THE COW PEA. 23 



even when actually needed, a small application suffices. The 

 average farm land is deficient in nitrogen, but when this 

 element is to be supplied in the form of commercial fertil- 

 izer it is better perhaps to apply it to corn, cotton, grain, 

 grass, and other crops, which do not obtain it from the air, 

 rather than to the cow pea, which does so gather it for itself. 

 It appears that, when the cow pea grows on a soil naturally 

 rich and well supplied with nitrogen, the plant becomes 

 "lazy," and draws from the nitrogen already in the soil be- 

 fore exerting its natural and peculiar power of collecting it 

 from the air by means of the little nodules on its roots. Thus 

 every habit and characteristic of the plant shows that the 

 true economy of the cow pea is to restore poor land with 

 the aid of potash and phosphoric acid rather than to de- 

 plete good land and use nitrogen which can be employed to 

 better advantage in producing other crops which need it 

 more. In discussing fertilizer for cow peas, or other 

 crops, no unvarying rule can be formulated. Soils differ so 

 much that a mixture giving good results on one field may 

 fa'l or be wasteful on another. Fields on the same farm, 

 often those lying side by side, differ in their crop re- 

 quirements. One experiment at the Delaware Experiment 

 Station showed that where 160 pounds of muriate of potash 

 were used per acre the yield of cow pea vines was doubled, 

 while phosphoric acid was apparently without effect. Here 

 was a soil naturally strong in phosphoric acid, yet it would 

 not be safe to accept this result as a sure rule for general 

 fertilizing. On most soils of low-producing power, potash 



