Abstract
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.
Highlights
There has been growing interest in renewable feedstock sources as an alternative to reduce fossil fuel demand
Row spacing, and nitrogen rate, tropical maize biomass ranged from 30 to 35 Mg ha−1 and was 15% greater than that of temperate maize, which ranged from 26 to 31 Mg ha−1 (Figure 1a)
It was reported that diverse maize hybrids yield a range from 7 to 13 Mg ha−1 stover dry matter (DM) for Corn Belt sites, with 76 cm rows and conventional plant densities that range from 74,000 to 79,000 plants ha−1 [1]
Summary
There has been growing interest in renewable feedstock sources as an alternative to reduce fossil fuel demand. Maize stover is being harvested to a limited extent for energy purposes, and further exploration is required to identify the potential of using these “residues” directly as a second generation feedstock for bioenergy [1] Germplasm such as tropical maize (maize adapted to tropical regions) has the potential to produce high amounts of non-grain biomass and might be an attractive source of cellulosic feedstock. Accounting for a wider range of regions in the U.S, commercial maize has a typical harvest index (HI) of 0.5 to 0.57, when harvested at 35% grain moisture (physiological maturity harvest) or at 15% grain moisture (grain harvest), respectively [1] This reflects the economic importance of grain yield as the main focus of maize production in the U.S at the present time
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