Crop Biomass, Soil Carbon, and Nitrous Oxide as Affected by Management and Climate: A DayCent Application in Brazil

A current national research priority in Brazil is the assessment of potential climate change impacts in agriculture. In this study, the DayCent model was used to predict changes in crop biomass, soil C stocks, and N2O fluxes of a major agricultural area in Brazil. The model was calibrated and validated using datasets from 30-yr-old experiments. Simulations of current and alternative management practices to 2100 using IPCC climate scenarios A2 and B1 were conducted. Predicted crop biomass increases ranged from 5% (sorghum [B1]) to 65% (soybean [A2]). DayCent simulated higher soil organic carbon stocks in the wheat-soybean system (VAL1) than in the wheat-soybean-vetch-sorghum system (VAL2) in both climate scenarios. Soil organic carbon accumulation by 2100 (+/- 16 Mg C ha(-1) above current 46 Mg C ha(-1)) was forecast in cropping systems with pastures (Cynodon sp.), regardless of the climate scenario. Daily N2O fluxes were underestimated by +/- 41% (0.85 g N-N2O ha(-1) d(-1)) in VAL1 and overestimated by 17.5% (0.28 g N-N2O ha(-1) d(-1)) in VAL2. Cumulative N2O fluxes produced mixed results, which were 29% lower than observed in VAL1 and 5% higher in VAL2 but within the range of values reported in other greenhouse gas studies in southern Brazil. Simulations of N2O fluxes to 2100 with IPCC climate change scenarios B1 and A2 in southern Brazilian indicated higher annual fluxes across the alternative treatments tested in comparison to current fluxes. According to model predictions, climate change would lead to larger relative increases in N2O emissions from no-tillage (27% in B1 to 41% in A2), but these enhanced fluxes would still be lower than those from tillage by approximately 25%.