Soil Fertility Improvement, Heavy Metal Safety and Carbon Benefits of Green Charcoal Briquettes in Maize and Cucumber Production

Abstract

Declining soil fertility and the rising cost of synthetic fertilizers are major constraints to agricultural productivity in Nigeria. Green charcoal briquettes, produced from compressed organic residues, are primarily promoted as renewable energy sources, yet their potential as safe and effective soil amendments remain underexplored. This study evaluates the chemical composition, heavy metal content and fertilizer potential of green charcoal briquettes on maize (Zea mays L.) and cucumber (Cucumis sativus L.) under screen house conditions. Laboratory analyses revealed that the briquettes contained appreciable amounts of nitrogen (1.5%), phosphorus (0.8%), potassium (1.2%) and essential micronutrients, while Pb, Cd, Cr and Hg concentrations were all below WHO/FAO permissible limits, confirming environmental safety. Application of green charcoal briquettes significantly increased maize and cucumber yields compared with the control treatment (p < 0.05), with maize biomass increasing by 25% at 4.5t ha-1 and cucumber fruit yield rising by approximately 26% at 6.0t ha-1, indicating a positive agronomic response to the amendment. Soil organic carbon improved by up to 18%, and water holding capacity increased by 15%. Estimated carbon sequestration potential ranged from 1.5 to 2.3t C ha-1, indicating notable long-term environmental benefits. These results demonstrate the dual functionality of green charcoal briquettes as both nutrient sources and carbon sinks. The study recommends their integration into sustainable farming systems, with further field trials required to validate long-term agronomic, environmental and economic benefits.