GREEN-MANURES 



547 



soil may be used as a rough measure of the rate of decay of 

 green-manures. Admitting such a criterion, certain data from 

 Cornell University become particularly interesting. In a 

 five-year continuous test, green-manuring crops were seeded 

 in July and plowed under in the early part of the succeeding 

 May. The nitrate content of the soil was determined at a 

 number of times during the spring, summer, and fall. A de- 

 crease in nitrates always occurred in the autumn, while an 

 increase began soon after the crops were turned under in the 

 spring. In the following table the rye crop is taken as 100 in 

 both October and July: 



i/£i 



Table CXXIV 



RELATIVE INFLUENCE OF GREEN-MANURES ON THE 

 ACCUMULATION OF SOIL NITRATES. 1 



Green-Manure 



Rye 



Oats 



Veteh 



Peas 



Rye and vetch 

 Rye and peas. 



It is immediately apparent that the succulent rye and vetch 

 that survive the winter give better results, as far as nitrate 

 production is concerned, than the dry and dead oats and peas. 

 This shows clearly the value of succulence and the necessity 

 of turning under a crop partially matured. 2 The advantage 

 of the legumes over the non-legumes is not hard to explain. 



1 Unpublished data. Dept. Soils, Cornell University. 



3 Martin, T. L., The Decomposition of Green Manures at Different 

 Stages of Growth; Thesis for the Degree of Doctor of Philosophy, 

 Cornell University, 1919. 



