Nitrification in Soil 



179 



Nitrification in Soil 



The production of nitrates from ammonia was known and utilized 

 long before the microbiological nature of the process was under- 

 stood. This is illustrated by the fact that during the Napoleonic 

 Wars careful instructions were given to the French farmers for 

 preparing composts of stable manure, favoring nitrate formation and 



Fig. 76. Influence of reaction on nitrification in soil, after 11 days (I), 22 days 

 (II), and 29 days (III) (from C. Olsen). 



accumulation. During our own Civil War, especially in the South, 

 "niter plantations" or "nitriaries" were common (Taber), 



The decomposition of proteins and of other nitrogenous organic 

 substances leads to the formation and often the accumulation of 

 ammonia in the soil. Under favorable conditions, this is rapidly 

 oxidized to nitrites and then to nitrates. Under certain conditions, 

 when the nitrifying bacteria are killed, as in the partial sterilization 

 of soil, or when conditions do not favor nitrification, as with exces- 

 si\e soil acidity, ammonia may accumulate in the soil. 



The oxidation of ammonia to nitrate can be accomplished by 

 three types of processes, namely, chemical, physicochemical, and, 

 most important, biological. 



At high temperatures and in the presence of catalysts, ammonia 

 may be oxidized chemically to nitrate, as in the electrolytic oxida- 

 tion of ammonia in the presence of copper oxyhydrate. Oxidation 

 may also take place, to a limited extent, in an atmosphere saturated 



