Simulating LONG-TERM IMPACT of CROP Management in Soil Organic Carbon Using Daycent MODEL.

Long-term productivity of soils can be improved through the agricultural management practices that contribute to organic carbon (SOC) sequestration. We used DayCent model to simulate the impact of various crop residue and nutrient management practices on SOC content, and grain and residue yield in a long-term (80 years) winter wheat (Triticum aestivum L.)-summer fallow (WW-SF) management systems in Pendleton, OR. Treatments included fall 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 cattle manure (MN) and pea vines (PV). Model performance was evaluated by comparing modeled and observed data from 1931 to 2010. We also used DayCent to predict the impact of various crop management practices on SOC for next 70 years. 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 paired t-test results demonstrated no significant bias between observed and modeled SOC under different treatments. The model show highest rate of SOC decrease in FB0 (0.6% yr-1) and an increase in MN (0.2% yr-1) from 1931 to 2010. 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. The forecast however, revealed that gain in SOC reaches its maximum capacity by 2014, slightly declines until 2018 and stays in a steady state thereafter. Our study suggested that crop residue burning or application of inorganic fertilizers alone will not maintain SOC in dryland winter wheat-fallow system and support the long-term agricultural sustainability.