38 The Bulletin. 



roots of the cowpea plant. These nodules are the home of the bac- 

 teria and are shown in the cut on another page. Corn, cotton and the 

 grains are not able to thus get nitrogen from the air, but must be sup- 

 plied with it through fertilizers or from the cowpea and other legu- 

 minous plants, after they have obtained it and used it in their growth 

 and have decayed in the soil. One ton of pea-vine hay contains in 

 round numbers 47 .pounds nitrogen, the greater portion, or all, of 

 which it has obtained from the air, and if left on the soil or when 

 turned under this amount of nitrogen, corresponding to more than 

 600 pounds cotton seed meal, is added to the soil for soil improvement 

 and for the growth of other crops. The yield of pea-vine hay on fair 

 land varies from one to three tons, and the amount of nitrogen thus 

 collected and stored in the soil is seen to be large, and in addition to 

 this must be considered the value of the organic matter in improving 

 the texture and physical condition of the soil. 



The question frequently arises as to whether or not it is best to cut 

 and use the vines for hay or allow them to remain on the soil for its 

 improvement. The feeding value of the hay needs to be considered 

 in this connection, as the feeding value can be obtained, and under 

 the most favorable conditions TO to 80 per cent of the fertilizing value 

 be returned to the soil in the manure. This is seldom accomplished, 

 however, with the methods followed for saving and handling manure. 

 In most cases likely not over 50 per cent and generally much less 

 than this finds its way back to the land. If the improvement of the 

 land is the sole of main question, there can be but one answer, and 

 that is to leave the entire crop on the soil. In addition to the 47 

 pounds of nitrogen there are in a ton of pea-vine hay 10 pounds phos- 

 phoric acid and 29 pounds potash, which would be worth, at the 

 present prices for these three constituents in fertilizers, namely, 18 

 cents per pound for nitrogen, 5 cents per pound each for phosphoric 

 acid and potash, $10.56 per ton. These constituents average around 

 85 per cent of the entire fertilizing value of the pea crop, which is 

 made up of hay, roots and stubble, the roots and stubble containing 

 on an average about 15 per cent of the fertilizer constituents of the 

 cowpea crop. Good crops of cowpeas grown on land and left there 

 will improve it rapidly, but if the hay is removed and exhausting 

 crops are planted in rotation the productiveness of the soil will be 

 but slightly increased or not at all, unless judicious fertilization is 

 followed. 



Turning under large crops of cowpeas in the fall, to be followed by 

 small grain, frequently results in disappointment because of reduced 

 yield in comparison with land which did not have the peas. This is 

 due to the habit of growth of the small grain, which require a com- 

 pact soil. The peas leave the soil too open and porous. This inter- 

 feres with root development and water-holding capacity. If the crop 

 is handled properly this difficulty will not be encountered. On heavy 



