Pesticides and heterotrophic nitrogen fixation in paddy soils

The effect of three pesticides, benomyl, carbofuran and gamm-BHC at 5 parts 10⁶, rates equivalent to recommended field levels, on the heterotrophic N₂ fixation in five air-dried, cellulose-amended, submerged tropical soils was invevstigated employing ¹⁵N tracer technique under laboratory conditions. Addition of benomyl, a carbamate fungicide, to alluvial, laterite and two acid sulphate soils resulted in significant increases in N₂ fixation, while carbofuran, a methylcarbamate insecticide, exerted a stimulatory effect on N₂ fixation in alluvial, alterite and acid saline soils. Gamma-BHC, a chlorinated hydrocarbon insecticide, stimulated N₂ fixation in alluvial and acid sulphate pokkali solis, while considerable inhibition of N₂ fixation was evident inother soils. Results showed differential responses of specific groups of N₂-fixing organisms to the pesticides depending ont he soil type.