Effect of Herbicides on Fluorescent Pseudomonads and Spore Forming Bacilli

The herbicides viz., 2,4-DEE, butachlor, pretilachlor and pyrazosulfuron ethyl were evaluated at different concentrations of 1FR (Field rate), 2FR, 5FR, 10FR and 100FR for their effect on microbial population (Fluorescent pseudomonads, spore forming bacilli ) and enzyme activities (β-glucosidase, protease, alkaline phosphatase and dehydrogenase) in laboratory microcosms. The result of the experiment revealed that butachlor, among the herbicides was more inhibitory to microbial population (7.85 to 34.20% reduction over control) and soil enzyme activities (5.03 to 19.11 % reduction over control) when compared to 2,4-DEE, pretilachlor and pyrazosulfuron ethyl. The different concentrations of herbicides also exerted significant influence on the population of bacilli. The highest population of bacilli was observed in control (5.799 log CFU g^-1 soil) followed by treatments receiving 1FR (5.786 log CFU g^-1 soil) and 2FR (5.781 log CFU g^-1 soil). concentrations of herbicides. The lowest population was recorded with the 100 FR treatments (5.743 log CFU g^-1 soil). Significant differences were also observed in the population of bacilli due to the interactive influence of herbicides and concentrations. The 1FR treatments of all herbicides recorded higher population comparable to the control, while butachlor at 100FR recorded the lowest population of 5.707 log CFU g^-1 soil.