Seasonal Time and Frequency of Switchgrass Harvest Affects Biomass Yield and Feedstock Quality.

Seasonal time of switchgrass (Panicum virgatum L.) harvest affects both yield and feedstock quality and there is interest in reducing harvest frequency to improve wildlife habitat value when using Conservation Reserve Program (CRP) land for biomass production. A field study in central Pennsylvania compared three seasonal harvest management treatments (i) summer at peak biomass (mid August), (ii) fall after frost, and (iii) in the spring after over wintering in the field, harvested either annually, every 2 yr, or every 3 yr. Annual summer and spring harvested yields were similar but 30% lower than fall yields. Biennial and triennial yields showed a different relationship; summer and fall harvested yields were similar, while spring yields were about 35% lower. Only 15 to 25% of the standing harvestable biomass was from previous year’s growth in the biennial and triennial harvest, however, residue remaining after harvest accounted for 35 to 55% of the total biomass produced. If management practices could be developed to capture this residue, the economic viability of reduced harvest frequencies could improve. Multifunctional benefits of wildlife habitat, feedstock quality, yield, and year round supply may best be met by harvesting fields over a range of seasons and frequencies.