The Effects of Pesticide Application on Soil Microbiota and Weed Dynamics in Cowpea Cropping Systems

Soil is a critical habitat for diverse microorganisms and plants, pivotal in nutrient cycling, organic matter decomposition, and overall ecosystem productivity. However, agricultural practices often involve the use of pesticides to manage pests and increase crop yield, which can significantly impact soil biodiversity and health. Pesticides such as dimethoate (an organophosphate insecticide) and lambda-cyhalothrin (a synthetic pyrethroid) are commonly used in farming to control insects and pests that threaten crops like cowpea (Vigna unguiculata). This study investigates the impact of Dimethoate (A), Lambda-Cyhalothrin (B), and their combination (A+B) on soil microbial and weed populations. Soil samples were sourced from BIODEC Katsina and cowpea seeds were obtained from IITA, Kano office, Nigeria. Microbial enumeration and identification were performed using standard pour plating and biochemical techniques. Results showed pesticide concentrations influenced microbial populations, with A+B at 40 mL/L yielding the highest bacterial (39.75 CFU/g) and fungal (34 CFU/g) counts. Dimethoate alone at 50 mL/L resulted in the lowest bacterial (7.25 CFU/g) and fungal (8 CFU/g) counts. Synergistic effects were observed with A+B, promoting microbial proliferation and weed growth at moderate concentrations. Correlation analysis revealed a strong negative relationship between Dimethoate and microbial populations (r = -0.921, p < 0.001) and a positive correlation for Lambda-Cyhalothrin (r = 0.731, p < 0.01). The findings highlight the potential of pesticide combinations to alter soil microbial dynamics and weed populations. Judicious and selective use of pesticides to target pests while preserving beneficial soil organisms is recommended.