LEGUMES AND GRASSES 



39 



0.240 



.080' £ ^ (5 20 25 30 35 40 45 



YEARS OF CULTIVATION 



F IGCRE 3.-Effect of cultivation on nitrogen content of surface *«|H« Colby, 

 and Garden City, Kans., 1916-16. Data from Hobbs and Bro* n (35) . 



