Microbial inoculants as most effective agents for degradation of chlorpyrifos in coarse textured laterite soils

Abstract Chlorpyrifos is a widely used organophosphorus insecticide and there are concerns on soil health due to excessive use in agriculture. An attempt was made to understand the effect of chlorpyrifos degradation under natural conditions and as affected by different treatments in coarse textured laterite soil of Kasaragod, Kerala, India. Results from the study revealed that chlorpyrifos content was reduced by 34.76% within 60 days of incubation period under natural conditions. Effect of physical, chemical and biological treatments on fastening the process of chlorpyrifos degradation was evaluated. Biological treatment with microbial inoculants (combination of Pseudomonas fluorescens and Trichoderma viride) showed maximum degradation (74.99 %), followed by individual application of Pseudomonas fluorescens (69.94 %) and Trichoderma viride (66.35 %) during the 60 days period of incubation. Soil enzymes such as dehydrogenase, phosphatase and urease showed significantly higher activities in treatments with Pseudomonas fluorescens and Trichoderma viride either single or combination on comparison with control. Microbial biomass carbon increased to 99.16 µg g-1 in treatment with a combination of Pseudomonas fluorescens + Trichoderma viride while control showed only 83.77 µg g-1. Degradation products of chlorpyrifos such as phosphate ions was significantly highest in biological treatment. Chlorides, sulphates and nitrate content also recorded highest values in treatment with microbial combination. Among the different agents, application of microbial combination of P. fluorescens and T. viride resulted in faster degradation of chlorpyrifos with no significant changes on chemical and biological properties of soil.