Simulating long-term soil carbon storage, greenhouse gas balance, and crop yields in semi-arid cropping systems using DayCent model

Crop-fallow systems are common in the arid and semi-arid Southwestern USA. The long fallow periods between crops reduce annual carbon (C) inputs and soil organic carbon (SOC) accumulation. Cover cropping is promoted to reduce the fallow period and increase residue C returned to the soil, but the long-term SOC sequestration and greenhouse gas (GHG) mitigation potential of cover cropping are not well understood for dry regions. This study quantifies long-term changes in SOC sequestration and net greenhouse gas (GHG) balance using the DayCent ecosystem model. We estimated SOC storage and nitrous oxide (N2O) and methane (CH4) emissions in no-till winter wheat (Triticum aestivum L.)-sorghum (Sorghum bicolor L. Moench)-fallow rotations with pea (Pisum sativum L.) and oat (Avena sativa L.) as cover crops and no-cover crop control. The DayCent simulation results on crop yields were evaluated with six years of observations and achieved R2 values of 0.66 and 0.81 for wheat grain and biomass yields, respectively. Similarly, the model captured the overall differences in cover crop biomass production. The simulations conducted for three decades showed a significantly greater SOC storage with cover cropping (26-36%) than without cover crops. Simulation of GHG emissions showed that oats as a cover crop could mitigate N2O emissions compared to control. Soil N2O emissions were greater with peas than with other cover crops, suggesting a smaller contribution of legume cover crops in reducing net GHG balance. Cover cropping could be a good strategy for long-term SOC storage in semi-arid regions, while their GHG mitigation potential varied with cover crop species.