Modeling nitrogen loss from regional switchgrass agriculture

A water quality modeling study was conducted to determine and compare nitrogen loss from agricultural systems growing switchgrass and cotton in the southeastern USA. The water quality impacts were modeled at the plot scale and at the watershed scale. The Soil and Water Assessment Tool (SWAT) was used to replicate field conditions observed at switchgrass research plots at Pee Dee Research and Educational Center at Florence, South Carolina. The plot scale modeling suggested that in the early years of growth there is significant nitrogen loss from switchgrass to streamflow and groundwater but they are significantly less as the switchgrass matures. The long-term nitrogen loss over the lifetime of switchgrass was approximately 10% that from cotton. The watershed-scale modeling was carried out for the Black Creek watershed located in the Pee Dee River basin in South Carolina. The results were even more encouraging than those for the plotscale modeling. The long-term loss of nitrogen was approximately 1% that from cotton when switchgrass was grown on all cotton farms in the watershed, according to the simulations. The results also indicate use of computational models to quantify nitrogen fluxes in Life Cycle Assessment (LCA) of agricultural systems growing switchgrass gives a more accurate representation of the system than using constant emission factors.