32 THE CDW PEA. 



It acts mechanicalhr, by sending its 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 imprcjvement 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, clovers, alfalfa, vetches and 

 melilotus, all like it belonging to the legume family, pro- 

 duce a similar fertilizing effect. The formerly, but no 

 longer fully accepted, explanation of the fertilizing power 

 of these plants was that their long tap roots bring up plant 

 food from the subsoil, and, on their deca)-, leave it within 

 reach of shallow rooted plants, usually grown after peas. 

 They do, to some fxtent, act in this way, but not sufficient- 

 ly to account for anything like their full effects. This 

 explanation failed to account for the 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, 



