NITRIFICATION 123 



140. Base-forming Elements Essential for Nitrifi- 

 cation. — The presence of some base-forming element to 

 combine with the nitric acid produced is a necessary 

 condition for nitrification, and for this purpose calcium 

 carbonate is particularly valuable. The absence of 

 basic materials is one of the frequent causes of non- 

 nitrification. In acid soils, the process is checked for 

 the want of proper basic material. The organisms 

 which carry on the work cannot exist in a strong acid 

 or alkaline solution, consequently in strong acid or 

 alkaline soils the ordinary process cannot take place. 16 



141. Nitrous Acid Organisms. — There are at least 

 two nitrifying organisms in the soil : one produces 

 nitrates and the other nitrites or nitrons acid. It is 

 believed that the process takes place in two stages, the 

 first being performed by the nitrous organism, and the 

 process completed by the nitric organism. Warington 

 says that "both organisms are present in the soil in 

 enormous numbers, — and the action of the two organ- 

 isms proceeds together, as the conditions are favorable 

 to both." 



142. Ammonia-producing Organisms. — There are 

 also present in the soil organisms which have the 

 power of producing ammonia from proteid bodies. 

 The ammonium compounds produced are acted upon 

 bv the nitrifying organisms and readilv undergo 

 nitrification. 45 



143. Denitrification is just the reverse of the nitri- 



