tNStlTUTE AND COLLEGE, PUSA, FOR 1910-11. 75 



its possible relation to the undoubted increase in fertility 

 resulting therefrom. It has been found that this operation 

 increases the rate of ammonification of the soil humus, pro- 

 bably by the selective action of combined desiccation and 

 abnormal temperature; similar results can be obtained by 

 heating the soil to 60° C, the soil plates shewing a survival 

 of the more active ammonifiers such as B. Mycoides and B. 

 Subtilis, v^hilst the highly aerated condition of the soil 

 inhibits the activity of surviving anaerobic spore formers. 

 The net result is an extremely rapid formation of ammonia, 

 part of which is retained by the soil and nitrified or taken 

 up directly by plants, and part is lost by diffusion; in this 

 way rapid depletion of the soil nitrogen must take place, 

 and subsequent fertility will depend upon the judicious 

 use of green manures; the economic value of the method 

 depends upon the power which it places in the hands of 

 the agriculturist of rapidly converting green manure or 

 other organic nitrogen into plant food, although this may 

 be counterbalanced to some extent by loss of nitrogen as 

 ammonia. 



Study of Pusa soil taken from depths down to nine feet 

 shows large numbers of bacteria even at this low level; 

 nitrification has been found actively proceeding in the third 

 foot from the surface, the greatest amount of this taking 

 place in the second six inches. Owing to the open texture 

 of this soil it is improbable that denitrification occurs to any 

 appreciable extent, but the rapid rate of ammonification 

 and the vigorous growth of soil bacteria no doubt interfere 

 with the production of nitrates. 



A method of quantitative estimation of the changes in 

 soil due to bacterial action, by periodical analysis of the 

 soil gases, has given much information as to the conditions 

 favourable for nitrification in soils; it is hoped that this 

 method will be invaluable in the future for dealing with 

 such problems as arise out of soil irrigation and drainage, 

 and the use of green manures. 



In connection with the experiments upon soil steriliza- 

 tion as a laboratory method, investigations have been car- 



