EFFECT OF INSECTICIDES ON THE AVAILABILITY OF NUTRIENTS, NITROGEN-FIXATION, AND PHOSPHATE SOLUBILITY IN THE RHIZOSPHERE SOIL OF RICE

A field experiment was conducted to investigate the effects of 1,2,3,4,5,6-hexachlororocyclohexane (BHC), phorate, carbofuran, and fenvalerate, at their recommended doses, on some chemical and microbiological properties of the rhizosphere soil in relation to rice yields. In general, the insecticides had a beneficial effect on rhizosphere soil properties. Carbofuran strongly stimulated the mineralization of organic C. BHC and phorate led to the retention of less total N in the soil. BHC released more NH4+-N than the other insecticides. Phorate, however, liberated the most NO3--N. Phorate and fenvalerate. released more available P than BHC and carbofuran did. All the insecticides stimulated the proliferation of aerobic non-symbiotic N2-fixing and phosphate-solubilizing microorganisms, resulting in an overall increase in rice yield. BHC had the greatest effect on rice yields, followed by phorate.