542 NATURE AND PROPERTIES OF SOILS 



Table CXXIII 



EFFECT OF VARIOUS CROPS ON THE NITRATE NITROGEN OF THE 

 SOIL DURING OCTOBER, 1916-1920. 1 



Green-Manuring Crop 



Rye 



Oats 



Vetch 



Peas 



Rye and vetch 

 Rye and peas. 

 Sod 



Nitrates in the 



Soil in October. 



Eye Taken as 



100 



100 

 73 

 73 

 83 

 74 

 75 

 6 



Percentage Se- 

 duction of 

 Nitrates in 

 October Compared 

 with July 



37 

 44 

 57 

 10 



58 



58 







The intermediate compounds that are formed should yield 

 an organic matter carrying a black pigment, should readily 

 split up into simple compounds, and should be in general 

 beneficial, both directly and indirectly, to plant growth. 

 Plenty of moisture is essential when green-manures are de- 

 caying, not only to hasten the transformation itself but that 

 the normal soil processes may not be interrupted by a lack 

 of water. The caution with which green-manures must be 

 utilized in semi-arid regions arises because of the drying influ- 

 ences of rapid decay and the danger of filling the soil with 

 undecomposed plant residues. Even in humid regions, green- 

 manures may be detrimental if dry weather sets in before a 

 major portion of the decay processes is completed. 



As plant tissue decays in the soil, there seem to be two 

 general groups of forces at work which produce three distinct 

 stages of organic destruction. 2 In the first stage, humus pro- 



1 Unpublished data. Dept. Soils. Cornell University. 



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

 Stages of Growth; Thesis for degree of Doctor of Philosophy, Cornell 

 University, 1919. 



