Significance of Denitrification 185 



Value of the modern discoveries. — No practical signifi- 

 cance was attached to these discoveries until 1895, 

 when the statement of Wagner, in Germany, that the 

 use of barnyard manure leads frequently to serious 

 losses' of nitrogen from the soil recalled the attention 

 of chemists ,and bacteriologists to the subject. It was 

 held by Wagner that the application of manure and 

 nitrate is a very wasteful practice, since the denitri- 

 fying bacteria, present in large numbers in the manure, 

 cause the destruction of the nitrate in the fertilizer. 

 Furthermore, they reduce the nitrates formed from the 

 soil-humus by the nitrifying bacteria. Wagner's state- 

 ment naturally aroused much comment and stimu- 

 lated extensive investigations in Germany, England, 

 France, the United States, and elsewhere. 



Modern conclusions concerning denitrification. — The 

 conclusions as they were reached after five or six years 

 of study may be summarized briefly as follows : It 

 was demonstrated that under certain conditions the 

 applications of large quantities of manure may really 

 decrease the yields, in some cases to a very serious 

 extent. The injury thus occasioned may be due to the 

 direct action of the organic materials in the manure on 

 the plants, or it may be bacteriological in character. As 

 to the former source of injury, it should be remembered 

 that excessive amounts of soluble organic materials 

 like those in liquid manure may, of themselves, prove 

 injurious to the plants. In ordinary field practice the 

 amounts of manure applied are never large enough to 

 cause such injury. In market-gardening, or in green- 

 house work, in both of which applications of as much as 



