426 NATURE AND PROPERTIES OF SOILS 



point in manuring at which reduction takes place. When 

 fifty tons or more of farm manure, in addition to a nitrate 

 fertilizer, are added to the soil, unfavorable reactions may 

 occur. Plowing under heavy crops of green-manure may 

 produce the same result. In either case the best way to over- 

 come the difficulty is to allow the organic matter partly to de- 

 compose before adding the fertilizer. The removal of the 

 easily decomposable carbohydrates needed by the reducing 

 organisms decreases or precludes their activity in this 

 direction. 



Under ordinary farm conditions conversion to free nitrogen 

 is of no significance in the soil where proper drainage and 

 good tillage are practiced. Warington ' showed that if an 

 arable soil is kept saturated with water to the exclusion of air, 

 nitrates added to the soil are decomposed, with the evolution 

 of nitrogen gas. As lack of drainage is usually most pro- 

 nounced in early spring, when the soil is likely to be depleted 

 of nitrates, it is not likely that much loss occurs in this way 

 unless a nitrate fertilizer has been added. Among the many 

 difficulties arising from poor drainage the reduction of an 

 expensive fertilizer may be no inconsiderable item. 



234. Assimilation of nitrates ajid allied compounds. 2 — 

 In addition to the nitrate-reducing organisms already men- 

 tioned, there are other bacteria and fungi that utilize nitrates, 

 nitrites, and ammonia. Like higher plants, they convert 

 the nitrogen into organic nitrogenous substances. The proc- 

 ess is therefore, one of synthesis, rather than of reduction al- 

 though reduction often occurs at the beginning of the proc- 

 ess. As such organisms operate in the dark, they must have 

 organic acids or carbohydrates as a source of energy. This 

 means of nitrate disappearance is probably of much more 



1 Warington, E., Investigations at Bothamsted Experimental Station; 

 U. S. Dept. Agr., Office of Exp. Sta., Bui. 8, p. 64, 1892. 



2 The term denitrification is often used in referring to the reduction 

 and assimilation of nitrates and allied compounds in the soil. The word 

 is so loosely used in soil literature that it has seemed best to ignore it, 

 at least for the present. 



