Bioethanol production in the midwestern U.S. has largely focused on maize (Zea mays L.) grain for starch-based ethanol production. There has been growing interest in lignocellulosic biomass as a feedstock for biofuels. Because maize adapted to the tropics does not initiate senescence as early as temperate-adapted maize, using a tropical germplasm could improve biomass yield. This study compares the suitability of temperate and tropical maize with differing relative maturities as feedstocks for bioethanol production. Field trials were established in central Iowa during the 2014 and 2015 growing seasons. Six hybrids of different relative maturities were grown at two levels of N fertilization and two row spacings to evaluate total biomass production and feedstock quality under midwestern U.S. conditions. Total biomass, height at the final leaf collar, stem diameter at one meter above ground, and lignocellulose concentration were measured at harvest. Tropical maize was taller and had greater non-grain and total biomass production (15% more than temperate maize), while temperate maize had greater grain yield and grain starch, as well as earlier maturation. Narrower row spacing had greater biomass and grain yield. Nitrogen fertilization rate affected grain and feedstock composition. Tropical maize had lower cellulose, lignin, and ash concentrations and higher nitrogen at harvest than that of temperate maize. Conversely, temperate maize had greater ash, cellulose, and lignin concentrations. Tropical maize planted at high densities has high potential as a feedstock for bioethanol production in the U.S. Midwest.

Biofuel production in the midwestern United States has largely focused on corn (Zea mays L.) grain for ethanol production and more recently, corn stover for lignocellulosic ethanol. Tropical corn refers to corn adapted from tropical regions. Growing tropical germplasm in temperate environments is not attractive for grain yield, but shows promise for biomass production through taller and more vigorous plants with thick stems and long leaves. The comparison between tropical corn populations and their temperate adapted counterparts with a focus on biomass production has not yet been explored under Iowa growing conditions. This study refines the accuracy of the leaf collar method, and characterizes the adaptation of the populations by evaluating crop development and biomass production. Therefore, field trials were established in central Iowa during the 2014 and 2015 growing seasons. Adapted and non-adapted versions of three populations, Tuxpeño, Suwan, and Tuson, were planted at three dates to evaluate their phenology and potential for biomass production under midwestern U.S. conditions. Plant height correlated well with vegetative development and total biomass. Adapted tropical corn had advanced grain development, while non-adapted tropical corn had advanced vegetative development and greater biomass yield. Non-adapted tropical corn flowered later, had 22% greater total biomass on average (4.6 Mg ha -1 greater than adapted), and had 43% greater non-grain biomass on average, up to 20 Mg ha -1 (6 Mg ha -1 greater than adapted), while adapted populations yielded more grain. Non-adapted tropical corn has a high potential as feedstock for Gen2 biofuels in central Iowa. A gronomy J our n al • Volume 110 , I ssue 1 • 2 018 1 C orn from tropical regions is highly photoperiod sensitive; therefore, it fl owers later when grown at temperate latitudes than when grown at tropical latitudes (Ellis et al., 1992). Photoperiod sensitive corn is a short-day plant, and tassel initiation time is decreased when grown under short day conditions. Tropical corn continues vegetative growth when days are longer than the critical photoperiod and may therefore accumulate more biomass than temperate corn when grown at higher latitudes. Th e potential of tropical corn has been evaluated mainly for grain production (King et al., 1972;Oyervides-Garcia et al., 1985;Edmeades et al., 1993;Pulam, 2011). Due to lower grain yields compared to U.S. Corn Belt hybrids, tropical populations have been adapted to be a better source of germplasm for U.S. Corn Belt conditions (Hallauer, 1999;Teixeira et al., 2015).Tropical corn populations adapted to central Iowa conditions include Tuxpeño, Suwan, and Tuson. For the Tuxpeño adaptation, Hallauer (1994) formed a composite with three sources from Mexico (one short plant height, one "Puccinia sorghi resistant", and one early fl owering tropical population). For the Suwan adaptation, Hallauer (1994) used a population developed in Th ailand and selected in it for early fl owering. For the Tuson adaptation, H...