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

Among the four insecticides under study, hexachlorocyclohexane (BHC) follow ed by phorate significantly stimulated the populations of (total) bacteria, actinomycetes, fungi, aerobic non-symbiotic N-2-fixing bacteria and P-solu bilizing microorganisms in soil. Carbofuran significantly stimulated total as well as N-2-fixing bacteria. Fenvalerate had no effect on P-solubilizers . All the insecticides stimulated the proportion of Penicillium in soil. Si milarly, Pseudomonas with BHC, Sarcina with phorate, Corynebacterium, Azoto bacter 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 ins ecticides reduced the proportions of Micrococcus and Rhizopus in soil. Inse cticides also augmented the non-symbiotic N-2-fixing and P-solubilizing cap acities of the soil and the augmentation was more pronounced with BHC follo wed by phorate.