182 Bacteria in Relation to Country Life 



by bacteriological activities. Some of these substances 

 are more resistant to the attacks of the organisms and 

 are converted into ammonia and nitrate slowly, while 

 others are changed rapidly. It may also be that in the 

 process of ammonification and nitrification, gaseous 

 nitrogen is set free, and that these losses are different 

 with different substances. The available substances, 

 that is, those that nitrify rapidly, are more like nitrate 

 in their action than are the slowly available substances. 

 Influence of the crop on availability. — It has been 

 demonstrated in the case of some plants that the crop 

 may favor or retard nitrification, not only by with- 

 drawing greater or slighter amounts of moisture from 

 the soil, but, also, by modifying, however slightly, the 

 chemical nature of the latter. It was thus shown, in the 

 case of wild mustard, that the nitrifying action of the 

 soil had been diminished, the effect showing also in the 

 following season. An interesting field of inquiry is thus 

 opened to us. Studies in this direction will undoubtedly 

 prove of great value, and will help us to understand, 

 perhaps, the beneficial effect of crop-rotations in so far 

 as they concern the soil bacteria. 



