Long term climate change can impact on crop and water yields. Depending on the magnitude of the climate change impact, future crop yields, and water resources effects will be variable. This study is to develop scenarios by using Soil and Water Assessment Tool (SWAT) model and assess the impacts of long term crop rotations and tillage management practice on Soybean and Corn yields, water quality, and quantity. The SWAT hydrologic and crop models were setup for the Sunflower watershed (7,660 km²) within the Yazoo river basin, Mississippi Delta. Hydrologic calibration was carried out using USGS gage flow data. Hydrologic calibration and validation was carried out for the period from 2001-2010. Crop model was calibrated and validated for the same period by using Corn and Soybean yield data from the USDA experiment station, Mississippi Agricultural and Forestry Experiment Station research program and USDA- NASS county database. Both crop and hydrologic model performances will be evaluated using coefficient of determination (R²), Nash-Sutcliff Efficiency Index (NSE) and Root Mean Square Error (RMSE). Impacts of three crop-rotation scenarios (Continuous Soybean, Soybean after Corn and Soybean after Rice) will be evaluated for the 30 year period from 1980 to 2010 and economic analysis will be estimated for each scenario.

Keywords: hydrology, crop rotation, tillage management, crop yield