LEGUMINOUS PLANTS. 



115 



>9.-LEGUMINOUS PLANTS AS 

 SOIL RENOVATORS. 



I. As Deep Feeders. 



Leguminous plants also have 

 the advantage of being deep 

 feeders; hence, they require a 

 subsoil which they can pene- 

 trate, and alfalfa, in particular, 

 cannot be successfully o-rown if 

 the soil is underlaid with rock 

 or hard-pan. 



The roots of these plants 

 thus improve the soil in two 

 ways : 



1 . By MccJiajiical Action they 

 loosen the subsoil, making it 

 more easily penetrated by water, 

 and by subsequently formed 

 roots ; and, 



2. Che?Hical/y, by bringing 

 up from below quantities of the 

 salts of phosphorus and potas- 

 sium, as well as obtaining, 

 through the bacteria, a rich 

 supply of nitrogen from the air. 

 Large amounts of these ele- 

 ments, by the decay of these 

 roots and the stubble, are pre- 

 pared for the use of subsequent 

 crops of surface-feeding plants. 



FIG. 32. 



ALFALFA PLANT. 



lyong root-syi?tem. 



