Agronomic Management of Switchgrass for Optimizing Quality and Digestibility for the Bioconversion Platform.

Switchgrass (Panicum virgatum L.), a native, warm-season grass, has been identified as a model herbaceous perennial crop for cellulosic ethanol production by the U.S. Department of Energy. Agronomic management specific to the Great Lakes Region is needed for producing switchgrass in an economically and environmentally sustainable manner for the bioconversion platform. A field study was conducted to determine the best agronomic N rate and harvest management system for optimizing switchgrass yield and quality as a bioenergy feedstock. The experiment was a randomized complete block design with five replications, and consisted of three harvest management systems (one- cut fall, one-cut overwintered, and a two-cut system), and four N rates (0, 39, 78 and 157 kg N ha-1). Acetyl bromide soluble lignin increased with maturity, with a corresponding decline in digestibility. Crystalline cellulose content was highest when allowed to mature with single- cut harvest management. Hemicellulose composition varied with harvest management; xylose was highest in the summer, and rhamnose, arabinose and mannose levels decreased with increasing applied nitrogen fertilizer. A single harvest made in the fall after a killing frost was found to be the best harvest management system, with a mean yield of 12.3 Mg ha-1. Biomass yields did not differ between 78 and 157 kg N ha-1 indicative of a yield plateau. The yield response to N was best modeled with a linear response plateau.