COUSINE v1.0.0-site: model code for "Optimizing carbon dioxide removal in agricultural soils: A new mechanistic model of enhanced rock weathering"

Abstract

Enhanced rock weathering (ERW) has the potential for gigatonne-scale CO2 removal (CDR) annually by introducing finely crushed alkaline minerals into global agricultural soils. However, questions remain about how soil inorganic carbon forms across complex conditions in cropland soils. Here we present COUSINE (COUpled Soil Inorganic-organic carbon model for eNhanced wEathering), a new model that mechanistically quantifies CDR via ERW across diverse environmental conditions. COUSINE couples a seven-pool soil organic carbon module with a soil inorganic carbon module tracking 20 chemical species, driven by soil CO2 dynamics, parent material weathering, cation exchange, strong and weak acid weathering, and leaching. Mass and charge conservation are maintained across all reactions, and all processes are encoded in two matrix equations to enable efficient data assimilation. Our simulations reveal three key limitations on the timing and capacity of in-situ CDR. First, organic acids and clay phases in fertile soils act as temporary cation sinks that delay carbonate formation after alkaline mineral additions. Second, net nitrogen acidity from fertilizer applications drives strong acid weathering that reduces in-situ CDR capacity relative to carbonic acid weathering. Third, soil temperature and excess moisture control weathering kinetics, affecting CDR accumulation rates. We validate COUSINE against field observations from a replicated ERW trial in the US Corn Belt, confirming that realized in-situ CDR is substantially lower than theoretical CDR based on rock cation depletion rates. COUSINE’s matrix simulations across diverse soils, climates, and management conditions elucidate optimal conditions for maximizing CDR and provide a science-based tool for efficacy assessment and verification.