Challenges and Opportunities in Measuring Soil Organic Carbon Dynamics Under Enhanced Rock Weathering

The response of cropland soil organic carbon (SOC) to enhanced rock weathering (ERW) is highly variable, with the greatest potential for SOC accrual occurring in low-latitude, acidic, nutrient-poor soils. However, detecting ERW-driven changes in SOC stocks at spatial and temporal scales relevant for carbon dioxide removal remains challenging. Bulk SOC stock measurements are limited by slow rates of detectable change, high spatial variability, and substantial uncertainty introduced by bulk density measurements, which can obscure real SOC trends even when concentrations shift. Soil carbon dynamics are inherently complex, and processes that promote carbon stabilization can simultaneously stimulate SOC loss. These interacting mechanisms highlight the need for a holistic, system-level approach that accounts for both gains and losses and their temporal evolution. Evidence from mesocosm and field studies indicates that silicate rock applications can shift SOC into more stable pools through aggregation and mineral association, driven by rock-derived cations that promote particulate organic matter (POM) formation and mineral-associated organic matter (MAOM) accrual. Fraction-specific SOC analyses are more sensitive than bulk measurements in detecting such changes. To address these challenges, we are establishing highly monitored, replicated field trials designed to detect ERW-driven SOC responses using SOC fractionation. Trials are underway in sugarcane and cassava–soybean systems, with POM and MAOM to be measured pre-deployment and after one and two years. These data will support improved detection of ERW impacts on SOC, inform biogeochemical models, and advance understanding of the full carbon balance of ERW deployment.