Biomass-derived carbon materials as functional soil interfaces for sustainable agriculture

Biomass-derived carbon materials are increasingly being explored for sustainable agriculture because they can regulate soil water, nutrient availability, and biological interactions through persistent, chemically active soil interfaces. However, their role is still often discussed through fragmented perspectives, including adsorption, soil amendment, fertilizer delivery, microbial support, and carbon sequestration, without a unified framework linking precursor chemistry, processing severity, material architecture, and soil-level functionality. This review reframes biomass-derived carbon materials, including biochar, activated carbon (AC), carbon beads, granules, pellets, seed coatings, fertilizer carriers, and microbial carriers, as functional soil interfaces whose performance arises from pore accessibility, surface chemistry, mineral composition, aging behavior, and deployable form factor. Evidence from experimental studies, meta-analyses, and field-relevant observations indicates that agronomic functionality is constraint-driven rather than universally predictable, being strongly governed by soil texture, moisture dynamics, ionic strength, nutrient regime, microbial activity, application geometry, and wet–dry cycling. Mechanistically, carbon-based systems operate through coupled water redistribution, adsorption–desorption balance, nutrient buffering, pH/EC (electrical conductivity) modulation, microbial habitat formation, and localized rhizosphere interaction. These functions cannot be reliably inferred from single laboratory metrics such as maximum adsorption capacity, Brunauer–Emmett–Teller (BET) surface area, or swelling ratio. From a feasibility perspective, escalation from low-severity pyrolysis to intensive activation or chemical functionalization is not inherently justified unless it produces demonstrable gains under soil-relevant conditions. This review advances a design-oriented framework that shifts evaluation from peak material performance toward functional adequacy, process-severity awareness, deployment compatibility, and environmental robustness, positioning biomass-derived carbon materials as scalable soil-interface platforms for sustainable water and nutrient management in agriculture.