Soil inorganic carbon sequestration through alkalinity regeneration using biologically induced weathering of rock powder and biochar

Soil inorganic carbon (SIC) accounts for about half of the C reserves worldwide and is considered more stable than soil organic carbon (SOC). However, soil acidification, driven mainly by nitrogen (N) fertilization can accelerate SIC losses, possibly leading to complete loss under continuous and intensive N fertilization. Carbonate-free soils are less fertile, productive, and more prone to erosion. Therefore, minimizing carbonate losses is essential for soil health and climate change mitigation. Rock/mineral residues or powder have been suggested as a cheaper source of amendments to increase soil alkalinity. However, slow mineral dissolution limits its efficient utilization. Soil microorganisms play a vital role in the weathering of rocks and their inoculation with mineral residues can enhance dissolution rates. Biochar is an alternative material for soil amendments, in particular, bone biochar (BBC) contains higher Ca and Mg that can induce even higher alkalinity. This review covers i) the contribution and mechanism of rock residues in alkalinity generation, ii) the role of biochar or BBC to soil alkalinity, and iii) the role of microbial inoculation for accelerating alkalinity generation through enhanced mineral dissolution. We conclude that using rock residues/BBC combined with microbial agents could mitigate soil acidification and SIC losses and also improve agricultural circularity. [Figure not available: see fulltext.]