INSTITUTE, Pl/SA, FOR 1918-19 109 



visited this district and inspected the soils in the field and 

 having carried out biological analyses in the laboratory a 

 report with recommendations for treatment was written 

 and submitted to the Director of Agriculture, Bombay. 



Nitrogen fixation. The question of the nitrogen 

 supply in Indian soils and exhaustion by the introduction 

 of intensive cultivation and heavy-yielding varieties of 

 crops was dealt with in a paper by me read at the Indian 

 Science Congress in Bombay. In this paper attention was 

 drawn to the danger of encouraging methods of exhausting 

 Indian soils without making any adequate provision for 

 keeping up the supply of the ingredients removed by in- 

 creased crop yields; the loss of nitrogen especially must be 

 guarded against when this takes place at a rate exceeding 

 that of the natural fixation by legumes and non-symbiotic 

 soil organisms. In this connection it was pointed out at 

 the Conference of Chemists and Bacteriologists at Pusa 

 in February, 1919, that special attention should be paid to 

 the study of the conditions under which nitrogen fixation 

 takes place in Indian soils, with a view to determining the 

 possibility or otherwise of artificially obtaining optimum 

 conditions for such fixation as a practical field measure. 

 The very great variations in the amount of nitrogen fixed 

 in the same soil in different years show clearly the possi- 

 bility of influencing fixation by soil management without 

 the necessity of adding impossibly expensive materials (such 

 as sugar) to the soil. In the Punjab, nitrogen to the extent 

 of 30 per cent, of that already present in a soil under single 

 crop wheat, was fixed in less than six months in one season, 

 whereas during the following one the amount was negli- 

 gible. The possible symbiotic relationship between green 

 algae and nitrogen-fixing organisms in soils formed a 

 subject for investigation at Pusa by the Supernumerary 

 Bacteriologist before the war as a continuation of his study 

 of azotobacter in India and has now been resumed on his 

 return from military service. 



Further work on fixation of nitrogen by legumes was 

 carried out and a memoir embodying the results was written 



h2 



