Harvest Management and Nitrogen Application Rate Influence On Biomass Yield, Quality and Nitrogen-Use Efficiency of Switchgrass Grown for Combustion.

Producing high-yielding switchgrass (Panicum virgatum L.) with premium biofuel quality and simultaneously maintaining the crop health is challenging. A three-year study was conducted at the Crops and Animal Research and Education Farm of the University of Massachusetts in South Deerfield, MA during the 2009-2012 growing seasons to evaluate harvest management and N application rates influence on biomass yield, mineral content of the grass, non structural carbohydrate (NSC) reserves in the roots, as well as nitrogen-use efficiency (NUE) of switchgrass (cv. Cave-in-Rock) grown for combustion. Delaying harvest from fall until spring reduced the biomass yield. Highest biomass production was obtained from fall harvest in the first growing season. Decreasing the cutting height from 15 to 7.5 cm resulted in higher biomass production but had no influence on nutrient content in the above-ground biomass and NSC in the roots and crowns. Increasing N application rate up to 134 kg ha^-1 resulted in higher biomass production in the fall harvest. Nutrient concentrations and removal were significantly higher when biomass was harvested in fall compared with winter and spring. The highest NSC was measured from winter harvest which was significantly higher than those in the fall and spring.  Higher NUE was calculated with lower N application rate (67 kg N ha^-1) compared with 134 kg N ha^-1.