Modeling nitrogen loss from switchgrass agricultural systems

A water quality modeling study was conducted to determine and compare nitrogen loss from water flow to surface water and ground water from agricultural systems growing switchgrass and cotton in the southeastern USA. 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 the loss is significantly less as the switchgrass matures. During the second year of growth the modeled nitrogen loss from switchgrass was approximately 50% that of cotton. The long term nitrogen loss over the lifetime of switchgrass was approximately 10% that of cotton. The results also indicate that the 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.

► Surface and ground water nitrogen loss comparisons for switchgrass and cotton in southern USA.
► Young switchgrass nitrogen loss comparable to cotton.
► Mature switchgrass nitrogen loss 10–15% of cotton.
► Constant emission factor not valid to estimate nitrogen loss to surface water from agricultural systems.
► Switchgrass environmentally favorable cash crop compared to cotton.