Abstract
High yielding perennial grasses could integrate bioenergy-livestock operations, thereby, offsetting diversions of cropland to lignocellulosic crops, but research is needed to determine chemical composition and digestibility of leaf and stem fractions that might affect downstream reside uses. The objective of this study was to compare feedstock quality of leaf and stem tissues of dedicated bioenergy feedstocks: giant miscanthus (Miscanthus × giganteus), giant reed (Arundo donax), and miscane (Saccharum hybrid × Miscanthus spp.) when grown with or without supplemental irrigation on an upland site. Three species were space-planted on a silt loam soil in March 2007 and harvested prior to the first freeze in plant-cane, first ratoon, and second-ratoon crops for three years. Giant miscanthus leaf tissue had greatest acid detergent lignin and cellulose, and lowest concentrations of nitrogen (N) and total nonstructural carbohydrates (TNC) in ratoon crops. Giant reed leaf tissue had greatest concentrations of in vitro digestible dry matter (IVDMD), TNC, and N (P ≤ 0.05). Conversely, miscane stem tissue had greatest concentrations of IVDMD, TNC, hemicellulose, and low dry matter and combustible energy (P ≤ 0.05). Results suggest all species’ residue has positive feedstock attributes for thermochemical bioenergy conversion, and albeit giant miscanthus has very little potential value as fodder. Miscane stem and giant reed leaf tissue have potential value as livestock feed, although giant reed is not currently recommended for planting. Further research is needed on dietary composition, acceptability, voluntary intake, and live weight gain before any of these species are recommended as livestock feed sources.
Highlights
Compared with their first-generation biofuel counterparts, second-generation biomass crops require fewer inputs, produce greater energy on a landmass basis, reduce greenhouse gas emissions, and do not directly compete for arable land for food production [1] [2]
Because a large number of two and three-way interaction effects were significant, results are focused on significant three-way interactions involving species as follows: year × tissue × species for in vitro dry matter digestibility (IVDMD), acid detergent lignin (ADL), and N; and tissue × species × irrigation for total nonstructural carbohydrates (TNC), cellulose, and gross energy density
Lignin is high in combustible energy, similar to that of cellulose [38], and the values we found should not cause excessive tar production during gasification [39]
Summary
Compared with their first-generation biofuel counterparts, second-generation biomass crops require fewer inputs, produce greater energy on a landmass basis, reduce greenhouse gas emissions, and do not directly compete for arable land for food production [1] [2]. In order to transform the forage-livestock industry towards second-generation biofuels without affecting grassland resources for animal operations, identifying dual-use perennial forage feedstocks is key. Small commercial farms, those with gross cash farm income from $10,000 to $249,999, account for 36% of all farms and 22% of total agricultural production in the US, but they are challenged to remain profitable [4]. A new market for grassland agriculture is emerging because the Energy Independence and Security Act will require 36 billion gallons of renewable fuels by 2022 [5] To meet this goal, an estimated 1 billion Mg∙yr−1 dry lignocellulosic biomass would be converted to renewable, liquid biofuels [6]
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