INSTITUTE AND COLLEGE, PUSA, FOR 1912-13. 87 



in rate of one hundred per cent, or more; the concurrent 

 loss of nitrogen is not to be measured, therefore, only by the 

 increased crops taken oft' the land, but by losses in the 

 form of ammonia and of nitrate washed out during the 

 rains from fallows in we'll drained areas. 



A further point must not be overlooked; on the credit 

 side of the nitrogen account must be placed the addition 

 of this element to the soil through the intervention not 

 only of leguminous plants, but of nitrogen-fixing members 

 of the soil flora such as Azotobacter and Clostridium; the 

 physiological activity of these organisms, however, is strict- 

 ly limited by soil conditions, and especially in the case 

 of the former by the supply of carbohydrate food, so that 

 should intensive cultivation, carried out without regard 

 to this aspect of the case, lower the supply of organic 

 matter beyond the optimum point for nitrogen fixation 

 by the above-mentioned organisms, this source of nitrogen 

 would be cut off, and the discrepancy already existing 

 between the two sides of the account would be further 

 increased, probably in geometric proportion. 



During the past year Azotobacter has been found in all 

 Indian soils examined, including those of such widely differ- 

 ing character as may be found in Sind, Nagpur, and Assam ; 

 pure cultures of A . Chroococcum from such various sources 

 exhibited nitrogen-fixing power very similar to that 

 recorded from European strains, its physiological activity 

 depending upon appropriate supplies of water, air, lime 

 and especially of carbohydrate food. It is intended to 

 carry out a general survey of Indian soils to get some idea 

 of the distribution of this and similar organisms and the 

 conditions under which they may most readily carry on 

 nitrogen fixation in these soils. 



The green manuring experiment begun in collabora- 

 tion with the Imperial Agriculturist during the previous 

 year was carried on, and will continue in 1913-14. The 

 successful use of a green manure crop was found to depend 

 almost entirely upon the incidence of the rainfall succeed- 

 ing the burying of the crop, partly owing to the loss of 



