AND COLLEGE, PUSA, FOR 1914-15. 85 



The effect of various trees upon nitrification due to the 

 fall of their leaves upon the ground was studied and con- 

 siderable differences were observed. 



The optimum amount of organic matter as oilcake 

 containing 5 per cent, nitrogen for nitrification in Pusa 

 soil was found to be about 1 per cent, of soil weight. At 

 a concentration of 2 per cent, ammonia formation was so 

 rapid as to result not only in inhibition of nitrification but 

 in loss of nitrogen as ammonia gas ; the free ammonia also 

 brought organic matter into solution and made it necessary 

 to abandon the use of the tintometer for estimation of 

 nitrates and to use the aluminium reduction method, which 

 was found more convenient and reliable for this particular 

 purpose than the zinc-copper couple. Indications were 

 obtained that the prejudicial effect of organic matter upon 

 nitrification is in many cases due to the rapid multiplica- 

 tion of toxin-producing bacteria consequent on its presence. 



The effect of temperature on nitrification in Pusa soil 

 was tested, the optimum being found to be near 35° C. ; no 

 nitrate was formed at 40° C, nor did nitrification take 

 place in soil which had been kept at 40° C, when its 

 temperature was afterwards reduced to 30° C. ; further 

 work on this point is being carried out to determine the 

 cause of this apparent lowering of the thermal death point. 



A series of experiments was carried out to determine 

 if possible for what reasons on adding as solids such 

 bacterial food stuffs as oilcake or sugars, to a live soil, the 

 evolution of carbon dioxide resulting from bacterial action 

 should rise in rate for a few days but fall again rapidly 

 to a minimum long before exhaustion of the food supplied 

 could be called upon to account for such diminution in 

 activity. Reasons were found for thinking that this result, 

 invariably obtained when solid nutrients were added to 

 soil, was due in part to auto-intoxication by the soil 

 bacteria, and in part to the purely physical facts of the 

 case, depending upon the ratio between the superficies and 

 the cubic contents of the particles of organic matter in- 

 volved, and the possible protection against solution by 



