Nitrogen-Consuming Bacteria 187 



nitrification is scarcely appreciable. When such inter- 

 ference does occur, on account of excessive applications 

 of manure, the injury to crop growth cannot be ascribed 

 to denitrification. 



Bacteria that consume nitrates. — Crop growth may also 

 be affected unfavorably by certain classes of soil bacteria 

 that use up the nitrate for their own growth. This cir- 

 cumstance will be less confusing if we remember that 

 bacteria are plants competing, at times, with the 

 higher plants for their food in the soil. When conditions 

 peculiarly favor the development of these nitrate- 

 consuming bacteria, the higher plants are rapidly de- 

 prived of a part of their food, for the bacteria change 

 the nitrate into organic nitrogenous materials that do 

 not again become available until after the bacteria 

 are decayed and their bodies nitrified. We are still in 

 ignorance as to the soil and climatic conditions that 

 will favor the rapid increase of these bacteria in the 

 soil, nor do we know to what extent they are economi- 

 cally important. Even assuming that they do, at times, 

 interfere with plant growth, their activities cannot be 

 designated as denitrification. 



The denitrifying bacteria. — Finally, the injurious 

 action from excessive applications of animal manures, 

 or of other organic materials, may be really ascribed 

 to denitrification. Animal manures, particularly those 

 mixed with straw, contain vast numbers of denitri- 

 fying bacteria. When a quantity of such manure 

 is placed in a solution of nitrate, and the latter kept 

 in a warm place, the nitrate is rapidly destroyed. Within 

 two or three days, the surface of the liquid will be found 



