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Abstract
Three agricultural non‐point source (NPS) models, GLEAMS, EPIC, and WEPP, were used to simulate the effects of two tillage systems on runoff and losses of sediment, N, and P from a field‐sized watershed in the Tennessee valley region of Alabama. The field was cultivated with three years of conventional tillage (CvT) followed by three years of conservation tillage (CsT) of cotton. GLEAMS and EPIC underpredicted NO3‐N losses in runoff for both tillage systems. EPIC simulated tillage effects on soluble‐P losses better than GLEAMS. However, EPIC poorly predicted annual organic‐N and P losses in sediment, mainly due to overpredicted sediment losses. The GLEAMS prediction of annual organic‐N and P losses in sediment was more acceptable than that of EPIC. WEPP predicted sediment losses close to observed data for both tillage systems. However, EPIC simulation of sediment loss was not as accurate, because its limited definition of watershed profile prevented the model accounting for sediment deposition on the watershed depressional area.