Simulating Impacts of Bioenergy Sorghum Residue Return on Soil Organic Carbon and Greenhouse Gas Emissions Using the Daycent Model.

Different residue management practices can affect carbon (C) allocation and thus soil C and nitrogen (N) turnover. A biogeochemical model, DAYCENT, was used to simulate the effects of bioenergy sorghum [Sorghum bicolor (L.) Moench] residue return on soil temperature and water content, soil organic carbon (SOC), and greenhouse gas (GHG) [carbon dioxide (CO₂) and nitrous oxide (N₂O)] emissions under bioenergy sorghum production. Coefficient of determination (r²) was used to test model performance. Coefficients of determination between the observed and simulated soil temperature, soil water content, SOC, and annual CO₂ and N₂O emissions were 0.94, 0.81, 0.75, 0.97, and 0.0057, respectively, indicating that the DAYCENT model captured the major patterns of soil environmental factors and C turnover, but was less accurate in estimating N₂O emissions. Compared with the simulated control (0% residue return), the simulated 50% residue return treatment had 7.77%, 15.12% and 1.25% greater SOC, annual CO₂ and N₂O emissions, respectively, averaged over two years’ data (2010 and 2011). Similar patterns in the simulated outputs were also observed in our field trials, with percentages being 4.52%, 15.98%, and 12.89%, respectively. The model also successfully reflected the daily GHG flux variation affected by treatments, management practices, and seasonal changes except for missing some high growing season fluxes. In addition, annual variations in the simulated outputs were comparable with field observations except the N₂O emissions in the 50% residue return treatment. Our study indicated that DAYCENT, reasonably simulated the main effects of residue return on soil C turnover, but underestimated N₂O emissions.