Planting Density Modulates Growth and Biomass Allocation of Cowpea (Vigna Unguiculata [L.] Walp) in Iron Industry Effluent-Contaminated Soil

Planting Density and Cowpea Growth under Effluent Contamination

Abstract

Industrialisation and improper effluent discharge practices are major contributors to soil contamination, raising concerns about crop productivity and food safety. This study assessed the influence of iron industry effluent on growth performance and biomass accumulation of Vigna unguiculata under varying planting densities. Soil samples from an effluent-contaminated site (ECS) and a non-contaminated control location (CL) were analysed, and cowpea was cultivated in both soils at five densities (1-5 plants/pot). Relevant growth, nodulation, and biomass indices were evaluated. The study revealed significantly higher levels of cadmium, lead, and organic matter in ECS compared to CL. Plants cultivated in CL exhibited higher vegetative and biomass indices and nodulation across all densities. Both effluent contamination and plant density significantly influenced most growth parameters (p≤0.05), with reduced performance at higher densities, especially in ECS. The study demonstrates that effluent-contaminated soils impair cowpea productivity and that intra-specific competition intensifies stress effects. These findings underscore the need for strict effluent management and density-specific agronomic strategies in polluted agroecosystems.