Biomass Production and Nutrient Removal by Switchgrass (Panicum virgatum) under Irrigation.

Perennial herbaceous bioenergy crops have the potential to improve soil quality, sequester soil C, enhance nutrient cycling improve wildlife habitat, and supply a portion of U.S. energy needs when used as a fuel. Assessments of the export of essential plant nutrients are needed to determine impacts on soil fertility that will influence fertilizer recommendations since the nutrients contained in the above ground biomass will be removed from the field when processed as a bioenergy feedstock. The objective of this study was to determine the biomass production, nutrient concentration and response of switchgrass to N fertilization grown under irrigation. This research showed that switchgrass (Panicum virgatum) production in the warmer irrigated regions of the PNW was a viable bioenergy feedstock with aboveground biomass yields averaging 20.4 16.9 and 14.5 Mg dry matter ha^-1 y^-1 for Kanlow, Shawnee, and Cave in Rock cultivars, respectively. The annual export of macronutrients from the field averaged 214 kg N ha^-1, 40 kg P ha^-1, 350 kg K ha^-1, 15 kg S ha^-1, 60 kg Ca ha^-1, 38 kg Mg ha^-1, and 6 kg Fe ha^-1 among cultivars.  Switchgrass required 1kg of N to produce 83 kg of biomass. Micronutrients (B, Mn, Cu, and Zn) removed at harvest averaged less than 1 kg ha^-1 among cultivars.  Root biomass produced after three seasons, averaged 9.2 Mg ha^-1 to a depth of 1 m.