LOSSES OF NITRATES FROM MANURE AND SOIL 245 



promote denitrification. 'Variations in the moisture within the 

 usual limits, however, have little influence upon the process. 



Temperature. Kruger considers that the factors which exert the 

 greatest influence upon denitrification are temperature and the 

 mechanical condition of the material which furnishes the food for 

 the organisms. These organisms function best at a temperature 

 which is high enough to greatly retard nitrification. They act very 

 energetically at a temperature of 37 C. in pure cultures, but there is 

 some evidence (von Bazarewski)" that in mixed cultures they func- 

 tion better at a lower temperature. These factors make it probable 

 that laboratory results on denitrification are high as compared with 

 field conditions even where all of the other conditions are optimum. 



The denitrifying bacteria are more resistant to light and drying 

 than are the nitrifying or nitrogen-fixing organisms. Ampola 

 found sunlight to have no effect upon two denitrifiers isolated by 

 him B. denitrificans V. and B. denitrificans VI. In pure distilled 

 water these organisms were capable of surviving for seven months. 

 When dried, B. denitrificans V died within eight weeks and B. 

 denitrificans VI was alive and active at the end of five months. 



Losses of Nitrates from Manure and Soil. The finding of the deni- 

 trifying bacteria on straw and in manure, together with the estab- 

 lishment of the fact that they can under appropriate conditions 

 decompose nitrates with the evolution of gaseous nitrogen, led 

 Wagner in 1895 to emphatically declare that the application of cow 

 or horse manures to a soil is often not only unprofitable but harmful, 

 that when applied together with nitrates they cause, by virtue of the 

 microorganisms contained in them, the destruction of the nitrates. 

 More than that, the baneful effects do not stop here, for the nitrates 

 as they are gradually formed from the organic matter of the soil are 

 also attacked by the denitrifying bacteria and their nitrogen set 

 free. In reality, then, the animal manures applied are not only 

 useless in themselves but are harmful because of their destructive 

 effects on the oxidized nitrogen derived from other sources. 



These conclusions were criticized by Warington who pointed out 

 that they were based on experiments in which the dressings of dung 

 were enormous and the same would not occur, under ordinary prac- 

 tice. The next year a serious attempt was made to solve the problem. 

 When the German Agricultural Association called for a united effort 

 on the part of the German experiment stations, offering to place the 

 necessary means at their disposal, the Experiment Stations of Augs- 

 burg, Darmstadt, Jena, Rostock, Bonn, and Gottingen responded. 

 The questions to be answered were as follows : 



1. How are the great losses of nitrogen that take place in the decay 

 of organic substances to be explained? How much of the nitrogen 

 is liberated in the elementary state and how much as ammonia? 



2. What means do we possess of checking these losses, and how 

 does the substance thus employed act? 



