Xitrification. 189 



grains. This is due in no small measure to the larger 

 amount of nitrogen rendered available because of the 

 favorable conditions for the nitrate-forming bacteria in 

 scil which is frequently stirred. 



It is essential that the soil shall contain some sub- 

 stance, as lime, to combine with the nitric acid formed, 

 otherwise the soil soon becomes acid and nitrification is 

 no longer possible. In a marshy soil the process may go 

 on slowly or not at all. If an application of lime is made 

 and the acidity neutralized, nitrification begins. In 

 such a soil the process is also favored by drainage and 

 cultivation since the aerobic forms of life gradually de- 

 stroy the acid products that have been formed by the an- 

 aerobic bacteria. 



The change of ammonia to nitrates can not go on in 

 the presence of large amounts of organic matter, as for 

 example in a manure heap. The nitrifying bacteria are 

 unable to grow in a very dry soil. The process of nitri- 

 fication reaches its maxium in the soil during the sum- 

 mer, especially during June and July, when the need of 

 the growing crop for nitrates is greatest. It goes on, 

 however, during the fall and to some extent as long as 

 the ground is not frozen. The reason for the greater 

 rapidity of the formation of nitrates during the early 

 summer is found in the favorable temperature condi- 

 tions, together with the large amount of ammonia that 

 is formed from the decomposition of the previous year's 

 crop. 



The sodium nitrate that is used for fertilizer and in the 

 chemical industries is obtained in Chile where there are 

 large deposits. These are supposed to have been formed 

 by the decomposition of sea weed under such conditions 

 that the resulting nitrate was not leached away. Im- 



