THE COW PEA. 37 



The renovation of soils through the use of cow peas de- 

 pends largely on the use to which they are put. The stubble 

 and roots contain considerable fertilizer, and the nitrogen is 

 mostly gain; but much potash and phosphoric acid are re- 

 moved in the crop taken off, and unless this loss be made 

 good by applications of mineral plant food, cow peas act- 

 ually exhaust the soil. This point is important and needs 

 always be kept clearly in mind. Cow peas, in common with 

 wheat, require plant food, notably potash and phosphoric 

 acid; but wheat requires nitrogen plant food, cow peas do 

 not. The whole difiference between legumes and non- 

 legumes is stated in this one point of feeding. Among 

 legumes, the cow pea stands first and pre-eminent as a crop 

 producer of fertilizer nitrogen. It may be grown between 

 crops of wheat and thus furnish nitrogen for many success- 

 ive crops. 



The soil improvement is well illustrated by an exami- 

 nation of the last foregoing table. A ton of timothy hay 

 contains 25 pounds of nitrogen, 18 pou>nds of potash and 10 

 pounds of phosphoric acid. All this must be supplied by 

 the soil. A ton of cow pea hay contains 40 pounds of 

 nitrogen, 30 pounds of potash, and 10 pounds of phosphoric 

 acid, of which only the latter two need be supplied by the 

 soil. Suppose both are returned to the soil in the shape of 

 farmyard manure; estimating roughly, in the case of timothy, 

 the soil receives back what it gave to the timothy, but in 

 that of the cow pea, it receives not only what it gave, but 40 

 pounds of nitrogen in addition thereto. 



