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

Soil management sits at the intersection of three policy ambitions that are usually pursued separately: removing carbon dioxide from the atmosphere, buffering agriculture against hydroclimatic extremes, and sustaining nutrient supply for food production. The organising premise of climate-smart soil management is that these ambitions are mutually reinforcing because soil organic carbon, soil water and soil nutrients are biophysically coupled. This review evaluates how far the published evidence supports that premise, and where it does not. Literature was identified through structured searching of open scholarly indexes and citation registries, supplemented by backward and forward citation tracking and by targeted retrieval of intergovernmental technical assessments, with a final search date of 8 July 2026. Evidence was appraised for design adequacy, sampling depth and mass conventions, measurement validity, geographical representation and the correspondence between mechanistic plausibility and demonstrated field outcome. The synthesis identifies a consistent asymmetry: coupling is strong and well demonstrated in the direction running from water and nutrient availability to carbon accrual, but comparatively weak, conditional and frequently overstated in the direction running from carbon accrual to plant-available water. Reported gains in available water capacity per unit of carbon added are small in absolute terms, strongly texture-dependent, and generally smaller than the water storage differences created by texture itself. Nutrient stoichiometry imposes a material constraint on sequestration that is rarely costed in mitigation scenarios, and several practices that raise carbon stocks simultaneously alter the moisture regime in ways that increase nitrous oxide or methane fluxes, so that partial accounting can invert the sign of the climate outcome. Adaptation benefits attributable to soil carbon appear largest under moderate rather than extreme water limitation, which weakens the drought-insurance framing common in policy discourse. Priorities for future work include factorial long-term experiments that measure carbon, water and nutrient responses on the same plots, equivalent soil mass accounting to full rooting depth, and monitoring systems capable of detecting change at the scale at which management decisions are made.