The Impact Of Harvest Timing On Biomass Yield From Native Warm-Season Grass Mixtures

Interest in using native warm-season grasses (NWSG), especially switchgrass (SG) (Panicum virgatum L.), as a biomass crop has increased due to the focus on renewable energy sources. There is the potential to utilize the early growth of these plants as a forage crop (i.e., hay), allowing the regrowth to be harvested as a fibrous biomass crop. The three species treatments were SG, a two-way blend of big bluestem (Andropogon gerardii V.) and indiangrass (Sorghastrum nutans L.) (BB+IG), and a three-way mixture of SG, BB, and IG (SG+BB+IG). Harvest treatments were a harvest (BH) in late fall (for biomass), early-boot harvest (for forage) followed by BH (EB+BH), or early-seedhead harvest (for forage) followed by BH (ESH+BH). Delaying harvest from EB to ESH increased forage yield by 22% (P < 0.001). The SG and SG+BB+IG produced greater forage yield (averaged across both early harvest treatments) than BB+IG (10.1 and 9.1 vs. 5.5 Mg DM ha(-1), respectively; P < 0.001). Across all NWSG treatments, biomass yield was reduced by 51% for EB+BH and 68% for ESH+BH compared to BH (P < 0.001). Total yield (forage+biomass) was greatest for ESH+BH with both SG and SG+BB+IG, whereas the mixture of SG+BB+IG provided the greatest total annual yield, 20.1 Mg DM ha(-1) (P = 0.002). These results suggested that NWSG, grown in the mid-South United States under a dual-harvest system, can increase harvest options for producers by supplying acceptable forage yield for both early harvests and still provide biomass production.