GRBBN-MANUEES 



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 ex^ops 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 alw^ays 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 : 



Tablk CXXIV 



relatrve influence of geeen-manuees on the 

 accumulation op soil nitrates.^ 



Green-Manure 



Nitrates in July, 

 Soil Fallow Since 



Mat 1. 

 Rye Taken as 100 



Eye 



Oats 



Vetch 



Peas 



Rye and vetch 

 Rye and peas. 



100 

 78 



120 

 99 



136 



102 



Nitrates in Oct., 

 Soil Under Crop 



Since July. 

 Eye Taken as 100 



73 

 73 



83 



75 



It is immediately apparent that the succulent rye and vetch 

 that survive the winter give better result., 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.^ The advantage 

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



* Unpublished data. Dept. Soils, Cornell University. 



''Martin, T. L., The Decom^sition of Green Manures at Different 

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

 Cornell University, 1919. 



