82 REPORT OF THE AGRICULTURAL RESEARCH INSTITUTE 



Work with seedlings (wheat, oats, rice, indigo, maize. 

 dhaincha, jowar), has shown that in high concentration, 

 such as occurs in water-logged soils containing much 

 organic matter, these toxins may directly affect growing 

 plants especially seedlings, but this is an exceptional con- 

 dition, whereas it appears probable that in normal fully 

 aerated soils the toxins resulting from the ordinary 

 metabolic activity of soil bacteria are oxidized at about 

 the same rate as they are produced and no accumulation 

 takes place. A very slight interference with the oxygen 

 supply to the soil, however, will turn the scale in favour of 

 accumulation of toxins and in consequence upset the 

 natural equilibrium existing in the soil complex between 

 the toxin-sensitive nitrifying organisms on the one hand 

 and the apparently less easily affected reducing organisms 

 on the other, thus resulting in indirect injury to the crop by 

 interference with the supply of nitrogen as nitrate. In 

 soil which has been flooded during the monsoon the toxins 

 formed may persist long enough to seriously prejudice the 

 growth of seedlings if planted too soon; such soil should 

 be given as long a period of aeration as is possible before 

 planting. 



In order to ascertain the conditions under which such 

 bacterio-toxins are produced in soils a great deal of work 

 was carried out in isolating and determining the specific 

 functions of soil bacteria, but the proper development of 

 this line of enquiry would necessitate collaboration with a 

 chemical specialist. The possible bacterial origin of the 

 various organic compounds of a toxic nature which have 

 been isolated from soils by such workers as Schreiner, 

 Shorey, Skinner, Eeid and others would be one of the 

 problems involved. It was found that salts of some of the 

 heavy metals such as copper had a decided influence in 

 neutralizing the toxic action towards seedlings of extracts 

 of soils kept under anaerobic conditions; precipitation of 

 the copper as sulphide was prevented by the addition of 

 potassium cyanide, these salts being present in very small 

 quantities; (0-025 — 003 per cent. CuSOJ. It appears 



