NITRIFICATION laq 



nitrification, and this is perceptible even into the second year after 

 the alfalfa has been plowed under. Hence, we can conclude 

 that alfalfa not only feeds closer upon the soluble nitrates of the 

 soil but also makes much greater drain upon the insoluble nitro- 

 gen of the soil by increasing its nitrifying powers. 



Loss of Nitrates. — ^The loss of nitrates from a soil may be 

 either great or small, depending on a number of factors, the more 

 important of which are as follows: 



(i) The rapidity of nitrification. Nitric nitrogen may be 

 produced in some soils so rapidly that even luxuriant vegetation 

 will not remove it as fast as formed, whereas in another soil it 

 may be formed so slowly that it will not suffice for even meager 

 growth. The loss in the first case may be very large, while that 

 of the second would be nearly zero. 



(2) The nature of the soil. A tight soil, other things being 

 equal, would retain the nitric nitrogen to a greater extent than 

 would a loose porous soil, and a deep soil more than a shallow soil. 



(3) The amount and distribution of rainfall. All other con- 

 ditions being equal, thirty inches of precipitation thruout the year, 

 would remove more nitric nitrogen from the soil than would fif- 

 teen inches similarly distributed. But if the fifteen inches came 

 within a short period, while the thirty was distributed thruout the 

 year, the fifteen inches of rainfall under these conditions may 

 remove more nitric nitrogen from the soil than would the thirty. 



(4) The rapidity with which the nitric nitrogen is removed 

 by the growing crop. Alfalfa, oats, and wheat are heavy feeders 

 upon nitric nitrogen and in most soils remove it as fast as formed. 

 Hence, little is left to be washed out by the drainage. Moreover, 

 crops such as these rapidly remove the water from the soil and 

 hence diminish the drainage from such soils. Moreover, crops 

 growing during the rainy season tend to conserve the nitric nitro- 

 gen where fallow soils rapidly lose nitric nitrogen during this 

 period. 



(5) The rapidity with which nitric nitrogen is transformed 

 into protein nitrogen by soil microorganisms. It is now known 

 that there are within the soil many microorganisms which trans- 



