Integrating Biochar and Basaltic Rock for Carbon Dioxide Removal via Enhanced Silicate Weathering in Semi-Arid Agroecosystems: A Critical Review

Abstract Enhanced silicate weathering (ESW) has emerged as a promising nature-based carbon dioxide removal (CDR) strategy that accelerates the natural weathering of silicate minerals to sequester atmospheric CO₂. However, its application in semi-arid agroecosystems remains comparatively underexplored, despite the importance of these environments for agricultural production and their vulnerability to climate variability, land degradation, and water limitation. In addition, the effectiveness of ESW in semi-arid agroecosystems is severely constrained by limited soil moisture, high temperatures, and degraded soil conditions. This review critically examines the integration of biochar with basalt as a synergistic approach to overcome these constraints, synthesizing evidence that has not previously been brought together within a dryland context. The review covers the geochemical mechanisms of ESW, the physicochemical properties of biochar, and potential synergistic mechanisms through which biochar may modify the soil conditions governing basalt weathering under water-limited conditions. Key co-benefits include improved soil water holding capacity, enhanced cation exchange capacity, release of plant-available base cations, increased crop productivity, and reduced nitrous oxide emissions. Environmental risks such as trace metal mobilization and life cycle considerations are evaluated. The review concludes that biochar-enhanced basalt weathering represents a potentially promising CDR approach for semi-arid agroecosystems; however, direct empirical evidence for the combined application under semi-arid field conditions remains limited.