Comparison of Measured and Modeled Affects of Residue Removal on Soil Organic Carbon.

Soil organic carbon (SOC) is an important soil property strongly influenced by management. Changes in SOC are difficult to measure through direct sampling requiring long time periods and intensive sampling to detect small changes in the large, highly variable pool. Models have the potential to predict management induced changes in SOC but require long-term data sets for validation. CQESTR is a processed-based model that uses site weather, management, and crop data to estimate changes in SOC. Crop residue removal for livestock feed or future biofuel feed stock use is a current management practice potentially affecting SOC. CQESTR estimated changes in SOC were compared to measured changes for two residue removal studies in eastern NE. The rainfed site compared SOC changes in no-tillage continuous corn grown under two N-rates (135 and 202 kg ha^-1) and two residue removal rates (none and 50%). The irrigated site compared SOC changes in continuous corn grown under no-tillage or disk tillage and three residue removal rates (none, 50 and 80%). After 10 years under these management scenarios CQESTR estimated SOC agreed well with measured SOC (r² = 0.93 at the rainfed site and r² = 0.82 at the irrigated site). These results are consistent with other CQESTR validation studies.