Biochar-Based Crop-Residue Valorization as an Alternative to Open-Field Burning: A Critical Narrative Review with Emphasis on South Asia and Pakistan

Abstract

Open-field burning remains a rapid and inexpensive way to clear crop residues, but it transfers biomass carbon and nutrients from agricultural fields to the atmosphere and contributes to particulate pollution, greenhouse gas emissions, and soil degradation. This critical narrative review evaluates biochar production as one option within a wider portfolio of residue-management strategies, with global context and emphasis on South Asia and Pakistan. Sources published mainly from 2000 to June 2026 were purposively identified through Web of Science, Scopus, ScienceDirect, SpringerLink, CAB Abstracts, and Google Scholar, as well as authoritative institutional literature. Evidence was selected for relevance to residue burning, alternative management, thermochemical conversion, biochar quality, soil response, life-cycle performance, economics, adoption and policy. The literature indicates that converting suitable surplus residues to biochar can retain a comparatively persistent fraction of biomass carbon and can improve selected soil properties, particularly when biochar characteristics match soil constraints and when nutrient management is integrated. Outcomes are nevertheless heterogeneous and depend on feedstock, process temperature, residence time, soil texture and pH, application rate, ageing and co-application of nutrients. Biochar is not universally superior to incorporation, mulching, composting, animal feed, anaerobic digestion, baling or direct seeding. Its net benefit also depends on collection and transport, kiln emissions, char yield and quality, stable-carbon fraction, co-product use, competing residue demands and safeguards against contaminants and worker exposure. For Pakistan, decentralized systems may be relevant where residues are genuinely surplus, transport distances are short, and operators can control combustion and verify product quality; however, locally developed kilns require comparative assessments of emissions, safety, cost, and agronomic performance before recommendation. The strongest conclusion is therefore conditional: biochar can contribute to cleaner air, soil restoration and climate mitigation when embedded in location-specific residue planning, quality assurance and transparent life-cycle accounting.