GREEN-MANURES 545 



vestigators 1 as a measure of humification, since a favorable 

 environment for nitrification probably does not occur until 

 the more rapid decomposition processes are completed. In 

 general, the more rapid the decay of the green-manure, the 

 sooner will nitrification be active again. 



Besides affecting the bacterial activity of the soil, the de- 

 caying green-crop influences the solubility of the soil min- 

 erals. Jensen 2 found that the addition of 3 per cent, of 

 green-manure raised the solubility of lime and phosphoric 

 acid 30 to 100 per cent. This was over and above the mineral 

 constituents which came directly from the decomposing green- 

 crop. Magnesium and iron were also markedly influenced. 



314. Crops suitable for green-manures. — An ideal green- 

 manuring crop should possess three characteristics: rapid 

 growth, abundant and succulent tops, and the ability to grow 

 well on poor soils. The more rapid the growth, the greater 

 the chance of economically using such a crop as a means of 

 soil improvement. The higher the moisture content of the 

 crop, the more rapid the decay and the more quickly are bene- 

 fits obtained. As the need of organic matter is especially 

 urgent on poor land, a hardy crop has great advantages. 



The crops that may be utilized as green-manures are usually 



1 Hutchinson, C. M., and Milligan, S., Green-Manuring Experiments, 

 1912 and 1913. India Agr. Ees. Inst. Bui. 40, Pusa, India, 1914. 



Maynard, L. A., The Decomposition of Sweet Clover as a Green- 

 Manure under Greenhouse Conditions; Cornell Agr. Exp. Sta., Bui. No. 

 394, 1917. 



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

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

 University, 1919. 



3 Jensen, C. A., Effect of Decomposing Organic Matter on the Solu- 

 bility of Certain Inorganic Constituents of the Soil; Jour. Agr. Ees., 

 Vol. IX, No. 8, pp. 253-268, May 1917. 



See also, Snyder, H., Humus as a Factor in Soil Fertility; Minn. Agr. 

 Exp. Sta., Bui. 41, 1895; and Production of Humus from Manures; 

 Minn. Agr. Exp. Sta., Bui. 53, 1897. 



Hopkins, C. G., and Aumer, J. P., Potassium from the Soil; 111. Agr. 

 Exp. Sta., Bui. 182, 1915. 



Hopkins, C. G., and Whiting, A. L., Soil Bacteriology and Phosphates; 

 111. Agr. Exp. Sta., Bui. 190, 1916. 



