80 REPORT OF THE AGRICULTURAL RESEARCH INSTITUTE 



{Bacillus X) the toxic action of which was found to be 

 sufficient to interfere with the growth and activity of all 

 other soil bacteria brought in contact with it or with its 

 separated toxin in culture. 



It was found that such toxins result from the decom- 

 position of organic nitrogen compounds by bacterial 

 action under semi-anaerobic conditions, and further proof 

 that the inhibition of nitrification is not due merely to 

 shortage of oxygen was afforded by the observation that, 

 with the same air supply as was sufficient for complete 

 nitrification of ammonium sulphate in soil, nitrification of 

 oilcake containing the same amount of nitrogen was com- 

 pletely inhibited, nor did it commence when complete 

 aeration was provided, until after the lapse of a consider- 

 able period (generally about two weeks although this varied 

 with different soils) when the toxins formed had had time to 

 become destroyed by oxidation, after which normal nitri- 

 fication ensued. It was found in actual practice in the 

 field that germination in a soil which had been water- 

 logged was interfered with, and that the ensuing crop was 

 consequently poor, nor was this remedied by application of 

 nitrate of soda, although the use of superphosphate was 

 successful. Laboratory experiments showed that rapid 

 reduction of nitrate takes place in water-logged soil, a large 

 proportion of nitrite being formed, and it seems probable 

 that the toxins produced during the water-logged period 

 would not only affect the germination and the growth of the 

 seedlings but that the character of the soil complex result- 

 ing from the semi-anaerobic conditions which obtained at 

 that time would be such as not only to interfere with 

 nitrification but to promote reduction for just so long as 

 this abnormal character persisted. The character of the 

 soil complex and that of the decomposition products of 

 organic matter resulting from its action must vary with 

 alterations in moisture and oxygen content of the soil itself, 

 and it is probable that the altered character may persist 

 for some time after the special conditions which gave rise 

 to it have disappeared. This point is under experimental 



