Abstract

Fensulfothion (Dasanit) (0.0-diethyl-0-4 methyl sulphinyl phenyl monothiophos phate) when applied at 2 ppm (lower level) and 5 ppm (recommended level) concen- trations to sterilised soil inoculated with the Rhizobium sp. (Cowpea group) recorded an increase in the rhizobial numbers for 30 days during incubation and disulfoton (Disyston) (0.0-diethyl-S-2 (ethyl thio) phosphoro dithioate) showed an increase during the first 20 days. Both these chemicals. however, at 10 ppm (higher level) significan- tly depressed the population of Rhizobium in sterilised soil throughout the incubation period. In normal soil. Dasanit applications, at all the three levels, registered an in- crease in population upto 10 days and a significant reduction thereafter upto 60 days. Disyston also reduced the population of the organism at all the concentrations, the effect being more severe with the higher level. When Fensulfothion and disulfoton were added to th the growth medium in vitro and inoculated with the Rhizobium sp. 21.4% and 74.5% respectively, of the chemicals were degraded within 7 days.

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