No. 4.] MTKOGrEN AND FEliTlLlTY. 175 



Nitrification. 



Most soils have the nitrifying bacteria already present, so 

 that a stimulation of their action is needed, rather than the 

 addition of more bacteria of the same kind. If it is neces- 

 sary to supply more of the nitrifying bacteria, this can be 

 readily done Ijy the use of farm manure, which contains 

 them in abundance. The question, therefore, of the great- 

 est importance is how the nitrifying bacteria in a soil can be 

 stimulated so as to act upon the store of organic nitrogen 

 which is contained in the humus. For the favorable growth 

 of these bacteria the soil should be neither too dry nor 

 should it be saturated with water. Nitrification begins to 

 take place at a temperature of about 37° F., and becomes 

 more vigorous as the temperature rises. It therefore ceases 

 with us in the winter and is most vigorous in midsummer. 

 Nitrification will not proceed in an acid soil ; hence it fre- 

 quently happens that the addition of even a small amount 

 of lime has a wonderful eftect, — far more than can be at- 

 tributed to the fertilizing value of the lime itself. For the 

 same reason the addition of a small amount of manure to a 

 soil frequently produces results far beyond the fertilizing- 

 value of the manure. In the first place, the manure is sure 

 to be alkaline, which may be sufficient to neutralize the 

 acidity of the soil ; and it also adds large numbers of the 

 nitrifying bacteria to the soils. 



Another most important thing that has been found is, that 

 the nitrifying bacteria require large supplies of oxygen, and 

 nitrification is therefore stimulated by anything which tends 

 to add more air to the soil. This points to and partly ex- 

 plains the value of thorough cultivation. Merely the stir- 

 ring up of a soil will materially add to its available nitrogen, 

 even without the addition of any plant food. Experience 

 has shown that the more thorough the cultivation the greater 

 is the nitrification and the larger the crops. This also ex- 

 plains why the process of fallowing, which was formerly 

 practised, is not a good one. Fallow land is worse than 

 wasted, for the nitrification not only is relatively reduced, 

 but, there being no plants to take care of what little is 



