BIOLOGY OF SOILS 



145 



obtain their nitrogen from suitable compounds in the soil. 

 If neither source of nitrogen is available the plants die; 



FIG. 19. Beans grown with (1) Nitrogen from air ; (2) Nitrogen 

 from soil ; (3) No nitrogen. 



if both are available the plants do very much better than 

 on either alone. Many farmers, though well aware of the 

 capacity of leguminous plants for obtaining nitrogen from 



S.M. L 



