674 



Journal of Agricultural Research 



Vol. XII, No. lo 



Table I. — Solubility of calcium and phosphate in soil immediately after adding calcium 

 carbonate, tricalcium phosphate, and ammonium sulphate 



Treatment. 



Soil only 



Soil and calcium carbonate 



Soil and tricalcium phosphate 



Soil, tricalcium phosphate, and calcium carbonate. . 



Soil and ammonium sulphate 



Soil, ammonium sulphate, and tricalcium phosphate 



These data show that the addition of calcium carbonate produced no 

 effect on the immediate solubility of the calcium already in the soil or 

 that added as tricalcium phosphate, but the addition of tricalcium phos- 

 phate produced an increase of about 5 p. p. m. of soluble calcium and 

 II. 2 p. p. m. of soluble phosphoric acid. The most notable effect was 

 produced by ammonium sulphate, which caused an increase in water- 

 soluble calcium from 27.5 to 90.1 p. p. m. 



The data submitted in Table I should not be considered as represent- 

 ing true solubility determinations, for it is not certain that equilibrium 

 was completely established, either between the various solids present 

 and the solvent (water), or between the constituents of the soil and the 

 chemical substances that were added to it. A longer period of contact 

 might have yielded extracts either more or less concentrated, depending 

 on whether or not the rate of solution was greater or less than the rate 

 of fixation. The same procedure was followed in making these deter- 

 minations, however, as was used at the close of the incubation periods, 

 and, although the results are not strict solubility determinations, they 

 are believed to be comparable, and that any difference between the 

 amounts of calcium and phosphoric acid found at the beginning and the 

 close of the periods of incubation may be assumed to have arisen mainly 

 through the action of biochemical agents.^ 



After incubation periods of 28, 57, and 157 days, quantities containing 

 200 gm. of dry soil were transferred from the incubation jars to flasks, 

 distilled water was added at the rate of 250 parts per 100 parts of dry 

 soil, was shaken vigorously once every 10 minutes during an hour, and 

 was then filtered through Chamberland-Pasteur filters as in the pre- 

 ceding series. Soluble calcium and phosphoric acid were determined 

 in the filtrates by the methods already referred to, and nitric nitrogen 

 by the phenoldisulphonic-acid method. The filtrates were also tested 

 for nitrite, but not more than 0.5 p. p. m. was found in any case. The 

 average results of closely agreeing duplicates are recorded in Table II. 



*It was not deemed advisable to maiataia separate portions in a sterile condition, owing to the fact 

 that the various methods now in use for bringing about complete sterilization in soils probably affect the 

 solubility of the various constituents. 



