Water Quality Impacts of Bioenergy Crops Grown on Marginal Land.

Perennial warm season grasses (WSGs) provide biofuel feedstocks and could improve soil ecosystem services including water quality. However, there is limited information on water quality impact of WSGs when grown on marginal lands. We studied how perennial WSGs and no-till corn grown on marginally productive croplands impacted runoff, and sediment and nutrient losses. The experiment was conducted on silty clay loam soils in south western Iowa and east central Nebraska. Treatments studied were switchgrass and no-till continuous corn at the Iowa site, and Liberty switchgrass, Shawnee switchgrass, low diversity WSGs mixture and a corn-soybean rotation at the Nebraska site. Rainfall was simulated for 1 h at an intensity of 63.5 ± 2.8 mm h^-1 in spring 2017, and water quality parameters were measured. We observed no difference in time to runoff start and runoff volume among the bioenergy crops at either site. Switchgrass, however, tended to increase time to runoff start relative to the corn. We are currently analyzing soil properties to understand their interrelationships with water quality parameters. Sediment, and NO₃-N, NH₄-N, Ortho P and total P losses were consistently higher in corn than in switchgrass cultivars at the Nebraska site. Residue cover at the Nebraska site was significantly higher in switchgrass cultivars than in corn and dissolved nutrients were negatively correlated with residue cover. Corn lost 0.72 ± 0.54 Mg ha^-1 of sediment and 2.4 ± 0.16 kg ha^-1 of NO₃-N through runoff water at the Nebraska site. Low diversity mixture of switchgrass showed higher potential to improve water quality parameters compared to corn and monoculture of WSGs. Overall, growing WSGs show potential to improve water quality in marginally productive croplands.