REDUCTION PROCESSES IN THE SOIL 553 



of nitrogen. Lawes, Gilbert and Warington pointed out the same 

 year that considerable quantities of nitrogen may be given off when a 

 soil receives heavy applications of manure and is saturated with water or 

 is improperly aerated. Breal 44 announced in 1892 that many substances 

 of organic origin, especially straw, can serve as sources of energy which 

 would enable the bacteria to liberate atmospheric nitrogen from nitrates. 

 This is seen from table 54, where 2 grams of straw and sodium nitrate 

 were added to 400 cc. of water. Breal emphasized the conclusion that 

 denitrification is not of any importance in normal soils, but may become 

 so in humus-rich forest soils. In 1895 Wagner 45 reported that the addi- 

 tion of manure to liquid cultures containing nitrates greatly increased 

 denitrification; this observation led him to the conclusion that the same 

 process takes place in the soil. He found confirmation in this in field 

 experiments where organic nitrogen and nitrates were added simulta- 



TABLE 54 

 Influence of straw wpon denitrification in solution 



Nitrogen content of straw 



Nitrogen content of nitrate added 

 Total nitrogen added 



Nitrogen found at end of experiment 

 Nitrogen lost into the atmosphere . . . 



MILLIGRAMS 



9.7 

 26.0 

 35.7 



27.1 

 8.6 



neously before the crop was planted. Wagner declared, on the basis of 

 these experiments, that denitrification may take place extensively in 

 cultivated soils; the application of manure (cow or horse) to the soil 

 was believed to be often not only unprofitable but even harmful; this 

 was believed to be due to the fact that manure carries microorganisms 

 which destroy the nitrates in the soil, not only added as such, but even 

 those formed by the nitrifying bacteria. 



These, as well as similar other investigations, created the impression 

 that when nitrates are added to the soil denitrification sets in and may 

 cause an injurious action by causing the transformation of the nitrate 

 into gaseous nitrogen. It was soon found that these results were greatly 



"Breal. Compt. Rend. Acad. Sci., 114:681-683. 1892; Ann. Agron., 18: 

 181; 22: 32; Deherain, 1902 (p. 793). 



45 Wagner, P. Die geringe Ausnutzung des Stallmiststickstoffs und ihre 

 Ursachen. Deut. landw. Presse, 22: 98. 1895; see also 1897 (p. 185). 



