This study will apply a modeling approach to determine whether the different agricultural management practices effect on crop yield and water quality. The models were applied to investigate crop yield, water yield, sediment yield and total phosphorus transport results from the two watersheds.

The Soil and Water Assessment Tool (SWAT) and Decision Support System for Agrotechnology Transfer (DSSAT) were calibrated and validated at the Greenville watershed and the modeling study was scaled-up to Big Sunflower River Watershed (BSRW) watersheds in west north, Mississippi using the SWAT model. The effects of crop rotations, tillage management, and irrigation management on long-term soybean yield and water quality were assessed at the BSRW. The models simulated results for each scenario will be evaluated statistically using mean, correlation coefficient of determination (R²) and root mean square error (RMSE) between long-term average models simulated and field observed soybean yield data. This study helps to identify the best crop rotation, tillage management practice, or other tested scenarios that has the greatest impact on soybean yield and water quality. 

Keywords. hydrology, soybean, rainfall, soybean yield, SWAT, watersheds.