 50 grams soil, yet none of the soils would hardly be likely t0 contain more than this quantity of the mineral. It would appear that some soils contain mineral of much higher fixing power than any of the minerals examined. This difference may be due in large part to the physical character of the mineral in the soil; the soil minerals may be more hydrated, and less compact, than the minerals found in deposits. All the minerals examined showed some fixation, but the fixation with so-me is slight and may be due to physical causes. FIXATION OF PHOSPHORIC ACID OF FERTILIZERS The available phosphoric acid of fertilizers is considered to be pres- ent as mono-calcium phosphate, which is soluble in water, and as dicalcium phosphate, which is only slightly soluble in water, but read- ily taken up by plant roots. When the fertilizer is placed in the soil the mono-calcium phosphate is slowly dissolved by the soil moisture, and partly taken up by plant roots and partly fixed by the soil. This process does not take place rapidly. Let us leave out the action of the plant roots, and consider what occurs in the soil alone. Each lump of fertilizer becomes a center from which the soil moisture dissolves the phosphate. When the solution leaves the lumps of fertilizer, it comes in contact with soil particles, and part of the phosphoric acid is fixed. The amount which is fixed depends upon the strength of the solution, and on the fixing power of the soil particles. The fixing power of the soil particles nearest the lump of phosphate may become completely saturated, while the par- 12 TEXAS AGRICULTURAL EXPERIMENT STATION. ticles further away fix less and less, because the strength of the solu- tion decreases, by fixation, the further it passes from the phosphate. Finally no further fixation occurs, and the solution represents the original soil moisture. Under these conditions there is a lump of acid phosphate, surroundedby a comparatively strong solution of phosphate, which decreases in strength as the distance from the phosphate increases. The size of the area of strong phosphate solution depends greatly upon the fixing power of the soil and the amount of moisture present. Sur- rounding the lump of acid phosphate would be soil particles whose fixing power for phosphoric acid is completely saturated, and around this a zone of gradually decreased fixation. This condition would not be permanent but might be slow to dis- appear entirely. The lump of phosphate would finally lose all its sol- uble material, and finally the remaining rock phosphate might become less soluble than the fixed phosphate surrounding it. The fixed phos- phate nearest the fertilizer would probably be more soluble in soil moisture than that in the remainder of the soil. It therefore would again dissolve slowly, and pass on to zones of greaterfixation, and this process would continue until the solubility of the soil phosphates would become nearly uniform, and the added phosphate distributed through the soil. The nature of the fixing substances in the soil would have an effect upon the soil fertility. Some fixing particles no doubt hold the phos- phoric acid more loosely than do others, so that some give up their phosphoric acid more readily to plant roots than others. The relative predominance of these two classes of fixing particles would affect the rapidity with which the fertilizer phosphate becomes unavailable to plants. This would be one explanation why acid phosphate is more available in some soils than in others. It might be found, for example, that a soil with high fixing power for phosphoric acid but low in car- bonate of lime might receive benefit from lime on account of its help- ing to hold the phosphoric acid in more available forms. The car- bonate of lime particles might change the phosphates to phosphate of lime, and influence the soil favorably in this respect. PERCOLATION AND FIXATION In order to test further the effect of the soil upon acid phosphate, 850 grams of soil were placed in galvanized iron tubes about 14 inches long and 2 inches in inside diameter, having a piece of cloth tied over the lower end. One gram acid phosphate was mixed with the top three inches of the soil, and 100 c.c. water added. The mixture was allowed to stand 24 hours, and then percolated with water until 1000 c.c. had collected. The time required for this varied considerably from 3 hours to 4 days. With some of the soils, successive percolations were made. Table 9 contains the results of this experiment on soils having an absorptive power for phosphoric acid, by the method already de- scribed, of more than 50 per cent. The amount of phosphoric acid in the first percolate averaged 0.4 mg. in 1000 c.c., or 0.4 parts per THE FIXATION or PHOSPHORIC Aorn BY THE S0111. 13 million. The fixation of phosphoric acid by the column of soil was thus almost complete. Table 9.—Mil1igrams of phosphoric acid in 1000 c.c percolate from soils plus acid phosphate Mg. Absorption phosphoric power for Laboratory Number acid in IJhOSDhOTIC, percolate per cent 855 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.2 80 1067 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 92 1122 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 97 1124 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 75 1126 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.4 78 1138 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 98 932 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0. 7 64 960 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 67 1140 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 51 1145 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O. 3 54 1136 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.2 52 Average . . . . . . . . . . . . . . . . . . . . . . . 0.4 A series of experiments with soils having an absorptive power less than 50 is given in Table 10. As the untreated soils in these experi- ments gave up more phosphoric acid to Water than the soils listed in Table 9, experiments were made on these soils both with and without additions of acid phosphate. It is seen from the table that consider- able amounts of phosphoric acid were dissolved by the percolating water and carried down through the soil. Table 10.—Mg. phosphoric acid percolated from soils with and without acid phosphate. No addition Acid phosphate Total Phos~ three phoric Laboratory First Second Third First Second Third perco- acid Number perco- perco- perco- perco- perco- perco- lations absorbed late late late late late late 318 . . . . . . . . . .. 2.4 1.3 0.9 46.2 7.6 6.9 60.7 8.3 936 . . . . . . . . . .. 19.8 5.9 3.1 93.1 12.0 10.3 115.4 5.3 172 . . . . . . . . . .. 3.4 1.9 1.3 50.4 17.1 5.2 72 7 9.6 828 . . . . . . . . . .. 3.5 1.3 1.1 77.6 21.0 9.4 108 0 5.8 860 . . . . . . . . . .. 1.7 0.7 0.9 82.2 19.3 8.4 109 9 8.0 897 . . . . . . . . . .. 3.9 2.9 1.7 42.6 . . . . . . . . . . . . . . .. 42.6 9.0 937 . . . . . . . . . .. 1.1 1.1 0.9 39.5 16.1 9.4 65.0 10.0 1134 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29.0 16.8 13.2 59.0 5.6 1056 . . . . . . . . . .. 7.6 3.5 2.5 99.1 5.2 4.8 109.1 5.4 AverageA 5.7 2.3 1.5 62.2 14.8 8.5 82.5 7.5 314 . . . . . . . . . .. 2.1V 0.5 0.8 50.7 12.8 4.6 68.1 14.6 913 . . . . . . . . . .. 1.1 0.7 0.4 48.2 14.6 6.6 69.4 14.9 174 . . . . . . . . . .. 1.4 0.5 0.6 53.7 14.4 7.1 75 2 10.4 895 . . . . . . . . . .. 2.0 1.9 1.4 21.2 24.1 0.1 45 4 18.0 AverageB 1.6 0.9 0.8 43.5 16.5 4.6 64.5 14.2 180 . . . . . . . . . .. 1.0 0.4 0.1 25.0 5.8 3.8 34.6 22.5 818 . . . . . . . . . .. 1.3 1.0 0.9 13.0 7.0 7.6 27.6 27.3 306 . . . . . . . . . .. 1.0 0.3 0.3 22.5 11.9 1.8 36.2 28.9 894 . . . . . . . . . .. 5.2 3.0 1.8 38.7 23.2 9.8 71 7 29.2 131 . . . . . . . . . .. 3.3 0.3 0.3 52.4 20.5 5.4 78 3 21.1 346 . . . . . . . . . .. 0.7 0.5 0.4 21.4 7.3 4.3 33.0 25.8 896 . . . . . . . . . .. 3.6 2.6 2.0 16.1 12.5 10.1 38.7 21.0 1120 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4.1 10.6 8.8 23.5 28.0 1283 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3.3 6.7 8.3 18.3 30.0 AveragcC.... 2.3 1.2 0.7 21.7 11.7 6.7 40.2 25.9 826 . . . . . . . . . .. 0.6 0.3 0.3 22.2 6.0 4.3 32.5 37.4 126 . . . . . . . . . .. 1.0 0.8 0.3 10.4 8.8 6.2 25.4 42.4 Average D.... 0.8 0.6 0.3 16.3 .4 5.3 29.0 39.9 \ 14 TEXAS AGRICULTURAL EXPERIMENT STATION. This experiment showed the possibility of the loss of phosphoric acid from the soils having 10w fixing power, when heavy rains follow applications of fertilizer. On the other hand, it must be remembered that the subsoil usually has a higher fixing power than the surface soils, so that the phosphoric acid carried down from the surface soil may be held by the subsoil. But the possibility of the loss of phos- phoric acid from fertilizers must be considered in connection with the composition and characteristics of soils. That a greater loss of soil phosphoric acid by percolating water takes place from soils of low fixing power, is also shown in this table. The loss from a soil with low fixing power may be six times that from a soil with a high fixing power. As stated above, when the possibility of loss in this way is considered both the surface and the subsoil must be taken into consideration. Table 11 shows the effect of several percolations upon soils with low fixing power. The time during which the acid phosphate is in contact with moist soil has an effect upon the possibility of loss. This was studied with two soils. The results are given in Table 12. In this experiment the acid phosphate was mixed with the soil as de- scribed above, 100 c.c. water added, and then the percolation was be- gun after 24 hours with one set, after 48 hours with the second set, and five days with the third set, and ten days with the fourth. The amount of phosphoric acid extracted decreased decidedly with the time of contact before the percolation took place. There are still considerable amounts of water-soluble phosphoric acid in the soil,—- evidence that the phosphoric acid is soluble, and further evidence of the possibility of its being taken up easily by plants. It appears probable that the phosphoric acid of fertilizers applied in water-sol- uble form upon soils with low fixing power, may be easily taken up by plants, and may be partly washed from soils by rain. Table 11.—Milligrams phosphoric acid in successive percolates. 896 896 1120 1 134 1283 No Acid Acid Acid Acid addition phosphate phosphate phosphate phosphate First percolate 1000 c.c . . . . . . . . .. 3 6 16.1 4. 1 29.0 3.3 Second percolate . . . . . . . . . . . . . . . . 2.6 12.5 10.6 16.8 6.7 Third percolate . . . . . . . . . . . . . . . .. 2.0 10.1 8.8 13.2 8.3 Fourth percolate . . . . . . . . . . . . . . . . 1.1 6.6 5. 5 8. 5 3.7 Fifth percolate . . . . . . . . . . . . . . . . . . 0.9 4.2 1.5 6.0 4.3 Sixth percolate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 2.3 Seventh percolate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 2.3 Eighth percolate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 2.0 Ninth percolate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 . 7 1 . 8 Tenth percolate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. 5 1.8 Eleventh percolate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 . . . . . . . . . . Twelfth percolate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. 7 . . . . . . . . . . Total . . . . . . . . . . . . . . . . . . .. 11.2 49.5 30.5 96.2 36.5 Absor tion ower for phosphoric agid, pei‘) cent . . . . . . . . . . . . . .. 21.0 . . . . . . . . .. 28.0 5 6 30.0 THE FIXATION 6F PHOSPHORIO A011) BY THE SoiL. 15 Table 12.——Milligrams phosphoric acid in percolates—eifect of time. 1134 896 First percolation after 24 hours. . . 28.0 . . . . . . . . . . . . . . . . . . 28.1 . . . . . . . . . . . . . . . . . . First percolation after 48 hours. . . . . . . . . . 24. 7 . . . . . . . . . . . . . . . . . . 22. 4 . . . . . . . . . . . . First percolation after 5 days . . . . . . . . . . . . . . . . . 10.8 . . . . . . . . . . . . . . . . . . 8.4 . . . . . . First percolation after 10 days. . . . . . . . . . . . . . . . . . . . . . 7.9 . . . . . . . . . . . . . . . . . . 12.0 ‘ Second percolation . . . . . . . . . . . . . .. 5.8 13.1 11.6 6.4 14.9 15.4 12.2 5.1 Third percolation . . . . . . . . . . . . . . .. 10.8 10.6 8.0 8.8 12.5 11.6 8.3 4.6 Fourth percolation . . . . . . . . . . . . . .. 10.2 9.6 6.0 5.8 8.9 9.6 7.5 4.4 Fifth percolation . . . . . . . . . . . . . . .. 6.3 6.4 5.4 4.3 6.6 6.9 6.5 5.6 Sixth percolation . . . . . . . . . . . . . . .. 6.1 5.5 6.8 4.1 . . . . .. 5.6 6.1 5.1 Seventh percolation . . . . . . . . . . . . . . . . . . . . 3.6 6.4 5.4 4.4 4.8 5. 5 4.6 Eighth percolation . . . . . . . . . . . . . . . . . . . . . 2.1 5.9 3.7 5.0 4.6 4. 7 . . . . . . Ninth percolation . . . . . . . . . . . . . . . . . . . .. 3.7 4.1 4.0 4.3 4.3 4.8 . . . . .. Tenth percolation . . . . . . . . . . . . . . . . . . . .. 3.6 3.3 3.4 3.8 3.8 3.8 . . . . .. Total . . . . . . . . . . . . . . . . . . . . .. 77.2 82.9 68.3 53.8 88.5 89.0 67.8 41.4 Fixing power of salt . . . . . . . . . . . . . 5. 6 . . . . . . . . . . . . . . . . . . 21 .1 . . . . . . . . . . . . . . . . . . It is possible that it would be best to supply phosphoric acid to soils With low fixing power in forms that are not readily soluble in water, but easily taken up by plants. This is especially to be con- sidered when heavy rains are liable to occur, which would cause con- siderable amounts of water to pass through the soil. With moderate amounts of rain, the phosphoric acid would be dissolved, but it would remain in the soil. There is also a possibility that it would be best to apply available phosphates in forms not readily soluble in water to soils with a very high fixing power, especially if there are indi- cations that the phosphoric acid fixed by such soils is not available to plants. If applied in a form not soluble in water, it would remain for a longer time in a condition available to plants, provided that it is available in the first place. The question of the effects of fixation upon the availability of acid phosphate and other fertilizers requires further study. The fixation of the water-soluble phosphoric acid of the acid phos- phate takes place partly in the soil immediately in contact with the phos- phates, and partly from the solution as it passes through the soil. As explained above, the solution should be more concentrated next to the particles of soluble phosphate, and should become less concen- trated as it passes away from these particles and comes in contact with the fixing particles of the soil. The solution would decrease progressively in concentration as it passes down through the soil, until the condition of equilibrium is reached between the solubility of the phosphate of the soil and the fixing power of the soil. In order to study this phase of the matter, three percolators were prepared for each soil, the first containing 850 grams of soil but no addition, the second containing 850 grams soil, with one gram acid phosphate mixed with the top 150 grams, and the third containing a mixture of one gram acid phosphate and 150 grams soil. The dif- ference between the phosphoric acid in the percolate from the first and the second percolations represents the effect of the acid phosphate on the entire soil column, while the difference between the phosphoric acid in the percolates from the second and the third percolations rep- 16 TEXAS AGRICULTURAL EXPERIMENT STATION. ‘resents the phosphoric acid withdrawn by the column of 700 grams of soil. These results are given in Table 13. Table 13.—Effect of column of soil on mg. phosphoric acid in percolate. 850 gm. 150 gm. Lab. 850 gm. S011 soil Fixing No. s01] and and power of phosphate phosphate soil 1809 First 1000 c.c., mg . . . . . . . . . . . . . . . . . . .. 0.6 0.5 39.5 53.1 Second 1000 c.c . . . . . . . . . . . . . . . . . . . . .. 0.4 1.3 18.3 . . . . . . . . . . Total . . . . . . . . . . . . . . . . . . . . . . . . . .. 1.0 1.8 57.8 Caught by 700 grams of soil . . . . . . . . . . . . . . . . . . . . . . . . . . . 56.0 1931 First 1000 c.c., mg . . . . . . . . . . . . . . . . . . . . 2.0 22.7 64.7 27.5 Second 1000 c.c . . . . . . . . . . . . . . . . . . . . .. 0.7 9.1 ' 11.7 . . . . . . . . .. Total . . . . . . . . . . . . . . . . . . . . . . . . . .. 2.7 31.8 76.4 Caught by 700 grams soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44. 6 1577 First 1000 c.c., mg . . . . . . . . . . . . . . . . . . .. 0.5 0.4 13.5 . . . . . . . . .. Second 1000 c.c . . . . . . . . . . . . . . . . . . . . . . 0.2 0.9 12.7 56.7 Total . . . . . . . . . . . . . . . . . . . . . . . . . .. 0.7 1.3 26.2 Caught by 700 grams soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24. 9 1932 First 1000 c.c., mg . . . . . . . . . . . . . . . . . . .. 0.8 19.2 60.5 29.2 Second 1000 c.c., mg . . . . . . . . . . . . . . . . . . 0.3 8.7 12.4 . . . . . . . . . . Total . . . . . . . . . . . . . . . . . . . . . . . . . .. 1.1 27.9 72.9 Caught by 700 grams soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45. 0 1592 First 1000 c.c., mg . . . . . . . . . . . . . . . . . . . . 0.0 17.4 55.8 2.9 \ Second 1000 c.c., mg . . . . . . . . . . . . . . . . .. 0.3 12.9 0.0 . . . . . . . . . . Total . . . . . . . . . . . . . . . . . . . . . . . . . .. 0.3 30.3 55.8 Caught by 700 grams soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25. 5 1586 First 1000 c.c.. mg . . . . . . . . . . . . . . . . . . .. x 14.4 51.1 . . . . . . . . .. Second 1000 c.c., mg . . . . . . . . . . . . . . . . . . x x 10.3 . . . . . . . . .. Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14.4 61.4 Caught by 700 grams soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47. 0 x——Evaporated as fast as it came through. It is plain from the results given in the table that the column of 700 grams of soil has a great effect upon the amount of phosphoric acid taken from the soil. These results should be expected. Soil 1592 has a very low fixing power, but it still withholds a considerable pro- portion of the acid phosphate added. It is evident from these figures that a large part of the absorption occurs in the column of soil below the fertilizer, and that the fer- tilizer passes into solution and then is taken up when this solution comes in contact with the soil particles. The rate of this change de- pends upon the water present in the soil, the fixing power of the soil, the amount of rainfall after the fertilizer is applied, and other con- ditions. There is likely to be little loss when the soil has a fixing power of more than 50 per cent. If acid phosphate is applied. at the rate of 1 gram to 850 grams of soil, as in these experiments, it would require an application of 2300 pounds to the acre, to equal the amount used in the experiments, THE FIXATION OF Prrosrnomo A011) BY THE SoIL. I7 . if mixed With all the surface soil to a depth of 7 inches, but since the i acid phosphate could not be mixed with the entire top inch of the soil, but would be either put in the furrow or applied more or less lumpily, a much smaller application would correspond to this proportion. The conditions of the experiment might be paralleled by the appli- . cation of 100 to 200 pounds acid phosphate applied in a furrow. The amount of rainfall required to duplicate the conditions of the I experiment would be very large. Calculated on the area of the tubes used, a percolation of 20 inches rainfall through 12 inches soil would approximately equal the percolation of 1000 c.c. water under the con- ditions of the experiment. This would remove on an average about 60 per cent. of the water-soluble phosphoric acid, if all the rain should fall within 24 hours of the application. A percolation of 20 inches - is out of the question. Rain sufficient to cause a percolation of 4 inches might occur; this would mean a total rainfall of much more than 4 inches, since the ground must become saturated before any a percolation takes place. A sandy soil about 14 inches deep with a saturation capacity of 30 per cent. would require about 5 inches of water to saturate it to the depth of 13% inches, if the soil were dry to begin with. Some rain would run off on the surface. If the soil were half saturated, rain of 3% inches would be needed for 1 inch percolation if no run-off occurred. A heavy rain of 3 or 4 inches within ten days of the application might cause some percolation, and a loss of 3 or 4 per cent. of the water-soluble phosphoric acid added to light sandy soils with sandy subsoils. There is likely to be little loss when the fixing power ex- ceeds 50 per cent. RELATION OF FIXING POWER TO COMPOSITION The fixing power of 761 surface soils and 651 subsoils for phos- phoric acid was determined by the method already described. The soils studied were divided into surface soils and subsoils, and the analyses arranged into groups according to the percentage of phosphoric acid fixed by the soil. The average results of these tabu- lations are given in Tables 14 and 15. An examination of these tables shows that the active phosphoric acid in both surface and sub- soils increases until the absorption is 40 to 60 per cent., and then decreases. The acid consumed increases until the absorption is 60 to 80 per cent. in both tables, and then decreases. The lime increases in the same way as the acid consumed. 18 TEXAS AGRICULTURAL EXPERIMENT STATION. - Table 14.—-Surface soils—table of averages—fixation phosphoric acid. "D c: T3...» -o-» a w-U LJU m o v n3 v i: z: z: r: i a9 0 e _ a’? 5%? "553 3% 3% ‘£5’ 52a a3 in.“ <2; so g5; $9.35 =§ 05g s g 3 n. n. o. mg Z a 5;, g g Q-a Group 0- 20 P205 absorbed... . . 12.92 41.0 3.33 21y .11 1.66 151 Group 20- 4O P205 absorbed . . . . . . 30.85 75.4 11.36 .93 .23 3.86 212 27 6 Group 40— 6O P205 absorbed. . .. .. 50.11 100.7 22.35 1.81 .43 6.96 189 24 7 Group 60—- 80 P205 absorbed. . . . .. 69.41 84.9 48.07 5.34 .71 9.82 136 7 Group 80-100 P205 absorbed . . . . . . 88.15 58. 9 32. 64 2. 62 .72 13.24 78 I l 766 Table 15.~—Table of averages-subsoils—fixa.tion phosphoric acid. s =» 5 3*; a w: a? as w 5g ~55? 3&3 sg as, gt; egg N 9 N "1 no :- s-O" :- “é <52 <52 s: s22 s3‘ 22>; age o Group 0- 20 P205 absorbed . . . . . . 11.97 43.45 2.83 . 15} .13 1.98 63 9.7 Group 20- 40 P205 absorbed. . .. .. 29.87 38.74 9.53 .62 .20 4.16 88 13.6 Group 40- 60 P209 absorbed. . .. .. 50.75 74. 19 24.32 2.34 .41 7.24 126 19.4 Group 60- 80 P205 absorbed . . . . . . 70.22 53.49 31. 72 3.55 .70 9.97 190 29.7 Group 80-100 P205 absorbed . . . . . . 88.21 19.61 23. 78 3.21 .53 12.73 180 27.6 l l l I ‘*4’ The percentage of iron and aluminum oxides increases with the percentage of phosphoric acid fixed, in both surface and subsoils. There is an average relation between the iron and aluminum com- pounds in the soil, and the amount of phosphoric acid. fixed. The iron and aluminum compounds mentioned are those dissolved by strong hydrochloric acid, according to Hilgard’s method, that is, by heating the soil in a boiling water bath 16 hours with hydrochloric acid 1.115 specific gravity. STATISTICAL RELATIONS The relation between the phosphoric acid absorbed and the amount of iron and aluminum oxides dissolved from the soil by strong acid, was studied by statistical methods. Surface soils and subsoils were studied separately. Table 16 is the correlation table for the surface soils. The correlation table for the subsoils is similar, and is not given. The correlation factor R between the phosphoric acid absorbed and the percentages of iron and aluminum oxides in the surface soils is .774 i .010. THE FIXATION OF PHOSPHORIO A011) BY THE SOIL. Table 16.——Correlation between percentages of iron and aluminum oxides and percentages of phosphoric acid absorbed.‘ mo; E€~Q€$EEEQS£$$££Q§1£S° 111z-19'0z 11131311111111?“ 11°‘ 9'0z-1010z 1111111311" "11111|°‘ 010z-19161 11111:11111:1::1" " 9161-10161 111111131111111" " 061-19181 111111:-11111"11111" C“ 9181-10181 111':1:1":1:11111"1 °‘ 0181-191L1 11311111311" ""°‘"" l‘ 91L1-101L1 11111311111" :“°°‘11]@ 011-19191 11111:311111:11111°‘°‘]‘“ 9191-10191 1111:1:111:::11°‘°‘°‘ 1=° 0191-19191 111111111131"" °°"°‘" 1°“ 9191-10191 "11:11111111"1"|°° 01911-191171 :1 1111:1111"""" 11°‘ |=° 91171-101171 11 11 11:1"1"1" 1"°‘°‘ |°° 01171-19191 1111111111": °‘°°°° 1°°°‘ l: 9181-10191 13111111111" 1°‘ 1""I‘° 0'9I—I9'Zl 111111"1:111:" 1°‘" "|‘° 981-1011 11111:11"" """ ‘F 3" l: 0161-1911 1: 11 11 1111‘°°“"“°"1"“°‘"|§ 9111-10111 111: :111“‘"°‘°‘"1°‘°‘""1 1|: 0111-19101 1 1 1 1 1 1 3“‘""""°‘"°‘""" 3" :3 901-10101 11111111"'11“‘"‘*°"1111°° 0101-1916 1 1 1 1 1 1 1°‘ 1°‘°‘°‘ 1“‘"°‘""" 1 2 916-1016 11 1 1 1 1 1 1"°‘°““""°‘ 1" 1" 1 2 016-1918 : 1 :1 1 :1 1"°"°“““""" 1 1°‘ :1 2 918-1018 1111:" 1 :""°‘°° 1" 1" 1" 11 E: 018-1911. 1" 1-1 :""‘°°‘°°""““‘" 1 1 1 1" § 914-1011. 1 1 1 1 1"°‘""‘*“°"°‘°‘" 1 1 1 1 1 $3, 01L-1919 1 1°“ 1 1"” 1‘°°‘"“°"" 1 1 1 1 g2‘, 919-1019 1 1 1" 1"°°°‘ :"°°‘"""" 1 i" 1 3", 019-199 .111"1°°*°°“‘°‘11°‘11:111§ 919-1019 1 1 1°‘°‘°‘°°°°°°‘°“‘ : 1 1°‘ 1 1 11 gfi 019-19117 1" 1°‘ 1°‘°°"“‘°°‘*°°° 1°‘ 1" 1 1 1 1 Q 9117-10111 1 1 1”°‘<°“‘°°°°"°‘°‘"" 1 1 3 1 1 a 0117-1918 : 1""°°°°°°"“““""°‘ 1" 1 1 1 1 115:; ' 918-1018 :"°°"‘°‘°‘°‘”°‘°°"‘°°‘"" 1 1 1 1 1|§P_ 019-191z 1""‘““°‘°‘°‘°‘°‘°" 1°‘ 1" 1" 1 1" Q2 91z-101z °‘ 1‘°=°“2‘"°‘"°‘" 1 1 1 1"" 3 1 1 Q 02-1911 :'°°°§°°:“° :""" 1 1 1 1"-1 1 1 1 g 911-1011 "£912°°°°“°°°‘" I 1"" t 1 1 1 1 : E 011-1910 “£22‘“°‘ 1 1 1 1°‘ 1" 1 z 1 1 1 1 1|Q 091-0 °““ " ."1111111111|°° °.1311111.111:::11:11o1 T; mesaassesesesssssaae 6 dMLLALAAHALALALLLLAAL F‘ 1 mifififififii$fifi3éfifig£é£ 19 _ 20 TEXAS AGRICULTURAL EXPERIMENT STATION. The correlation factor R between the phosphoric acid absorbed and the iron and aluminum oxides dissolved from the subsoil is .701 i .013. These figures show a close correlation between the phosphoric acid absorbed from the soil and the quantity of iron and aluminum oxides dissolved by the strong acid referred to above. There is evidently a close relation between these two factors. The regression coefficient is 0.15 for surface soils and 0.14 for subsoils. The percentage of phos- phoric acid absorbed multiplied by the regression coefficient gives approx- imately the average percentage of iron and aluminum oxides. The iron and aluminum oxides divided by this factor gives approximately the average absorption. A study was also made of the correlation between the phosphoric acid absorbed and the quantity of lime dissolved by strong hydrochloric acid. The correlation factor R for the surface soils is .098 i .024. The correlation factor R for the subsoils is .060 i026. The correlation factor between the phosphoric acid absorbed by the soil and the amount of lime present is, therefore, very low indeed. The percentage of iron and aluminum compounds in the soil is of much greater influence upon the amount of phosphoric acid absorbed than the percentage of lime compounds. RELATIVE FIXATION BY TEXAS SOILS Tables 14 and 15 also show the numbers of surface and subsoils in each group with different fixation powers. Since 1413 soils were examined, these results should represent fairly well the relative fixing powers of Texas soils. About 10 per cent. of the surface soils, and 28 per cent. of the subsoils, have a fixing power of over 80 per cent. The subsoils have a higher fixing power than the surface soils. RELATION OF FIXATION OF PHOSPI-IORIC ACID TO ACTIVE PHOSPHORIC ACID. The fact was brought out in Bulletin 126 of this Station that the phosphoric acid dissolved from soils by N/ 5 nitric acid did not neces- sarily represent all the phosphoric acid which could be dissolved from the soil by this reagent, but represented the equilibrium between the phosphoric acid dissolved and the phosphoric acid fixed from the solu- tion. Known amounts of phosphoric acid added to the soil were not entirely recovered but the amount recovered depended upon the fixing power of the soil for phosphoric acid. This fixation would interfere with the interpretation of the analysis of soils with high fixing power, since the actual amount of phosphoric acid present would remain un- certain. The uncertainty would be in the direction of the soil’s ap-- pearing poorer than it really is. Further work with pot experiments has so far not permitted a dem- onstration of the effect of fixation upon the results, chiefly for the reason that the number of soils with high fixing power included in the pot experiments is comparatively small. Soils having a fixing power of more than 80 per cent. would be chiefly affected, and as, shown in THE FIXATION OF Prrosrrromc A011) BY THE SoIL. 21 tables these would be about 10 per cent. of Texas surface soils and 27 per cent. o-f subsoils. Not all of these soils would be affected, since some soils of this group have much lower fixing power in acid solution than in neutral. ACKNOWLEDGMENT Mr. S. E. Asbury, J. B. Rather, Herman Lebeson, Charles Buchwald, and other members of the staff, took part in the laboratory and other work involved in this Bulletin. SUMMARY AND CONCLUSIONS This bulletin is the study of the relation of fixation to properties of typical Texas soils, especially as related to the loss of phosphoric acid. from fertilizers, or the estimation of active plant food in the soil. A comparison of fixation at different temperatures showed thatiwith- some soils considerable increases took place when the temperature in-- creased. The fixation of phosphoric acid by the soil increased with the time of contact. The addition of two grams of salt added to precipitate the clay had little effect upon the amount of phosphoric acid fixed. Treatment with acid, which would remove the carbonate of lime, had little effect upon fixation by some soils, while it decreased the fix- ation by other soils considerably. Igniting the soil increased the power of the soil to fix phosphoric acid, even when the lime had been removed by previous treatments with acid. A number of minerals examined for fixation did not have high e-nough fixing power to explain fixation by the soils. The soil minerals have a higher fixing power than the minerals found in deposits. A lump of phosphate in the soil is probably surrounded by a solu- tion decreasing in strength as the distance increases and by zones of soil particles which increase in fixing power, according to the more or less complete satisfaction of their fixing power by the soluble phos- phoric acid. Soils having a fixing power of more than 50 per cent. lost prac- tically no phosphoric acid when treated with acid phosphate and sub- jected to percolation under the conditions described. Soils having a fixing power of less than 5O per cent. lost considerable amounts of fertilizer phosphoric acid by percolation. A large part of the fixation took place in the soil column below the mixture of soil and fertilizer. . The amount of phosphoric acid in the percolate decreased as the tim of contact between the soil and fertilizer increased before water was applied. Heavy rains would be required to cause loss of phosphoric acid even from soils of low fixing power, under natural conditions. A rain of 3 or 4 inches within ten days might cause a loss of 3 or 4 per cent. of the water-soluble phosphoric acid applied to light sandy soils with sandy subsoils, having a fixing power of less than 50 per cent. 22 _ TEXAS AGRICULTURAL EXPERIMENT STATION. An examination of 761 surface soils and 651 subsoils showed that the percentages of iron and aluminum oxides increased as the per- centages of phosphoric acid fixed increased. The correlation factor R between the phosphoric acid absorbed and the percentages of iron and aluminum oxide dissolved from the surface soils was .774 i .010. The correlation factor R for the subsoils was .701 i .013. There was a close correlation between the phosphoric acid fixed by the soils and the quantities of iron and aluminum oxides dissolved by strong acid from the soils. The correlation factor R between the quantity of lime dissolved by strong acid, and the phosphoric acid fixed was .098 i .024 and for the subsoils it was .060 i .026. There was little correlation between the phosphoric acid absorbed by the soil and the amount of lime present. A table is given showing the relative fixation of 1413 Texas soils. Further work is required on the relation between the fixation in the soil and the effect of fixation upon the active phosphoric acid recovered from the soil.