The Bulletin. 



69 



grains arc 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 



Nodules on Cowpea Roots, where Nitrogen-gathering Bacteria Work. 



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

 under, this amount of nitrogen, corresponding to more than 700 

 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. 



