Forage Harvest Timing Impact on Biomass Quality from Native Warm-Season Grass Mixtures

Biomass production systems using native warm-season grasses can allow for an early-season harvest (for forage) followed by a dormant harvest (for biomass). A study was conducted to investigate the impact of harvest timing and grass species on the chemical composition of harvested forage and biomass. The three-species composite treatments were switchgrass (SG) (Panicum virgatum L.); a two-way blend of big bluestem (Andropogon gerardii V.) (BB) and indiangrass (Sorghastrum nutans L.) (IG); and a three-way mixture of SG, BB, and IG. Harvest treatments were a biomass harvest (BH) in late fall, early-boot (EB) harvest (for forage) followed by BH, or early-seedhead harvest (ESH) (for forage) followed by BH. Forage harvested at EB had greater crude protein and less neutral detergent fiber (NDF) and acid detergent fiber (ADF) compared with ESH (P = 0.05). The ADF and NDF content of biomass was greatest for BH and was reduced in biomass regrowth after EB, with the later ESH resulting in the largest decrease in fiber content. Total macronutrient removal of N, P, and K was increased in the dual-use system. Results indicated that it is possible to alter the composition of biomass provided for bioenergy production by taking an early-season forage harvest.