Effects of Chemical Fertilizers and Herbicides on Accumulation of Some Heavy Metals in Wetlands Under Different Land Use Types in Odeda, Southwest Nigeria

Abstract

This study investigated the effects of chemical fertilizers and herbicides application on the wetland soils at the Federal University of Agriculture, Abeokuta and Odeda Farm Settlement, Eweje. The land use types studied were maize, plantain, rice, vegetable, and fallow land. Data on land history, land use and management practices, and concentrations of heavy metal were collected through field surveys, interviews, and nutrient analysis. Concentration of copper, cadmium, iron, manganese, lead, and zinc were assessed. The surface water quality was assessed using WHO maximum permissible limits. Heavy metal in the soil samples ranged between 0.06 mg/kg and 262.35 mg/kg across the land use types. The concentration of metals like Fe, Mn, Cd, and Pb in the surface water of agrochemical applied fields were above the WHO permissible levels for agricultural and domestic purposes. The soil cultivated years, the types and quantity of applied fertilizers, timing of application, and land use patterns were the main reasons for differences in the heavy metal content of the soils. The study concluded that application of agrochemicals polluted the wetlands, thereby making the water toxic. Soil testing programme should be conducted on agricultural land before any use, and proper agronomic practices of production should be adopted to minimize uncontrolled agrochemical usage.