EFFICACY OF BIOCHAR AND COMPOST AMENDMENTS ON LEAD AND CADMIUM IMMOBILIZATION AND GROWTH OF CORCHORUS OLITORIUS IN CONTAMINATED SOILS

Abstract

Heavy metal contamination of agricultural soils poses significant risks to ecosystem health and food safety, particularly in tropical regions with intensive industrial and farming activities. This study evaluated the efficacy of organic amendments, biochar (poultry litter-PLB; maize cob-MCB), and compost (CM), applied singly and in combination for simultaneous remediation of lead (Pb) and cadmium (Cd) contamination and performance of Corchorus olitorius as a test crop. The experiment was conducted for two years on an iron-pot industry dumpsite and a Fadama soil using compost and biochar alone and in combination (ratio 3.2), at the rate of 10.7 g/kg soil. The study assessed soil pH, heavy metal concentrations, plant growth, biomass yield, and metal uptake, determined 6 weeks after planting, following standard procedures. Data were analyzed using descriptive statistics, polynomial regression, and ANOVA. Results demonstrated that MCB alone achieved the highest metal immobilization, reducing Pb and Cd bioavailability by 79.3% and 65.2%, respectively, through pH-dependent precipitation and surface complexation mechanisms. Combined PLB+CM treatment optimized plant productivity, increasing fresh biomass 4-fold compared to controls while maintaining effective metal immobilization (56.8–59.8% Pb reduction). Notably, amendment effects were soil-context dependent: dumpsite soils exhibited greater remediation potential, while fadama soils showed superior growth responses. Bioaccumulation factors confirmed C. olitorius as an effective excluder for Pb (BAF: 0.01 – 0.02) but indicated higher Cd uptake (BAF: 0.06 - 0.38), mitigated by amendment applications. The study establishes that: (1) biochar-compost synergies balance remediation and agronomic goals, (2) amendment selection should consider soil type and contamination level, and (3) locally-sourced organic amendments offer sustainable solutions for tropical metal-polluted agroecosystems. These findings provide actionable insights for policymakers and farmers, advancing phytomanagement strategies that reconcile environmental safety with food production in developing economies.