Nitrification in Soils. 89 



Some of Berthelot's experiments are thought by him to 

 show that soils destitute of all visible vegetation may gain 

 large quantities of nitrogen when simply exposed to the air, 

 and he thinks he has realized gains as large as 70 to 130 Ibs. 

 of nitrogen per acre in 11 weeks. Such conclusions, how- 

 ever, require careful verification as they are at least ap- 

 parently contradicted by field practice. 



102. Nitrification. The formation of nitrates in the soil 

 involves at least four distinct phases or stages: (1) the am- 

 monia stage, (2) the nitrous acid stage, (3) the nitric 

 acid stage and (4) the nitrate forming stage. Whon 

 humus or dead organic matter is placed under the right 

 conditions of temperature, moisture and air in the pres- 

 ence of ammonia-forming germs, these organisms feed 

 upon portions of it and throw off ammonia as a waste prod- 

 uct. Ammonia is extremely soluble in water and is re- 

 tained by it in large volumes. Even dry soil has the 

 power of condensing and retaining it. In a fertile soil 

 where ammonia has been formed there are also present 

 nitrous acid germs which are able to use ammonia in their 

 life processes but throwing off nitrous acid as a waste prod- 

 uct. The niter germs or "mother of petre" utilize the 

 nitrous acid in their work and throw off as a -by-product 

 nitric acid. This nitric acid readily attacks any of the 

 bases in the soil which are held by carbonic and other weak 

 acids, displacing them and forming nitrate of lime, mag- 

 nesia, potash or soda, as the case may be. 



In the old days of "niter farming," when nitrate of 

 potash for gunpowder was obtained from the soil, great 

 pains were taken to form a soil rich in organic matter and 

 to keep it warm, well supplied with moisture and thor- 

 oughly aerated. These, too, are the points to be secured in 

 the best management of soil for farm and garden crops. 



103. Denitrification. Pitted against the processes of fix- 

 ing free nitrogen from the air, which have been described, 



