188 Transformation of Nitrogen 



nitrogen, was believed to be affected, the hyponitrite breaking up 

 to the oxide of nitrogen and free base. 



The presence in the soil of bacteria capable of reducing nitrates 

 to atmospheric nitrogen and oxides of nitrogen was definitely estab- 

 lished in 1882 by Gayon and Dupetit and by Deherain and Ma- 

 quenne. The same year, Lawes, Gilbert, and Warington pointed 

 out 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 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. In 1895, Wagner reported that the addition 

 of manure to liquid cultures containing nitrates greatly increased de- 

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

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

 field experiments where organic nitrogen and nitrates were added 

 simultaneously 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 may often be not only unprofitable but even harm- 

 ful. This was believed to be due to the fact that manure carries 

 microorganisms which destroy the nitrates in the soil, not only ni- 

 trates added as such, but even those formed by the nitrifying 

 bacteria. 



These and similar other investigations created the impression that, 

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

 produce an injurious action by causing the transformation of the 

 nitrate into gaseous nitrogen. It was soon found that these results 

 were greatly exaggerated. Losses of nitrogen were found possible 

 only when considerable amounts of organic matter were added 

 together with the nitrate, but this is not commonly done. Pfeiffer 

 and Lemmermann demonstrated that very little actual denitrification 

 takes place in the soil as a result of addition of manure. The lack 

 of nitrogen often observed is due to otlu>r causes rather than to 

 the loss of nitrogen. Nitrate reduction sets in when the soil is 

 saturated with water. Only in the presence of a great abundance of 

 organic manures is there any fear of loss of nitrate nitrogen in a 

 gaseous form from the soil. When soils are submerged in water, 

 the nitrates are rapidly reduced. Nitrites may be formed not at all 

 or only in too small amounts to cause plant injury. Ammonia is 

 formed in some cases. As a result of this reduction, the reaction of 



