Nonpoint source pollution has been identified as one of the major sources of pollution of surface water bodies in Iowa and the Midwest. GLEAMS (Version 2.1) model was calibrated and validated using three years (1990-92) field data on nitrate-nitrogen (NO3-N) and herbicide concentrations in subsurface drain water. GLEAMS model was calibrated for chisel plow system and was validated for chisel plow, moldboard plow, ridge till and no-till systems based on measured tile flows, nitrate-nitrogen (NO3-N), atrazine, and alachlor losses with tile flows, N-uptake and other biomass parameters. The nutrient component of the GLEAMS model was calibrated using steady state N-pool values obtained after multiple years of model runs. The results of this study has demonstrated that GLEAMS model has the potential to simulate tillage effects on tile flow, leaching losses of NO3-N, atrazine, and alachlor with tile flows, N-uptake and biomass parameters within 10% difference of the measured values.