1^8 Journal of Agricultural Research voi. xin, no. 3 



(3) The properties of the soil itself have no direct causal relation to 

 these changes, since these changes are but slightly if at all manifest in 

 the control soil. The changes are therefore related either to the sub- 

 stances possessed in common by the manures, or to other substances 

 produced by reaction between the plant materials and the constituents 

 of the soil. 



CHANGES OF THE FIRST PERIOD 



This 2-week period immediately succeeding the beginning of the experi- 

 ment shows no change in the limestone requirement of the control soil, 

 but a very marked reduction in that of all the manurial mixtures with 

 the soil. This reduction has been so great as not only to destroy the 

 immediate acid actions of the green manures but also a large part of 

 those which the soil by itself exerts. 



Coville, in his study of the reactions occurring during the formation of 

 leaf mold, has outlined the causes of the changes manifest in that case. 

 The same chain of effects, other than such as are due to leaching, are 

 doubtless to be found in the case of the green manures. 



The alkahne effects so promptly displayed may be accounted for by 

 three well-known fermentative changes: (i) The destruction of the free 

 acids of the green manures, probably by molds; (2) the destruction of a 

 part or all of the combined organic acids, liberating the alkaline sub- 

 stances with which they were combined in the fresh plant material, so 

 that these alkaline materials can aid in turn to satisfy part of the original 

 requirement of the soil; (3) the conversion of the nitrogenous material 

 of the manures to ammonia, which can, like the bases of the organic 

 salts, serve as alkali for the soil. 



No analytical studies suited to determine whether any or all of these 

 causes had actually operated in these experiments were made. We 

 have, however, some indirect evidence upon the subject. 



In the first place, the surfaces of the mixtures were promptly covered 

 with thick felts of white mold. The presence of organisms capable of 

 rapid destruction of the organic acids of the green manures is therefore 

 established. 



In the second place, the degree of the change in limestone requirement 

 and the neutralizing effect possible from the complete ammonification 

 of all the nitrogenous substances of the manures, and that possible from 

 the complete liberation of all the alkaline ash constituents of the manures, 

 may exhibit relations serviceable for this study. These facts are set 

 forth in Table V, the ammonia and alkaline ash figures being expressed 

 in the calcium-carbonate equivalent for 20 tons of dry matter of the 

 respective manures, the proportion mixed with the soil in these experi- 

 ments. 



