Effect of the Sugarcane Ripener Glyphosate (Roundup PowerMAX® II) on Agronomic and Biomass Characteristics of Energy Cane.

Energy cane (Saccharum spp.,) is a very promising feedstock for renewable and carbon-neutral energy production because of its high-yield potential and wide environmental adaptability. Besides yield, feedstock quality is critical for conversion efficiency at processing facilities. The objective of this study was to determine if sugarcane ripeners, used in enhancing sugar production in sugarcane, could have a similar function in altering biomass characteristics of energy cane. Forty-two energy cane clones were evaluated in the first ratoon cane crop at St. Gabriel, Louisiana in a randomized complete block design with six replications. Three replications were sprayed with glyphosate at 950 g (a.i.) ha^-1 in September 2016 and the entire experiment was harvested in October, 2016. Compared to controls, Glyphosate treatment significantly reduced (P>0.05) biomass moisture (67.8 vs. 69.4%) and fiber (16.6 vs. 17.3%) contents. However, treatments had no significant effects on fresh (48.9 vs. 44.7 Mg·ha^-1) or dry (15.7 vs. 13.5 Mg·ha^-1) biomass yield. Total recoverable sugars (82.9 vs. 62.9 kg·Mg^-1) and sugar yield (4.1 vs. 2.8 Mg·ha^-1) increased significantly following glyphosate application. Although at the population level fiber component traits such as cellulose (38.66 vs. 38.79%), hemicellulose (21.73 vs. 21.62%), lignin (17.67 vs. 17.76%) and adjusted total cellulosic fiber (total of cellulose, hemicellulose and lignin) (78.0.6 vs. 78.2%) contents were unaffected by glyphosate treatment, it was possible to select individual clones in which these traits were significantly altered. In addition, 13 of the evaluated clones surpassed the adjusted cellulosic content threshold of ≥ 75% mandated by United States Environmental Protection Agency (EPA). Estimated ethanol yields were increased by 13.1% (6412 vs. 5669 L·ha^-1) following glyphosate treatment. This study demonstrated that, much like in sugarcane, ripeners can be a management tool to improve biomass characteristics of energy cane and the ultimate sustainability/profitability of renewable energy production.