THE MICRO-ORGANIC POPULATION- OF THE SOIL 263 



organisms. A careful distinction must be made between the 

 nitrifying power ascertained from culture media and the rate 

 at which nitrates accumulate in the soil. The experiments 

 in culture media measure the rate of nitrification under the 

 circumstances of the experiment : the accumulation of nitrate 

 in the soil, on the other hand, measures the rate of ammonia 

 production (p. 1 88). 



The "ammonifying power" or " putrefactive power" is 

 determined by inoculating soil into a I per cent, peptone 

 solution, and determining the ammonia formed after incubation 

 at 20. Remy found that certain soils known to give good 

 crop returns for organic manures also possessed high putre- 

 factive power. He incubated for four days, but Russell and 

 Hutchinson (241^) obtained better results by taking definite 

 intervals and plotting curves showing the respective rates of 

 ammonia production by the different soils. Lohnis has used 

 this method a good deal (i8i) as also has J. G. Lipman, who, 

 however, modifies it considerably, and among other things 

 uses sterilised soil as the medium and substitutes dried blood 

 or cotton-seed meal l for peptone (176). Percy Brown (60) 

 used a similar modification in his studies of Iowa soils, and 

 found that the "ammonifying power" ran along with the 

 "nitrifying power" and, in four out of the six plots, with the 

 crop-producing power also (Table LXVIIL). 



Other workers have observed a general similarity between 

 ammonifying power and productiveness which, however, 

 frequently breaks down in individual cases. Further, the 

 differences between good and poor soils are not particularly 

 marked and would often be considered to lie within the error 

 of the experiment. The relationship with productiveness is 

 therefore less definite than in the case of nitrification. 2 



1 Sackett (Colorado Bull., 184, 1912) has shown that these cannot be used 

 indiscriminately ; in some soils dried blood is ammonified more rapidly than 

 cotton-seed meal while in others the reverse holds. 



2 For evidence to this effect see P. S. Burgess (63), Gainey, Soil Sci., 

 !9i7 3. 399; Kelley, Science, 43, 30-33, and Hawaii Bull., 37, 1915, p. 52 ; 

 Stevens and Withers (271) ; J. G. Temple, Ga. Bull., 126, 1919. 



