194 Journal of Agricultural Research voi. xiii. No. 3 



II. — THE SOIL WITH STABLE MANURE ADDED 



(4) The original limestone requirement of this mixture was not deter- 

 mined, nor were the data needful for its computation secured. There 

 was, however, an almost continuous increase in this requirement from 

 the end of the second week to the conclusion of the seventh month. 

 During the third and fourth weeks the increase was 678 pounds (in 

 2,000,000), and during the fourth to the seventh month, inclusive, 1,652 

 pounds; but the two following months witnessed a decrease of nearly 

 1 ,000 pounds. 



(5) The nitrates, on the other hand, increased continuously after the 

 fourth week. This increase was greatest during the fourth and fifth 

 months and again -during the eighth and ninth months; at the one time 

 the limestone requirement was increasing, and in the other markedly 

 decreasing. At the utmost of its effect the nitrification can account 

 for but a small fraction of these limestone-requirement changes. 



(6) Until the end of the third month the limestone requirement of 

 the stable manure mixture was less than that of the soil; from the fifth 

 to the seventh month it was 1,000 pounds greater than that of the soil 

 alone; but at the end of the experiment the soil had the greater lime 

 requirement. 



(7) At all times the stable manure mixture shovv'cd more nitrates than 

 the soil alone. 



III. — THE SOIL WITH ADDED FRESH GREEN MANURES 



(8) At the end of the first two weeks the limestone requirement of 

 these mixtures was, on the avearge, about 1,400 pounds less (in 2,000,000) 

 than that of the soil alone. During these two weeks this requirement 

 decreased from 5,858 pounds, the theoretical original acidity of the 

 mixtures, to 3,044 pounds, a decrease of 2,540 pounds, or nearly one-half. 

 As noted earlier in this summary, the soil alone showed no change in this 

 requirement during this period. 



(9) The plan of the experiment was not sufficientl)^ complete to afford 

 a proof of the cause of this decreased limestone requirement. Three 

 factors ma}^ have operated to cause it: A destruction of the free acids 

 of the green manures; a destruction also of the plant acids combined as 

 salts with a consequent liberation of alkaline ash constituents; and the 

 conversion of the organic nitrogen to ammonia. The first factor is too 

 small to account for a large fraction of, the observed decrease. Poten- 

 tially, either of the others would suffice to account for it in most of the 

 cases, though not in all. Complete destruction of the acid combinations 

 in the plants within two weeks, or complete ammonification of the 

 organic nitrogen within two weeks, seems unlikely. It is probable, 

 therefore, that a large development of the three factors at the same time 

 is the real explanation of the observed change. 



An increase of limestone requirement in the case of these mixtures 

 occurred during the third and fourth weeks, and again during the fifth 



