440 INVESTIGATION BY CULTURE EXPERIMENTS 



comparatively large amounts of manure used in the course of the ten seasons, we 

 must assume that denitrification is not a phenomenon of economic importance, in 

 general farming and under average field conditions. ... We have no hesita- 

 tion in emphasizing again the view expressed above that under the wide range 

 of field conditions, denitrification is not a phenomenon of economic significance 

 to the general farmer." 



With our present knowledge we should not do less than to base 

 our practice upon the known mathematical and chemical facts 

 concerning the nitrogen requirements of crops and the nitrogen 

 content of manures, legume crops, and crop residues, keeping in 

 mind, of course, that there are some soils, such as peaty lands and 

 others excessively rich in organic matter, which should be cropped 

 for years with little or no return of nitrogen. 



