214 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



If a soil is to be used, 1 it is mixed with a small amount of am- 

 monium sulphate, cottonseed meal or some other nitrogenous 

 material, and water. Fresh moist soil may be used, or air-dry 

 soil, which is inoculated with other soil to furnish the bacteria. 

 It is hardly practical to sterilize the soil by heat, as this changes 

 its chemical character decidedly. After incubation for a period 

 of 30 to 50 days, nitrates are estimated in the soil. Nitrification 

 in the soil is different from nitrification in solution. Cottonseed 

 meal added to a soil will nitrify, while if added to solution, it will 

 putrify. 2 



Nitrification, ammonification, and similar soil activities, may be 

 studied with respect to the soil, or with respect to the organisms. 3 

 Nitrifying capacity 4 may be defined as the capacity of a soil to 

 serve as a medium for the growth of nitrifying organisms, com- 

 pared with a standard soil, both soils being provided with equal 

 members of bacteria of the same activity, with equal amount of 

 nitrogenous compounds, and kept under similar conditions. 

 Nitrifying power may be defined as the ability of a soil to set up 

 nitrification in a soil or culture medium inoculated with it, and is 

 a measure of the number and activity of the organisms in the soil. 

 Similar terms may be applied to other bacterial activities. 



Conditions Favorable for Nitrification. The conditions favor- 

 able for the development of the nitrifying organisms, as 

 established by experiments, are as follows : 



(1) Suitable Food. Potash, phosphoric acid, lime, sulphates, 

 and carbon dioxide appear to be essential. 



(2) Presence of Base. The nitric acid must be neutralized, as 

 the organisms will not thrive in an acid medium. Calcium car- 

 bonate or sodium bicarbonate are effective. Too much base is 

 injurious. 



(3) Suitable Temperature and Moisture. Nitrification is 

 most active at 36. It almost ceases at low temperatures. 



1 Am. Chem. Jour., 1903, p. 225 



2 Report North Carolina Exp. Sta. 1902-3, p. 27. 



3 Stevens and Withers, Proc. Ass. Off. Agr. Chem., 1909, p. 34. 



4 Texas Bulletin, 106. 



