Abstract
Miscanthus is an intriguing cellulosic bioenergy feedstock because its aboveground productivity is high for low amounts of agrochemical inputs, but soil temperatures below −3.5°C could threaten successful cultivation in temperate regions. We used a combination of observed soil temperatures and the Agro-IBIS model to investigate how strategic residue management could reduce the risk of rhizome threatening soil temperatures. This objective was addressed using a historical (1978–2007) reconstruction of extreme minimum 10 cm soil temperatures experienced across the Midwest US and model sensitivity studies that quantified the impact of crop residue on soil temperatures. At observation sites and for simulations that had bare soil, two critical soil temperature thresholds (50% rhizome winterkill at −3.5°C and −6.0°C for different Miscanthus genotypes) were reached at rhizome planting depth (10 cm) over large geographic areas. The coldest average annual extreme 10 cm soil temperatures were between −8°C to −11°C across North Dakota, South Dakota, and Minnesota. Large portions of the region experienced 10 cm soil temperatures below −3.5°C in 75% or greater for all years, and portions of North and South Dakota, Minnesota, and Wisconsin experienced soil temperatures below −6.0°C in 50–60% of all years. For simulated management options that established varied thicknesses (1–5 cm) of miscanthus straw following harvest, extreme minimum soil temperatures increased by 2.5°C to 6°C compared to bare soil, with the greatest warming associated with thicker residue layers. While the likelihood of 10 cm soil temperatures reaching −3.5°C was greatly reduced with 2–5 cm of surface residue, portions of the Dakotas, Nebraska, Minnesota, and Wisconsin still experienced temperatures colder than −3.5°C in 50–80% of all years. Nonetheless, strategic residue management could help increase the likelihood of overwintering of miscanthus rhizomes in the first few years after establishment, although low productivity and biomass availability during these early stages could hamper such efforts.
Highlights
The recent push towards developing new bioenergy cropping systems has focused on identifying highly productive plants – other than Zea mays – to provide biomass for lignocellulosic biorefineries [1]
We briefly review two other well validated models (HYDRUS and Simultaneous Heat And Water (SHAW)) that are often used to study the impacts of agricultural management on soil heat and water flow and offer reasoning why Agro-Integrated Biosphere Simulator (IBIS) was selected to carry out the study objectives
Compared with a previous version of IBIS that was executed over the Midwest with different climate and soils datasets at coarser spatial resolution [30], Agro-IBIS simulations exhibited increased snow depth in all months from December through March for the potential (natural) vegetation (POTVEG) scenario, which is how land cover in Lenters et al [30] was parameterized
Summary
The recent push towards developing new bioenergy cropping systems has focused on identifying highly productive plants – other than Zea mays (maize) – to provide biomass for lignocellulosic biorefineries [1]. One of the plants of interest, miscanthus, is a highly productive C4 perennial rhizomatous grass, which is not native to many temperate regions, but its bioenergy potential is being studied extensively in Europe, the US, and Canada [3,4,5]. In the Midwest US, Miscanthus 6 giganteus is being studied as a model cellulosic feedstock because for low amounts of agrochemical inputs, its productivity is extremely high, ,60% higher than maize total aboveground biomass [5], and double that of another C4 grass contender, switchgrass (Panicum virgatum), regardless of climate and nitrogen fertilizer applied [6]. Because the triploid M. 6 giganteus clones are sterile, establishment results from the planting of rhizomes at a typical depth of 5 to 10 cm [10], and is more costly to establish on the basis of time and money [11]
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