Harvest Time and Cutting Height Influence On Biomass Yield and Quality of Young and Mature Switchgrass Stands.

Switchgrass (Panicum virgatum L.) is a native perennial prairie grass that grows in a wide range of climatic conditions and is currently being considered as a potential energy crop for biofuel. Our objectives were to develop harvest management recommendations for an upland variety of switchgrass (Cave-in-Rock). Two studies were conducted during 2009-2012 growing seasons to determine the response of a young (3-yr old) and a mature (7-yr old) switchgrass stands to time of harvest (fall, winter, and spring) and cutting height (7.5, 15 cm). Measurements taken consisted of yield, ash, total nitrogen, and mineral content in the feedstock and non-structural carbohydrates in the roots at the time of harvest. Biomass yield of young stand steadily decreased with aging whereas in mature stand the yield remained constant in three years of study. The results indicated that yield projections should not be based on the initial years of production but should be averaged over a longer period. Harvest time significantly influenced biomass yield in young stand.  Fall harvest in the first year of study resulted in highest yield however in subsequent years fall harvest had no significant advantage over other harvesting times mainly due to increased weed pressure. Reducing the cutting height down to 7.5 cm increased biomass yield in both stands by 1 Mg ha^-1. Mineral contents significantly decreased with delaying the harvest until frost (winter harvest).