THE COW PEA. T 7 



must be present and in the proper proportion, otherwise 

 there cannot be a full growth. While cow peas do have 

 the property of drawing nitrogen from the air, a certain 

 amount of this ingredient is required in the soil in which 

 they grow, and must be artificially supplied, if not al- 

 ready present. The cow pea plant begins to take up 

 atmospheric nitrogen when its leaves develop, and on poor 

 soils, before this stage is reached, the young plants gener- 

 ally suffer from the lack of nitrogen. This poverty ot 

 nitrogen is indicated by a yellowish leaf, absence of vigor in 

 the plant and a general sickly appearance ; an application of 

 about 75 pounds of nitrate of soda per acre quickly remedies 

 the trouble. 



While an artificial application of nitrogen is regulated 

 by the circumstances described, there are no such condi- 

 tions affecting potash and phosphoric acid. Experiments 

 at the Louisiana Experiment Station show that one acre of 

 average cow peas contains 65 pounds of nitrogen, in 

 pounds of potash and 20 pounds of phosphoric acid; of 

 this the roots and stubble alone contain 8 pounds of nitro- 

 gen, 1 8 pounds of potash and 5 pounds of phosphoric acid. 

 These figures vary, of course, with different yields, but the 

 range of variation is not wide, and only serves to bring out 

 clearly and boldly the fact that, with every pound of nitro- 

 gen, a certain amount of potash and phosphoric acid is 

 also assimilated by cow peas. These weights do not fix 

 absolutely the amount of plant food needed by cow peas, 

 but they do suggest approximately and relatively what the 



