Soil Processes and Climate Solutions: From Carbon Cycling to Climate-Smart Land Management

Biochar and enhanced rock weathering (ERW) are increasingly considered complementary soil-based carbon dioxide removal (CDR) strategies because they store carbon through different pathways while potentially sharing agronomic co-benefits. Yet co-deployment cannot be assumed to be synergistic. This critical narrative review evaluates how biochar and ERW interact through soil acidity, hydrology, cation exchange, microbial respiration, secondary mineral formation, soil organic carbon (SOC) dynamics, nutrient cycling and trace-element mobility, and asks how those interactions should shape integrated climate-smart agricultural design. Literature published from 1 January 2010 to 6 July 2026 was examined, with earlier foundational studies retained where necessary. Direct combined experiments remain a small and recent evidence base, and the latest controlled and lysimeter studies continue to show strongly context-dependent responses. Their outcomes range from near-additive CDR to soil-specific stimulation of silicate dissolution, negligible interaction under alkaline or kinetically constrained conditions, and trade-offs involving native SOC mineralisation, crop responses or greenhouse-gas fluxes. Co-pyrolysis of biomass with silicate rock can create mineral-pyrogenic interfaces that modify alkalinity generation and short-term carbon stabilisation, but field validation is still limited. The central conclusion is therefore conditional rather than universal: integrated deployment can be advantageous when the amendments correct distinct site limitations, but gross carbon gains from separate components cannot be summed without accounting for interaction effects, weathering acid sources, native SOC changes, non-CO₂ greenhouse gases and upstream emissions. A robust strategy requires amendment matching to soil pH, texture, mineralogy, water regime and cropping system, combined with carbon-pool-specific monitoring, reporting and verification. The most important research need is multi-year factorial field experimentation that couples geochemical mass balance with SOC fractionation, greenhouse-gas measurement, crop performance, contaminant surveillance and life-cycle accounting.