Measured and Cqestr Simulated Soil Organic Carbon Changes of Dryland Agroecosystem Under Climate Change Scenarios.

The potential effects of global climate change (CC) on C cycling and soil organic carbon (SOC) storage/loss in agroecosystems can be assessed by process-based models such as CQESTR. The CQESTR model was used to simulate the effect of tillage and N fertilization on SOC storage/loss in three long-term experiments under dryland wheat–fallow rotation. Using a 30 year simulation approach, the effects of biomass increases/decreases, intensifying cropping and two decades of potential CC scenarios on SOC stock under 0 and 135 kg N/ha (0N and 135N) in no-till (NT) and conventional tillage (CT) management were examined. These SOC stocks were also compared with those of a grass pasture (GP). Predicted SOC stock in the topsoil of the GP increased by 22% with a 30% increase in biomass under current climate compared to CC scenario. The topsoil was more affected by CC than the subsoil. A loss of SOC was predicted at 0-30 and 30-60 cm depths for the CT–0N in all scenarios. The same was true for the CT–135N and NT–0N, except SOC gains of 0.26 and 1.37 Mg/ha were predicted, respectively, for continuous winter wheat under CC scenarios. The NT–135N was the only treatment with SOC gains ranging from 1.35 Mg/ha, in wheat–fallow system with 30% biomass reduction, to 8.61 Mg/ha for continuous winter wheat. Relative to the GP, the C sink capacities of the NT–135N, NT–0N, CT–135N, and CT–0N were 12.69, 14.54, 13.46 and 18.57 Mg/ha, respectively. Crop intensification under NT is a viable management system which could sequester up to 1.05 Mg CO₂/ha/yr and improve SOC stock under dryland cropping systems while reducing CO₂ in the atmosphere.