INSTITUTE, PUSA, FOR 1918-19 107 



recognition of the fact that nitrifying bacteria can perform 

 their specific function under conditions adverse to their 

 multiplication; such conditions include not only the pre- 

 sence of specific toxins but of excess of organic matter or 

 of ammonia; the immediate oxygen requirements of the 

 nitrifiers are generally satisfied in almost any soil but water- 

 logging during the monsoon not only conduces to the 

 development of toxin-producing bacteria but to the bringing 

 into solution of excessive amounts of organic matter, all of 

 which tend to depress the nitrifying flora as an indirect 

 effect of anaerobic conditions. The addition of inert mate- 

 rial of large superficial area such as broken brick or clinker 

 appears to provide a suitable nidus for the development of 

 nitrifying bacteria, not so much in the soil a.s on the surface 

 of the broken material, thus setting up conditions similar 

 to that in a sewage filter, where solutions containing con- 

 centrations of organic matter too high to allow of develop- 

 ment of nitrifying flora are nevertheless nitrified by the 

 organisms previously established on the broken surfaces. 

 It is of interest to note that in experiments dealing with 

 the addition of broken brick and potsherds to soil it is 

 necessary to make allowance for the frequently high con- 

 tent of nitrate, generally as saltpetre, found in such 

 materials in Bihar. 



A considerable amount of work was done by the First 

 Assistant on the different rates of nitrification of various 

 organic materials in soil. These included various green 

 manures and other plants, and oilcakes, and it was found 

 that the non-nitrogenous portion had an inhibiting action 

 upon the nitrification of the nitrogenous fractions. A 

 paper on this subject was read by the First Assistant at 

 the Indian Science Congress, Bombay (January, 1919). 



Further experiments on the inhibition of nitrification 

 by toxins resulting from anaerobic incubation of soils were 

 carried out ; it was found that nitrification did not begin 

 for ten weeks in Omelianski solution made up with water 

 extract of anaerobically incubated soil, whereas nitrification 

 was complete in eight weeks in a similar solution but 



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