Simulating Long-Term Impact of Crop Management in Soil Organic Carbon Using Daycent Model.

Management practices that contribute to soil organic carbon (SOC) sequestration can improve the long-term productivity of soil. We present a modeling study on the long-term (80 years) impact of various crop residue and nutrient management practices on SOC dynamics in present (conventional) and alternative (no-tillage) management scenario. DayCent model was used to simulate six treatments: burning of crop residue (FB0), no burning of cop residue with 0 (NB0), 45 (NB45) and 90 (NB90) kg N ha^-1, and addition of pea vines (PV) and cattle manure (MN), in dryland winter wheat (Triticum aestivum L.)-summer fallow (WW-SF) systems at Pendleton, OR. Model performance was evaluated by comparing modeled and observed data from 1931 to 2010. The model was reasonably accurate with R² values of 0.89, 0.96 and 0.99 for the mean of observed and modeled grain yield, residue yield and SOC, respectively. The strong positive correlation (0.71 to 0.95) between observed and modeled SOC indicated that modeled followed the same pattern as observed values. The paired t-test results demonstrated no significant bias between observed and modeled SOC for five out of six treatments. DayCent projected that SOC loss was between 866 to 2192 g C m^-2 for WW-SF systems except MN, which gained 496 g C m^-2 SOC from 1931 to 2080. However, with conversion to no-tillage system from 2011onwards all treatments started to gain SOC. DayCent results revealed that conversion to no-tillage can minimize the SOC loss by 17 to 47% under different treatments besides MN where SOC gain can be increased by more than 300%. This study suggested that adaption of no-tillage system along with addition of organic amendments can improve the long-term sustainability of dryland WW-SF systems.