Winter Biomass Yield and Elemental Composition of ‘Kanlow' Switchgrass in a Zero Input Environment.

Switchgrass (Panicum virgatum L.) is a warm-season perennial species native to North America. It was selected by the DOE as the model herbaceous species for development as a cellulosic feedstock crop for biofuels production. Its biomass yield is maximized in a single cut before the end of growing season. However, information is limited on biomass yield and elemental composition of standing cured biomass harvested in winter months. A wider harvest window would be beneficial to supply feedstocks for a large scale industrial biorefinery. The objectives of this study were to characterize changes in biomass yield and elemental composition of Kanlow switchgrass harvested in winter. A ca 10-year old unfertilized Kanlow switchgrass planting was used in the study. The experimental treatment was monthly harvest of standing biomass beginning in November and ending in March of the two test years completed.  Experimental design was a randomized complete block design with 6 replications, each replication being a large plot of 200 m². The 2-yr mean dry matter yield of winter harvests was 5.13 t/ha, ranging from 3.88 t/ha in 2007-2008 to 6.38 t/ha in 2008-2009. Concentrations of P, K, Mg, S, Cu, ADF and NDF in the biomass decreased with aging of the standing cured biomass, while N, C, Ca, Na, Fe, Zn, Mn, Ni, ash, and ADL content remained unaffected. A significant interaction (p<0.0001) of harvest and year was observed. A decreasing trend of biomass yield in the first winter (p<0.0001) and a constant yield in the second one (p=0.06755) were observed. Moisture content varied over the winter months with maximum in December for both years.