Dedicated Bioenergy Crops and Water Quality.

Crop residues are candidates as renewable feedstocks for cellulosic biofuel. However, residue removal at high rates may increase loss of sediments and nutrients in runoff, negatively affecting water quality. Perennial warm season grasses (WSGs) and short-rotation woody crops (SRWCs) could be a better alternative to crop residues as dedicated bioenergy feedstocks to improve water quality. However, our understanding of the impacts of dedicated bioenergy crops on water quality is limited. We reviewed available information on the potential impacts of dedicated bioenergy crops on water quality, and identified research gaps and opportunities of growing dedicated bioenergy crops. The reviewed studies indicate that crop residue removal at rates >50% (residue retention up to 4.71 Mg ha^-1) can increase runoff by 7 to 27 mm, sediment loss by 0.3 to 13.5 Mg ha^-1 and NO₃-N by 0.85 to 2.06 kg ha^-1 per rainfall event. Few have studied impacts of growing WSGs as dedicated bioenergy crops on sediment and nutrients losses. However, WSGs can reduce up to 97% sediment and 94% of dissolved nutrients, when used as vegetation barriers and filter strips. This indicates that if WSGs were grown as dedicated bioenergy crops, they could significantly improve water quality. Published studies also indicate that SRWCs can reduce water erosion. Marginal lands and center pivot corners were identified as potential land areas for growing dedicated energy crops. Further work should focus on 1) field data collection from energy crops grown on marginal lands, 2) growing monoculture or polyculture WSGs for energy, 3) land use planning for large-scale production of WSGs and SRWCs and 4) modeling using measured data. Overall, growing WSGs and SRWCs could reduce losses of non-point source pollutants compared to crop residue removal, but more field studies are needed to fully understand their extent of the benefits on water quality.