LOSS OF NITRATES 159 



direct application of Winogradsky's conclusions to the field must be 

 abandoned and with them any practices based upon them, and the 

 activities of these soil bacteria must, in the future, be studied more 

 largely under their natural environments." 



Lipman, commenting on these earlier views, believes that "the 

 exact relation of organic matter in the soil to the activities of nitrify- 

 ing bacteria is but beginning to be properly understood. Earlier 

 observation made it manifest that heavy applications of animal 

 manures, or green manure, may not only retard nitrification but 

 may actually cause the disappearance of a part or of all of the nitrate 

 in the soil. Subsequent experiments by Winogradsky and Omelianski 

 showed that in pure cultures the presence of even slight amounts 

 of soluble organic matter may depress or even suppress the develop- 

 ment of the nitrifying bacteria. It was, therefore, concluded by 

 these authors that relatively small amounts of soluble organic 

 matter may inhibit nitrification. These conclusions, based on the 

 study of liquid cultures only, were given a very broad application 

 by many writers on agricultural topics. More recent experiments 

 make it certain, however, that in the 'soil itself small amounts of 

 soluble matter, for example, dextrose, are not only harmless but 

 may really stimulate nitrification. It was shown, likewise, that 

 humus and extracts of humus may, under suitable conditions, stimu- 

 late nitrification to a very striking extent." 



REFERENCE. 



Greaves, J. E., and Carter, E. G.: Influence of Barnyard Manure and Water upon 

 the Bacterial Activities of the Soil (Journal Agricultural Research, 1916, vi, 889-926). 



