38 AGRICULTURE FOR BEGINNERS 



Let us now see how easily plant food may be economized 

 by the rotation of crops. 



If you sow wheat in the autumn, it is ready to be har- 

 vested in June, the very month for planting cowpeas. Plow 

 the wheat stubble under, and sow the same field to cowpeas. 



FIG. 26. COWPEAS AND CORN AUGUST 

 From photograph loaned by Director B. W. Kilgore 



If the wheat crop has exhausted the greater part of the 

 nitrogen of the soil, it makes no difference ; for the cow- 

 pea will get its nitrogen from the air, and not only provide 

 for its own growth, but, in the queer nodules of its roots, 

 will leave quantities of nitrogen for the crops coming after 

 it in the rotation. 



