INSTITUTE AND COLLEGE, PUSA, FOR 1911-12. 11 



fully rid of a plague of bugs by the application of hydro- 

 cyanic acid. 



9. Bacteriology. — The principal work of this section 

 during the past year has been the study of the factors 

 which determine the biological activity of Indian soils, and 

 the devising of methods by which this activity may be ascer- 

 tained and measured. The usual plan of estimating bacteria 

 by '' plating " has been abandoned in favour of the measure- 

 ment of their resulting physiological activities. Thus, for 

 example, it has been ascertained that the biological activity 

 of a soil is in direct proportion to the rate of formation of 

 carbon dioxide, and that conditions unfavourable to the 

 former will also adversely influence the latter. It is possi- 

 ble in this way to determine the optimum conditions of 

 moisture content, the effect of the addition of various 

 manures, organic and mineral, and the influence which 

 tillage will have upon any particular soil. The biolysis of 

 green manures, root residues, and organic manures, in so 

 far as they form the supply of available nitrogen, has been 

 undertaken. 



It has been found that important differences exist in 

 the biological changes that take place in Indian and Euro- 

 pean soils. These differences appear to be due mainly to 

 the relatively higher temj^eratures and consequent greater 

 bacterial activity of Indian soils. At temperatures between 

 15° C. and 18° C. the formation of ammonia is in pro- 

 portion to the nitrification which follows it, but when 

 temperatures rise from 25° C. to 30° C. ammonification 

 may proceed with such rapidity that nitrification is inter- 

 fered with, and even inhibited altogether, by an excess of 

 ammonia. If, therefore, large quantities of organic matter 

 are applied to a soil, much nitrogen may be lost in the form 

 of ammonia — which shows the necessity that exists for 

 selecting the most suitable time of year for applying organic 

 manures. It has also been ascertained that where intense 

 bacterial action is taking place in a soil, nitrates present 

 will be reduced, without the occurrence of anserobic condi- 

 tions, lending support to the belief that the nitrate is 



