SOILS AND FERTILIZERS 



soil are combined with other elements in the soil to 

 form nitric acid (HNOs). This acid combines with 



certain substances, such as 

 lime, soda, iron, and the like, 

 to form soluble nitrates. 

 They are readily available 

 to the plant. 



This process is called ni- 

 trification. The roots of leg- 

 umes furnish homes for the 

 nitrogen-fixing bacteria, 

 which abound in nearly 

 every soil. When a crop of 

 these plants is plowed under 

 and decays, great richness 

 is added to the soil. Ni- 

 trification, or fixation of free 

 nitrogen, as some call it, 

 goes on most rapidly when 

 the soil is moist and well 



FIG. 43. Tubercles on Clover Roots. j i i j 



warmed, because heat and 



moisture favor the growth of bacteria. This explains, 

 in part, why properly drained, thoroughly tilled land 

 produces better crops. 



It is thus seen how soil poor in nitrogen may, by the 

 action of bacteria on legumes, be fertilized from the 

 inexhaustible supply of nitrogen in the air. The De- 

 partment of Agriculture has made a thorough study 

 of this subject, and has succeeded in working out the 

 complete life history and habits of the bacteria in the 

 root tubercles. 



They have also discovered a cheap and thoroughly 

 effective way of distributing and applying these or- 



