160 Bacteria in Relation to Country Life 



sidering the work of soil bacteria, therefore, not only 

 numbers must be considered, but, also, physiological 

 efficiency. 



Conditions affecting availability of nitrogen. — In the 

 decomposition of soil-humus and in the economy of 

 its nitrogen transformation, it has been seen that soil 

 and climatic conditions may modify the numbers, 

 physiological efficiency and species relationship of the 

 soil organisms. Certain conditions may not only favor 

 the predominant development of certain species, but 

 also a decided increase in the physiological efficiency of 

 the latter. There is reason to believe that in the breaking 

 down of the complex nitrogenous substances in the 

 humus some species may occasion slighter losses than 

 others. For this reason, the wasteful change of humus- 

 nitrogen may be due to certain species rather than to 

 others. Some of them are capable of causing intense 

 oxidation processes; that is, extremely rapid decay, 

 while others have but a feeble power in this direction. 

 Hence, the greater losses of free nitrogen under certain 

 conditions already noted. 



It seems highly important and desirable, in view of 

 the facts just stated, that our knowledge of the various 

 conditions of decay in the soil and of the manner in 

 which the bacteriological transformation of humus- 

 nitrogen is affected by soil, manuring, cultivation, and 

 crop-rotations, be increased. Such increased knowledge 

 would enable us to provide for a better conservation of 

 soil-nitrogen, and would add greatly to the economy of 

 crop-production. 



Bacteria as chemical agents. — The soil bacteria are 



