114 



Partial Sterilisatio7i of Soil 



that tlie treatment has effected a small immediate production of 

 ammonia amounting to about 5 parts per million of soil, then little 

 further change takes place for a few days. This period of comparative 

 inaction is followed by one of rapid change, during which ammonia is 

 produced in considerable quantity ; lastly a slow period sets in, and the 

 further production of ammonia is now only small. By the end of 

 a month about 40 parts of nitrogen per million of soil have been con- 

 verted into ammonia. (§ 15, Table 2.) 



The difference between the " toluene evaporated " and the heated 

 soils is only one of degree. The acceleration in the rate of formation of 



20 hours 



Curve 2. Amount of ammonia produced from peptone solution after inoculation 

 with arable soil (§ 24). 



ammonia is evident at an earlier date in the toluened than in the 

 heated soil, but is not maintained for so long, and by the ninth day 

 the heated soil already contains more ammonia, a superiority which it 

 maintains throughout. 



The production of ammonia is mainly the work of micro-organisms. 

 Proof is furnished by the following considerations: 



1. The curves belong to the type associated with bacterial, rather 

 than purely chemical change (cf Curve 2). 



2. Soil which has been heated to 125° C. (at which temperature 

 all organisms are killed) behaves altogether differently : after the first 

 production of ammonia due to heating there is no further change. 



