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

2321 The development of renewable energy sources has become an issue of increasing importance and consequently has grown over the last three decades (Lynd et al., 1991; Sanderson et. al., 1996; McLaughlin and Kszos, 2005). It has been estimated that more than 21 million ha of SG might be needed annually for biomass production (English et al., 2006). If SG or other dedicated herbaceous energy crops were planted at this scale, there could be a significant portion of land currently being used for forage production being displaced by biomass crops (English et al., 2006; Graham et al., 2008; Sanderson and Adler, 2008). To address this issue, dualharvest forage/biomass systems have been explored with interest in using SG for biomass (Sanderson et al., 1999; Guretzky et al., 2011; Mosali et al., 2013). This approach could allow producers the flexibility to divert some biomass production into forage, exploit biomass markets, select alternative harvest options, and the potential to increase profitability (Sanderson and Adler, 2008). Where forage is a priority, growing-season harvests should occur earlier in the growing season when forage has a higher nutritive value (Mitchell et al., 2001; Guretzky et al., 2011; Richner et al., 2014). Several studies have examined dualharvests (i.e., growing-season plus dormant-season) in SG but those harvests occurred in late June or mid-July, when plants had flowered and nutritive value had fallen below optimum levels (Grabowski et al., 2004; Thomason et al., 2005; Fike et al., 2006; Guretzky et al., 2011). In the southern Great Plains, Sanderson et al. (1999) concluded a May/dormant harvest combination was the best approach for a dual-harvest system. In another study from the southern Great Plains, Guretzky et al. (2011) recommended dual-harvest use of SG if the first harvest was taken early in the growing season and the biomass harvest was taken after the first killing frost. In the northern Great Plains, Vogel et al. (2002) recommended an early harvest Climatology & Water Management