Effects of alpha cypermethrin and imidacloprid on soil bacteria in pot experiments of rice (Oryza sativa var. G 98–135) using soil collected from rice fields (Mahaica, Guyana)

This project endeavored to determine the effect of pesticides commonly used in rice cultivation in Guyana, on populations of heterotrophic soil bacteria as well as their effects on Azotobacter, Nitrosomonas and Nitrobacter. This experiment used Fastac, with an active ingredient of Alpha-Cypermethrin and Pronto, with an active ingredient of Imidacloprid, at recommended rates. Alpha-Cypermethrin was applied at a rate of 100 ml per acre (5 g a.i. acre−1) while Imidacloprid was applied at a rate of 15 g per acre (10.5 g a.i. acre−1). The effects of these pesticides were examined using a potted experiment in which soil was placed and then treated using a treatment regimen utilized by local rice farmers. The effect on populations of heterotrophic soil bacteria was determined by culturing on agar plates followed by enumeration of colonies grown. Azotobacter was grown using Ashby's medium while Nitrosomonas was cultured using a modified Winogradsky medium while Nitrobacter was grown using a similar, specialized medium. The results show that, at recommended concentrations, Alpha-Cypermethrin and Imidacloprid had no significant effects on the populations of heterotrophic bacteria. Similarly, the pesticides applied showed no significant effects on the populations Azotobacter and Nitrobacter. However, the results showed that the application of these pesticides resulted in increases in the population of Nitrosomonas indicating interactive behavior of soil microbes with minimum use of chemical pesticides. The research work highlights the integrated approach to cultivation of rice for sustainable crop productivity.