Daycent Simulations to Test the Influence of Nitrogen Fertilization in Bioenergy Sorghum Production.

A biogeochemical model, DAYCENT, was used to simulate the influence of nitrogen (N) fertilization on aboveground biomass carbon (C), soil organic carbon (SOC), and greenhouse gas (GHG) [carbon dioxide (CO₂) and nitrous oxide (N₂O)] emissions in bioenergy sorghum production. Compared with the simulated control (without N application), the simulated N fertilization treatment had 190.74%, 6.94%, 34.62% and 66.33% greater aboveground biomass C, 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 34.92%, 2.31%, and 10.59%, and 80.03% respectively. Though the performance of the model in simulating aboveground biomass C was reasonably accurate (r² = 0.57, slope = 0.36, intercept = 346.61, RMSE = 33.78), DAYCENT tended to underestimate crop yield when no N fertilization was applied. The model estimations of SOC were more satisfactory than aboveground biomass C (r² = 0.57, slope = 0.83, intercept = 666.43, RMSE = 10.10). DAYCENT also successfully reflected the daily GHG flux variation affected by treatments, management practices, and seasonal changes. Though both GHG annual emissions were underestimated by the model, treatment differences and yearly variation could be simulated favorably well for both CO₂ (r² = 0.71, slope = 0.65, intercept = 471.84, RMSE = 21.99) and N₂O (r² = 0.84, slope = 1.25, intercept = 1774.90, RMSE = 41.69).