155 



taming the fertility of a soil. They show that while both leguminous 

 and non-leguminous plants enrich the soil alike in humus-forming 

 materials, in proportion to the size of the crop, they differ in respect to 

 the source of their nitrogenous materials. While non-leguminous 

 plants derive their nitrogen supply almost exclusively from the soil, 

 leguminous plants may take theirs largely from the air Conse- 

 quently, if spurry, buckwheat, mustard, etc. (non-leguminous plants), 

 are grown on the soil and the crop ploughed in, the soil is not materi dly 

 enriched in nitrogen ; the process is simply returning to the soil all the 

 nitrogen which the crop took from it. But since leguminous plants 

 may derive the larger propotion of their nitrogen from without the 

 soil — that is, from the air — their use for green manuring actually 

 enriches the soil in nitr genous matter. 



It will thus be seen that by green manuring with leguminous crops 

 it is possible to manure the soil with nitrogen from the air, a free and 

 inexhaustible source, and thus avoid buying fertilisers containing much 

 nitrogen. This greatly lessens the expense for commercial fertilisers, 

 for nitrogen is the most expensive element the farmer has to buy. As 

 stated above, it co-ts from 15 to 20 cents a pound, while potash and 

 phosphoric acid c< st only 5 to 7 cents, or even less. Although grains, 

 grasses, corn, cotton, root crops, tobacco, etc., can not use the nitrogen 

 of the air, green manuring enables them to benefit by it indirectly. 



SOME CROPS FOR GREEN MANURING. 



Among the legumiuous pi >nts more commonly used for green manur- 

 ing in this country and in Europe are cowpea, alfalfa, clovers, melilotus, 

 serradella, lupines, vetch, and horse bean. Some of these are described 

 below. 



Cowpea. 



The cowpea is widely used as a green manure in the Southern States. 

 According to the North Carolina Experiment Station, " the cowpea, 

 being a tender annual, shonld always be sown in the spring. It will 

 give a good yield sown as late as July 1, but the earlier it is sown after 

 danger of frost is passed the heavier the yield. The pea is usually 

 sown broadcast at the rate of 2 bushels p>r acre and ploughed or har- 

 rowed in. The cowpea is not affected by heat, and is less sensitive to 

 drought than any of the clovers." 



Experimen's have shown that cowpeas respond readily to applica- 

 tions of potash and phosphates, and are able to derive their nitrogen 

 very largely from the air. Inasmuch us cowpeas are large gatherers of 

 nitrogen, and also secure considerable amounts of potash and phos- 

 phoric acid through their extensive root system, which reaches down to 

 the subsoil, they have a high fertilising value. How to get the greatest 

 benefit from the fertilising constituents of cowpeas is one of the problems 

 on which the experiment stations are working. If the cowpeas are 

 ploughed under ia the fall and the ground lef )bare until spring a large 

 share of the nitrogen will be leached away. By sowing wheat or rye 

 after the cowpeas are ploughed under part of this loss may be avoided. 

 If the vines are cut and allowed to lie on the ground during the winter 

 the nitrogen is rapidly lost. In an experiment at the station i i Ala- 



