Current Research on Geography, Earth Science and Environment Vol. 10

Biochar is widely proposed as a climate-smart soil amendment because it can immobilise contaminants, retain carbon and improve crop performance. The breadth of these claims can obscure the strong context dependence of individual outcomes and the trade-offs among remediation, carbon accounting and agronomy. This critical narrative review integrates evidence from field studies, mechanistic research, meta-analyses and life-cycle assessments, with literature searched through 4 July 2026. The evidence is strongest for three conclusions. First, biochar can reduce the bioavailability of many cationic potentially toxic elements and improve selected saline, acidic, coarse-textured or structurally degraded soils, but remediation is usually immobilisation rather than contaminant removal and may fail for anionic contaminants or poorly matched products. Second, biochar reliably increases measured soil carbon and a substantial fraction of well-produced biochar carbon can persist on centennial timescales; nevertheless, durable net carbon removal requires feedstock counterfactuals, production and transport emissions, non-carbon-dioxide greenhouse gases, native-soil-carbon responses and safeguards against double counting. Third, crop-yield responses are positive on average but highly heterogeneous, with larger benefits in acidic, low-fertility, low-organic-carbon and coarse-textured soils and much smaller mean effects in many fertile temperate systems. Water- and nitrogen-use efficiencies can improve, although the mechanisms and economic value depend on soil constraints, application rate and co-management. The synthesis supports a constraint-based deployment model: diagnose the soil problem, match biochar properties to that problem, test realistic rates under field conditions, integrate nutrient management, and monitor the claimed environmental outcome over time. Biochar can contribute meaningfully to climate-smart agriculture when treated as a specified material within a whole management system, but generic claims of simultaneous remediation, carbon sequestration and yield enhancement are not scientifically defensible.