Il6 SOILS AND FERTILIZERS 



take place at as low a temperature as 3 or 4 C. 

 (37 and 39 F.); at 50 C. (122 F.) it is feeble, 

 while at 55 C. (130 F.) there is no action. 44 . In 

 northern latitudes nitrification is checked during the 

 winter, while in southern latitudes this change takes 

 place during the entire year. As a result many soils 

 in southern latitudes contain less nitrogen than soils 

 in northern latitudes where fermentation and leaching 

 of nitrates is checked by climatic conditions. Crops 

 which require their nitrogen early in the growing 

 season are frequently placed at a disadvantage be- 

 cause there is less available nitrogen in the soil at 

 that time than later. 



142. Strong Sunlight Checks Nitrification. Nitri- 

 fication cannot take place in strong sunlight ; it pre- 

 vents the action of all organisms of this class. In 

 fallow land there is no nitrification at the surface but 

 immediately below where the sunlight is excluded by 

 the surface soil, it is most active. In a cornfield it is 

 more active than in a compacted fallow field. 



143. Base-forming Elements Essential for Nitrifi- 

 cation. The presence of some base-forming element 

 to combine with the nitric acid produced is a neces- 

 sary condition for nitrification, and for this purpose 

 calcium carbonate is particularly valuable. The ab- 

 sence 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 

 strong acid or alkaline solution, consequently in such 

 soils nitrification cannot take place. 17 



