THE IMPACT OF PESTICIDES ON THE GROWTH OF NITROGEN FIXING BACTERIA AND PHOSPHATE SOLUBILIZING BACTERIA OF COCOA SOIL

Pesticides are used to increase crop production. Besides combating pests, pesticides affect the activity of beneficial soil microbial communities thereby affecting the nutritional quality of soils. This study aimed to determine the toxicity of pesticides derivatives on soil nitrifying bacteria. Soil samples were collected into sterile polythene bag and transported to the laboratory for analyses. Microbiological analyses of the soil samples were performed using conventional and standard microbiological techniques. The pesticides used include chlorpyrifos (an Organophosphate insecticides, acaricide and miticide) and cypermethrin (a synthetic pyrethroid insecticide). Chlorpyrifos and cypermethrin at different concentration (0.1% 0.3% ,0.7% 1%) were used as the only carbon source for selective medium used for the isolation of NFB and PSB. Results revealed the mean counts of 4.2 x 105 (CFU/g), 5.3 x 106 (CFU/g), 6.7 x 107 (CFU/g) and 7.3 x 103 CFU/g of total heterotrophic bacteria, bacterial growth on Okon red, Ashby medium and Yeast extract mannitol agar and pikokovskaya agar respectively. Toxicity results revealed that while The microbial counts were examined by serial dilution and plating methods for 3-7 days. The results demonstrated a decrease in the microbial count in all the plate supplemented with pesticides compared to the controls. No growth was recorded on plate supplemented with CYP while there’s is a high decrease in the microbial population of plate with CHL. In conclusion, this study has shown that the pesticides significantly decreased the microbial population in soil. . Therefore, this study concludes that pesticide derivatives are toxic to nitrifying bacteria at any concentration and the microbial response is dependent on concentration and hydrocarbon types. This confirms and reinforces the reports that use of pesticides in soil destabilizes soil microbial activity and ecology