INFLUENCE OF REACTION UPON NITRATE FORMATION 141 



position and is consequently converted to inorganic compounds 

 very slowly. In certain soils, after the ammonia is changed to 

 nitrite it may persist in that form for a considerable period of 

 time and only gradually be changed further to nitrate. 



Influence of Soil Reaction upon Nitrate Formation. — 

 The more acid a soil is, the less nitrate is formed; when the reac- 

 tion is too acid, nitrate formation may come to a standstill (Fig. 60). 



8.0 1 



NaHCOj 

 Reaclion-pH 



10.0 /ll.O 

 Too ^82003 



Fig. 60. — Influence of reaction upon nitrate formation 

 (after Meyerhof). 



In slightly alkaline soils, conditions appear to be particularly 

 favorable for nitrification. The addition of lime to acid soils 

 generally favors the formation of nitrate. 



In certain arid regions of the West, particularly in Colorado and 

 Utah, there are limited areas of basic soils so rich in nitrate salts as 

 to prevent plant growth. Although nitrification in these soils is 

 very active, the large quantity of nitrates probably has not been 

 formed in these so-called " nitre spots," but has been produced 

 principally in the soils of the vicinity and concentrated in the spots 

 by the various movements of the soil water in these areas of 

 deficient rainfall. 



