124 



BACTERIA AND SOIL FERTILITY 





Soil 





Irrigated 



Dry-farm 



First 1 2 inches 

 Second 12 inches 

 Third 12 inches 



19-39 



2.70 



1.98 



2.41 



it nitrates; hence, they are dependent upon the ammonifying or- 

 ganisms for their supply of crude material on which to work, and 

 this requires a supply of readily decomposable organic material. 

 Hence, the addition of manure and plant residues to a soil in- 

 creases its nitrifying powers. This is seen from the following 

 results obtained at the Greenville (Logan) Experimental Farm: 





Percent Nitrates Formed Untreated Soil 100 





Fallow 



Cropped 



No manure 

 5 tons manure 

 15 tons manure 



100 

 1,211 



2,240 



100 



453 

 2,079 



Even when twenty-five tons of manure were applied to this 

 soil excellent team work was done by the various classes of bac- 

 teria, so that the nitrogen eventually appeared as nitrates without 

 any appreciable loss of nitrogen. 



Oxygen. — In addition to ammonia on which to work there 

 must be oxygen with which the ammonia can be transformed into 

 nitrites, and eventually into nitrates. Hence, nitrification is best, 

 other things being equal, in a well-aerated soil. This is illustrated 

 by the work of Schlosing who exposed soil for four months to an 

 atmosphere containing different percentages of oxygen. That 

 which contained 1.5 per cent of oxygen yielded 45.7 mg. of nitric 

 nitrogen, that containing 6.0 per cent yielded 95.7, that contain- 

 ing II per cent yielded 132,5 mg., whereas that containing 16.0 

 per cent of oxygen yielded 246.6 mg. of nitric nitrogen. 



