74 



DRY FARMING 



same amount being turned under as came originalh^ 

 from the soil. This, however, is a great advantage over 

 other hay crops where every pound of nitrogen removed 

 represents a loss to the soil. But every ton of clover 

 tops contains forty pounds of nitrogen, so that every 



Fig. 26. — Bacteria in Belation to Soil Building. 



(a) Two piles of pure white sand, (b) The pile of sand on the left on 

 which four crops of uninoculated legumes have been grown and to 

 which nothing has been added is still white infertile sand. The pile on 

 the right on which four crops of legumes and legume bacteria have been 

 grown and to which nothing else has been added is well on the way to 

 become a fertUe soil as is shown by its dark color. 



ton of clover turned under fof the purpose of soil en- 

 richment represents a gain to the soil of forty pounds of 

 nitrogen. 



Sweet clover tops contain on the average 40 to 50 

 pounds of nitrogen per ton, so that every ton of sweet 

 clover tops turned under for soil enrichment is worth 



