THE COW PEA. 37 



plants act mechanically, by sending their long tap roots deep 

 into the subsoil, loosening and making it more porous, and 

 chemically, by collecting and assimilating the free nitrogen 

 of the air and making it available food for future crops. 

 Soil improvement is the chief object for which it is grown 

 in this country. Not that its extensive acreage is due alone 

 to its fertilizing effect, but its value for that purpose is an 

 additional and important reason why it is used in preference 

 to any other hay or forage crop. How to use this reno- 

 vating and fertilizing power to its full and best advantage 

 is a matter of prime importance. 



In strong contrast to the established fact that most 

 other cultivated crops decrease the fertility of the soil, 

 stands the fact that the cow pea increases it. A few other 

 plants, including the beans, field peas, clovers, alfalfa, 

 vetches and melilotus, all like it belonging to the legume 

 family, produce a similar fertilizing effect. The explanation 

 formerly given of the fertilizing power of these plants was 

 that their long tap roots bring up plant food from the 

 subsoil, and, on their decay, leave it within reach of shallow 

 rooted plants, usually grown after peas. This explanation 

 is now known to be incomplete. The plants do, to some 

 extent, act in this way, but not sufficiently to account for 

 anything like their full effects a difference soon recog- 

 nized on soils deficient in nitrogen between the soil effects 

 of legumes and of other deep-rooting plants, in satisfying 

 the demands of the crops which followed. Experiments, 

 undertaken to solve this problem, demonstrated the fact 



