LEGUMES AXD GRASSES 



37 



WHEAT 



UJ 



cr 



8 



tr 



Q. 



• 



go 



q: 

 o 



CD 



Q 



-J 

 UJ 



I I 



CORN 



ALFALFA 



J L 



1911 '15 '20 '25 '30 '35 40 45 '50 



YEAR 



Figube 2. — Regression lines calculated from the annual yields of treated and untreated 

 wheat, corn, and alfalfa when grown continuously on the same land at Manhattan, 

 Kans. From Hobbs (32). 



