Soil Organic Carbon Improves Crop Yield and Yield Resilience

Increasing soil organic carbon (SOC) has been proposed as a strategy to promote crop yield resilience under extreme hydroclimatic stress, particularly drought, due to its positive effect on soil available water-holding capacity. We analyze how SOC mediates the relationship between US rainfed crop yields (1981-2020) and growing season hydroclimatic conditions-defined by soil water supply and atmospheric water demand-over 67,000 county-years across three major crops. We show that higher SOC is consistently associated with increased crop yields and yield resilience, evidenced through reduced interannual variability. Contrary to prevailing expectations, the largest yield gains from SOC occur during moderate water supply conditions-not drought. Under drought, water supply to crops may be more limited by water inputs to soil than by soil water-holding capacity, constraining the benefit provided by SOC regeneration. Furthermore, because moderate conditions are more frequent than drought or wet extremes, the largest production gains from SOC accumulate under moderate conditions. These findings indicate that SOC regeneration can enhance drought resilience to some degree but cannot compensate for extreme water scarcity; the services SOC provides to crops, including water storage, require water for their effective delivery.