Insecticidal effects on soil microorganisms and their biochemical processes related to soil fertility

Among the four insecticides under study, hexachlorocyclohexane (BHC) followed by phorate significantly stimulated the populations of (total) bacteria, actinomycetes, fungi, aerobic non-symbiotic N2-fixing bacteria and P-solubilizing microorganisms in soil. Carbofuran significantly stimulated total as well as N2-fixing bacteria. Fenvalerate had no effect on P-solubilizers. All the insecticides stimulated the proportion of Penicillium in soil. Similarly, Pseudomonas with BHC, Sarcina with phorate, Corynebacterium, Azotobacter and Streptomyces with fenvalerate were also stimulated. On the other hand, Erysipelothrix with BHC, Staphylococcus with phorate, Staphylococcus, Nocardia and Fusarium with fenvalerate were inhibited. Almost all the insecticides reduced the proportions of Micrococcus and Rhizopus in soil. Insecticides also augmented the non-symbiotic N2-fixing and P-solubilizing capacities of the soil and the augmentation was more pronounced with BHC followed by phorate.