SOIL ORGANISMS 421 



also. Greaves and Carter ^ found that a moisture content of 

 about 55 per cent, of the water-holding capacity, as determined 

 by the Hilgard method (see par. 90), was especially favorable 

 for nitrification. 



It has generally been considered that nitrification was very 

 much retarded if not actually brought to a standstill in an 

 acid soil.2 Recent data,^ however, seem to indicate that the 

 process will proceed in acid soil, although the addition of 

 lime in some form is usually beneficial. The marked stimula- 

 tion of liming to certain crops may be due partially to the in- 

 fluence of the lime on the nitrifying organisms. This rela- 

 tionship should be particularly noticeable if the crop in 

 question is unable to utilize organic or ammoniacal forms of 

 nitrogen. 



The influence of certain mineral salts is quite significant.* 

 Small amounts of salts, even those of manganese, stimulate 

 the process. Sodium nitrate, unless applied in excessive 

 amounts, promotes the nitrification of dried blood and cotton- 

 seed meal. In general, the stimulation of soil bacteria by the 

 application of fertilizer salts is coordinate with the stimula- 

 tion ordinarily observed in higher plants. Rational fertilizer 

 practice, therefore, promotes nitrification^ and no important 

 retarding influences may be expected on bacterial activity 

 unless the crop is itself directly injured. 



^Greaves, J. E., and Carter, E. G-., Influence of Moisture on the 

 Bacterial Activities of tJie Soil; Soil Sci., Vol. X, No. 5, pp. 361-387, 

 1920. 



^Hall, A. D., Fertilisers and Manure, pp. 62-64, New York, 1909. 



® Temple, J. C, Nitrification in Acid or Non-basic Soils; G-a. Agr. 

 Exp. Sta., Bui. 103, 1914. 



White, G-. W., Nitrification in delation to the Beaction of the Soil; 

 Penn. Agr. Exp. Sta., Ann. Bep. 1913-14, pp. 70-84, 1916. 



^Kelley, W. P., Nitrification m Semiarid Soils; Jonr. Agr. Res., 

 Vol. VII, No. 10, pp. 417-437, 1916. 



Brown, P. E., and Hitchcock, E. B., The Effect of Alkali Salts on 

 Nitrification; Soil Sci., Vol. IV, No. 5, pp. 207-229, 1917. 



Brown, P. E., and Minges, G-. A., The Effect of Some Manganese 

 Salts on Ammonification and Nitrification; Soil Sci., Vol. II, No. 1, 

 pp. 67-85, 1916. 



