Optimizing Cellulose Content and Yield of Switchgrass Grown as a Bioenergy Crop On a Fine-Loamy Michigan Alfisol.

Switchgrass (Panicum virgatum), a C₄ perennial grass has been selected as a suitable bioenergy feedstock for marginal land in the United States by the Department of Energy and the Great Lakes Bioenergy Research Center. The objective of this study was to estimate the effect of nitrogen fertility rates and harvest timing on switchgrass yield and the cellulosic content of the harvested biomass on a fine-loamy Michigan Alfisol. The cultivar ‘Cave-in-Rock' was established in a RCBD and uniformly harvested in 2007. Four different nitrogen rates (0, 39, 78, and 157 kg N ha^-1) were applied to the plots that were then harvested using one of three types of harvest strategies: 1) a two-cut system (anthesis and post-senescence); 2) one late fall cutting; or, 3) one early spring cut after the switchgrass had overwintered in the field. Nitrogen fertility rate was not found to be a significant factor in determining yield at the conclusion of the second growing year. Cellulose content was found to be significantly different at various nitrogen rates and harvest timings although there was no interaction between the two factors. Cellulose content was optimized under an overwinter-early spring harvest and at an N rate of either 157 kg ha^-1 or 39 kg N ha^-1. The second highest rate, 78 kg N ha^-1 was significantly lower than both the 39 kg N ha^-1 and 157 kg ha^-1 and not statistically different from the 0 kg ha^-1 N treatment. Although the overwinter-early spring harvest moisture values were at least 20% lower than all other harvest treatments a significant yield loss of 40% was incurred. Further examination of the crude protein levels and lignin content is being conducted and the study will continue in an effort to develop agronomic recommendations on producing switchgrass as a bioenergy crop for growers in the Great Lakes agroecoregion.