174 Journal of Agricultural Research voi. xiii, no. 3 



each thoroughly mixed with 500-gm. portions of the soil. The mixture 

 thus represents an addition of 20 tons of green manurial dry matter to 

 2,000,000 pounds, or an acre 7-inch layer of soil. 



Like mixtures of corresponding amounts of the air-dried manurial 

 substances were used with 500-gm. portions of the soil from Series II. 



SUBSEQUENT TREATMENT 



The mixtures thus prepared were kept in large jars freely exposed to 

 the air and sunshine for two months; thereafter, until the close of the 

 experiment, in a well- ventilated room. The entire period extended from 

 July 7, 1914, to April 7, 1915. The jars were weighed at frequent inter- 

 vals, and the losses of weight made up by the addition of distilled water' 

 so as to keep the soil quite close to the optimum moisture content with 

 which it was started, in order that, as respects the moisture present, the 

 fermentative conditions might be more favorable. 



A control sample of the original untreated soil was similarly kept 

 during this period. 



LIMESTONE-REQUIREMENT DETERMINATIONS 



At periodic intervals the limestone requirements of these mixtures 

 were determined. To obtain samples for this purpose, the entire mass of 

 material was removed from the jar, thoroughly mixed, a sample sufficient 

 for duplicate determinations withdrawn, and the remainder of the soil 

 returned to its jar, and put as nearly as possible into the original condi- 

 tion of compactness. The determinations were made by the Veitch 

 method, the same as for the original soil. 



Unfortunately the determinations were not begun until two weeks 

 after the mixtures were prepared and exposed in moist condition as above 

 described. The changes in limestone requirement during this period 

 of fermentation may, however, be approximated if we assume that in 

 each case it corresponds to the sum of the limestone requirement of the 

 soil and the calcium-carbonate equivalent of the water-soluble acids in 

 the manurial material used — that is, the sum of the limestone require- 

 ment of the soil and the calcium carbonate equivalent of the water- 

 soluble acids in 40,000 pounds of the manurial dry matter, the manurial 

 requirement for 2,000,000 pounds of soil. 



The sum thus obtained must be reduced to the equivalent for 2,000,000 

 pounds of the mixture, because all subsequent determinations are based 

 upon that quantity of the mixtures. 



If the colloidal substances in the plant materials are capable of absorb- 

 ing lime from limewater so as to increase the apparent acidity of the 

 materials, the theoretical limestone requirement thus calculated is, of 

 course, too low. 



