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

Soil carbon has become a central instrument of climate policy, yet the operational definition of the resource being managed remains narrow. Programmes for climate-smart land management, carbon farming and soil carbon crediting are constructed almost entirely around soil organic carbon, while soil inorganic carbon, which dominates the carbon inventory of arid and semi-arid soils and constitutes a substantial share of the global soil carbon stock, is generally treated as inert background material. This review critically examines whether that separation remains defensible, and what follows for land management if it does not. Peer-reviewed literature published between 2000 and 8 July 2026 was identified through structured searching of open bibliographic and full-text scholarly sources, supplemented by backward and forward citation tracking and by targeted retrieval of intergovernmental technical documentation. Evidence was appraised for design adequacy, measurement transparency, treatment of carbonate provenance and external validity, and synthesised thematically rather than study by study. Three findings are robust across independent lines of evidence. First, the two pools are mechanistically coupled through soil solution chemistry, so that management which raises organic carbon can simultaneously dissolve carbonate, and management which accelerates carbonate precipitation may return part of the captured carbon dioxide to the atmosphere. Second, nitrogen-driven acidification and irrigation are the dominant anthropogenic controls on inorganic carbon in managed land, and both operate at rates comparable to, or exceeding, achievable organic carbon gains in calcareous systems. Third, the climate value of any inorganic carbon change depends on the provenance of the calcium involved, a criterion that most field studies do not resolve. Confidence in current quantitative projections is limited by short observation periods, shallow sampling, inconsistent carbonate correction and severe geographical concentration of evidence in China. Integrating both pools into land management therefore requires provenance-resolved accounting, deeper and mass-based monitoring, and crediting protocols that keep organic and inorganic claims separate rather than aggregating them into a single soil carbon figure.