Simulated Soil Organic Carbon Changes in Maryland Are Affected by Tillage, Climate Change, and Crop Yield

The impact of climate change on soil organic C (SOC) stocks in no‐till (NT) and conventionally tilled (CT) agricultural systems is poorly understood. The objective of this study was to simulate the impact of projected climate change on SOC to 50‐cm soil depth for grain cropping systems in the southern Mid‐Atlantic region of the United States. We used SOC and other data from the long‐term Farming Systems Project in Beltsville, MD, and CQESTR, a process‐based soil C model, to predict the impact of cropping systems and climate (air temperature and precipitation) on SOC for a 40‐yr period (2012–2052). Since future crop yields are uncertain, we simulated five scenarios with differing yield levels (crop yields from 1996–2014, and at 10 or 30% greater or lesser than these yields). Without change in climate or crop yields (baseline conditions) CQESTR predicted an increase in SOC of 0.014 and 0.021 Mg ha −1 yr −1 in CT and NT, respectively. Predicted climate change alone resulted in an SOC increase of only 0.002 Mg ha −1 yr −1 in NT and a decrease of 0.017 Mg ha −1 yr −1 in CT. Crop yield declines of 10 and 30% led to SOC decreases between 2 and 8% compared with 2012 levels. Increasing crop yield by 10 and 30% was sufficient to raise SOC 2 and 7%, respectively, above the climate‐only scenario under both CT and NT between 2012 and 2052. Results indicate that under these simulated conditions, the negative impact of climate change on SOC levels could be mitigated by crop yield increases. Core Ideas Soil organic C was greater in a no‐till than a conventional tillage system. CQESTR model‐simulated soil organic C increased under both systems. CQESTR‐simulated soil organic C decreased under climate change. Simulated soil organic C decreased under climate change when yields were reduced. Simulated soil organic C increased under climate change when yields were increased.