236 NITRIFICATION 



influence in neutralizing the toxic action. Several other observers, 

 including Greig-Smith and Bottomley, claim to have found soluble 

 bacteria toxins in soil. Russell and Hutchinson, on the other hand, 

 obtained wholly negative results and concluded that soluble 

 bacterio-toxins are not normal constituents of soils, but must 

 represent unusual conditions wherever they occur. But, as pointed 

 out by Russell the possibility of the existence of toxins soluble in 

 water still remains. 



Loss of Nitrates. The loss of nitric nitrogen from a soil may be 

 either great or small, depending upon certain factors, the more 

 important of which are as follows: 



1. The rapidity of nitrification. Nitric nitrogen may be pro- 

 duced 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 than a shallow soil. 



3. The amount and distribution of rainfall. All other condi- 

 tions being equal, thirty inches of precipitation throughout the 

 year would remove more nitric nitrogen from the soil than would 

 fifteen inches similarly distributed. But if the fifteen inches came 

 within a short period, while the thirty was distributed through- 

 out 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 nitrogen 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 transform 

 nitric nitrogen into protein nitrogen, and the speed with which 

 this change occurs may at times become important; work at the 

 Utah Experiment Station indicates that this may at times reach 

 twenty or thirty pounds per acre yearly. 



The factors must always be kept in mind in an attempt to reach 

 general conclusions from any special cases, yet it is instructive to 



