WATER-QUALITY IMPACTS ASSOCIATED WITH SORGHUM CULTURE IN THE SOUTHERN PLAINS

Nonpoint-source pollution of surface water by the transport of sediment, N, and P in agricultural runoff is one of the nation's major water quality concerns. Consequently, concentrations and amounts of sediment, N, and P in runoff from Conventional Till (CT), Reduced Till (RT), and No Till (NT), sorghum [Sorghum bicolor (L.) Moench.] watersheds in the Southern Plains, were measured during a 5-yr period to evaluate water quality impacts of sorghum culture. Mean annual sediment and total N and P loss in runoff from NT (281, 0.76, and 0.28 kg ha-1 yr-1, respectively) and RT (523, 0.99, and 0.37 kg ha-1 yr-1, respectively) were lower than from CT sorghum (8877, 7.28, and 2.5 kg ha-1 yr-1, respectively). In contrast, tillage effects on soluble N and P losses were generally small and less consistent, although soluble P concentrations exceeded limits associated with accelerated eutrophication (0.01 mg L-1). Predicted losses of soluble P and particulate N and P using desorption kinetics and enrichment ratio relationships were not significantly different from measured values for all tillage practices (r2 ranged from 0.66 to 0.99). Overall, conservation tillage (NT and RT) reduced sediment, N, and P transport in runoff relative to CT and thereby lessened the potential impact of sorghum culture on surface water quality in the Southern Plains.