TRANSFORMATIONS OF CARBON AND NITROGEN. IO/ 



tivity of the nitrobacteria demands an alkaline medium and the 

 presence of even a slight amount of acid checks their action. 

 Hence it frequently happens that the addition of a little lime 

 to soil produces a wonderful effect, far more than can be ac- 

 counted for by the fertilizing value of the lime itself. The lime 

 neutralizes the acids present and furnishes the proper condi- 

 tions for the growth of the nitrobacteria. Here too we find 

 doubtless, the explanation of the great effect sometimes seen 

 to follow the addition of a little manure to a poor soil. The 

 manure is sure to be alkaline in reaction, and if it be added to 

 a soil which is acid, it may at once stimulate the activity of the 

 nitrifying bacteria by neutralizing the acids. The nitrifying 

 bacteria will begin then to convert the soil nitrogen compounds 

 into nitrates and a greatly increased yield of crops may follow. 

 This is doubtless another factor in explaining the oases of green 

 which surround the droppings of cows in old pasture lands. 



Perhaps the most important result of these studies, from the 

 practical side, has been the conclusion that nitrification de- 

 mands a good supply of oxygen and is, therefore, stimulated by 

 anything which increases the thoroughness of the mixture of 

 air with the soil. This points to the great advantage to the 

 soil of tlwrougJi cultivation, and teaches that the more thor- 

 oughly the soil is stirred the better the results. Such cultiva- 

 tion more uniformly distributes the moisture and this stimu- 

 lates the bacteria growth. The simple stirring up of the soil 

 will thus actually increase its fertility by stimulating the con- 

 version of its nitrogen compounds into nitrates through the 

 agency of nitrification. The more thorough the cultivation the 

 better, and experiments indicate that a complete pulverization 

 of the soil has a very decided value in increasing its fertility. 

 These facts have entirely done away with the idea that the land 

 should be allowed to lie fallow once in a few years. Fallow 

 land is worse than wasted. The nitrification becomes very 

 slight, and what nitrates there are present are rapidly drained 



