Effect of Pesticide Use on Soil Enzyme Activities in Cocoa Farmlands of Cross River State, South South Nigeria

Cocoa production in South South Nigeria relies heavily on pesticide applications to control fungal diseases, insect pests, and weeds, with potential consequences for soil biological health. This study examined the effect of pesticide application intensity on soil enzyme activities as indicators of soil biological condition in cocoa farmlands of Cross River State. Soil samples were collected from high-input, low-input, and organic cocoa farms, as well as from undisturbed forest reference sites. Activities of dehydrogenase, urease, phosphatase, and cellulase enzymes were measured using colorimetric assays. Soil physicochemical properties including organic matter, pH, and moisture content were also determined. Results showed significantly reduced enzyme activities in high-input farms compared to low-input and organic farms, with dehydrogenase activity serving as the most sensitive indicator of pesticide stress. Urease activity was positively correlated with soil organic carbon content across all farm types, suggesting that soil organic matter maintenance partially buffers enzyme suppression by pesticides. Forest reference soils showed the highest enzyme activities for all parameters measured. The study concludes that high pesticide input regimes suppress soil biological activity in Cross River cocoa farmlands and recommends adoption of integrated pest management programmes that reduce chemical inputs while maintaining production. Training for cocoa farmers in judicious pesticide application is also recommended through Cocoa Development Unit extension services. Keywords: soil enzymes, pesticides, cocoa farmland, Cross River State, soil biology.