Empirical geographic modeling of switchgrass yields in the United States

Abstract

Switchgrass (Panicum virgatum L.) is a perennial grass native to the United States that has been studied as a sustainable source of biomass fuel. Although many field-scale studies have examined the potential of this grass as a bioenergy crop, these studies have not been integrated. In this study, we present an empirical model for switchgrass yield and use this model to predict yield for the conterminous United States. We added environmental covariates to assembled yield data from field trials based on geographic location. We developed empirical models based on these data. The resulting empirical models, which account for spatial autocorrelation in the field data, provide the ability to estimate yield from factors associated with climate, soils, and management for both lowland and upland varieties of switchgrass. Yields of both ecotypes showed quadratic responses to temperature, increased with precipitation and minimum winter temperature, and decreased with stand age. Only the upland ecotype showed a positive response to our index of soil wetness and only the lowland ecotype showed a positive response to fertilizer. We view this empirical modeling effort, not as an alternative to mechanistic plant-growth modeling, but rather as a first step in the process of functional validation that will compare patterns produced by the models with those found in data. For the upland variety, the correlation between measured yields and yields predicted by empirical models was 0.62 for the training subset and 0.58 for the test subset. For the lowland variety, the correlation was 0.46 for the training subset and 0.19 for the test subset. Because considerable variation in yield remains unexplained, it will be important in the future to characterize spatial and local sources of uncertainty associated with empirical yield estimates.

U.S. Billion-Ton Update: Biomass Supply for a Bioenergy and Bioproducts Industry

“…Sources: Wullschleger et al, 2010;Jager et al, 2010 Summary of Production Inputs and Costs for Woody Crops , pine, and willow are $43-$47, $43-$46, and $38-$45 …”

Estimates of Biomass Yield for Perennial Bioenergy Grasses in the USA

“…A number of crop productivity modeling studies have estimated the biomass yields for Miscanthus and switchgrass in the USA. For example, Jager et al [9] have developed empirical models to estimate yield from factors associated with climate, soils, and management for both lowland and upland switchgrass cultivars. However, these model estimates are usually limited by available observation data from field trials and have limited representation of diverse climate, soil, and topographical conditions across the USA [10].…”

Using satellite vegetation and compound topographic indices to map highly erodible cropland buffers for cellulosic biofuel crop developments in eastern Nebraska, USA

“…Because switchgrass is highly productive (and more productive when fertilizers and chemicals are applied to encourage its growth as a dense monoculture) and has higher biomass production than most grassland species, the total estimated switchgrass biomass productivity was assumed to be double that of the total estimated grassland biomass productivity based on previous study results ( Anderson-Teixeira et al, 2012;Behrman et al, 2012;Bonin and Lal, 2014;Fike et al, 2006;Jager et al, 2010;Kiniry et al, 2008;McLaughlin et al, 2006;Schmer et al, 2010;Tulbure et al, 2012;Vogel et al, 2002;Wullschleger et al, 2010).…”