The impact of harvest timing on biomass yield from native warm-season grass mixtures
McIntosh, D., G. E. Bates, P. D. Keyser, F. L. Allen, C. A. Harper, J. L. Birckhead, J. C. Waller, W. M. Backus, and J. E. Beeler.  2015.  Agronomy Journal, 107:2321–2326.

Abstract:
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.