Nitrogen and Harvest Impact on Biomass Yield of Established Switchgrass.

Switchgrass (Panicum virgatum L.) has been identified as the model herbaceous biomass energy crop by the United States Department of Energy as it is capable of being a viable bioenergy feedstock while providing multiple environmental benefits when grown on marginal soil landscapes. Nitrogen (N) fertility and harvest management are crucial practices which affect both the quantity and the quality of the biomass produced. The objective of this research was to quantify the impact of N fertilizer rate and timing along with harvest date on switchgrass biomass dry matter (BDM).  Research was conducted on a total of four field-plot locations found in central and west-central Missouri. Nitrogen fertilizer was applied using dry ammonium nitrate at the rates of 0, 34, 67, and 101 kg ha^-1 at two application times, all N early spring and split N (early spring and following 1^st harvest). Harvest treatments were as follows: 1) one cut in September; 2) one cut in November; 3) one cut in June and a second in September; and 4) one cut in June and a second in November. These treatments were arranged in a split-plot design with N rate as the main plot and harvest as the sub-plot in a randomized complete bock design. Harvest date significantly affected yield at all four locations, but in a different way. At two locations highest BDM came from one harvest in November, while at the other two locations the highest BDM came from the June + November harvest strategy. Split application of N at the rate of 101 kg ha^-1 resulted in the highest BDM yield in all locations. Interactions of N rate and harvest date were location dependent and complex. Results of this research suggest that both N fertilization and harvest management need to be simultaneously considered when optimizing switchgrass growth for bioenergy.

Keywords: bioenergy, feedstock, nitrogen fertility