Biochar in Soil Fertility Management: A Review of Agronomic Benefits, Mechanisms and Practical Applications

Abstract

Biochar, a carbon-rich solid produced through oxygen-limited pyrolysis of biomass, is increasingly considered a soil amendment for sustainable soil fertility management. Indian agriculture faces continuing pressure from soil degradation, declining soil organic carbon, nutrient depletion, crop-residue burning and climate variability, all of which constrain productivity and resource-use efficiency. This review synthesises literature and field-based evidence relevant to the use of biochar in Indian soil-crop systems. It discusses biochar production through slow, fast and flash pyrolysis using crop residues, woody biomass, and livestock or poultry manure at 300–700 °C, and relates these production conditions to key properties, including porosity, specific surface area, alkaline pH, fixed carbon content and nutrient composition. The review also examines the principal mechanisms through which biochar improves soil fertility, including modification of bulk density, water-holding capacity, aggregate stability, cation exchange capacity, soil reaction, nutrient retention and microbial activity. Evidence reviewed here indicates that biochar can reduce nutrient leaching, influence nitrogen and phosphorus dynamics, contribute to soil carbon sequestration, and mitigate selected greenhouse gas emissions, although responses depend on feedstock, pyrolysis conditions, soil type and crop requirement. Field observations from India suggest that applications within the range of 5–20 t ha⁻¹ can improve the productivity of rice, wheat, maize, legumes, oilseeds, plantation crops and vegetables, with stronger responses generally reported in acidic, sandy and degraded soils. The review further identifies practical constraints to adoption, including production cost, inconsistent product quality, limited standardisation, insufficient extension support and variable soil-crop compatibility. Integrating biochar with integrated nutrient management and decentralised residue management may support more sustainable soil fertility strategies in India.