Abstract
AbstractUnited States mandated the production of biofuel from lignocellulosic feedstocks. Nonetheless, the cultivation of these feedstocks may produce debates, as agricultural land is scarce and it is primarily needed for food production and grazing. Thus, it is thought that biofuel production should be placed on land with low economical value (i.e., marginal land). At the same time, depending on what land is considered marginal and therefore available for lignocellulosic crops, different greenhouse gas impacts will be generated upon land use change. Here, we attempted to estimate the biomass production and soil greenhouse gas emissions of the cultivation of switchgrass (Panicum virgatum L.) and giant reed (Arundo donax L.) in the U.S. Southeast, when converting distinct former land uses. We employed the NLCD and the SSURGO databases to select grasslands, shrublands, and marginal croplands and to then allocate switchgrass and giant reed on this land basing on biophysical parameters included in the Land Capability Classification. After calibration, the DAYCENT model was employed to simulate 15‐year cultivation of both crops in the U.S. Southeast. Florida, Georgia, Mississippi and South Carolina were the States with the highest availability of land, thus the highest potential for biofuel production. Among scenarios, the one converting poor grazing land and marginal croplands yielded the greatest benefits: converting 3.6 Mha of land, 44 Mt/year of dry biomass could be produced, storing 0.05 Mt/year of soil organic C at the same time. In this scenario, considering 80‐km supply areas, nineteen biorefineries could deliver 7,124 Ml/year of advanced ethanol across the region. When minimizing giant reed invasion risks through reallocating giant reed outside flooded areas, 4,695 Ml/year of advanced ethanol could be still delivered from thirteen biorefineries, but the scenario turned in a biogenic greenhouse gas source (3.2 Mt CO2eq/year).
Highlights
Despite a more difficult transformation process required compared to first-g eneration biofuels, the main advantages of lignocellulosic crops used to produce advanced ethanol are the lower environmental impacts during cultivation (Adler, Del Grosso, & Parton, 2007; Fazio & Monti, 2011), the possibility to reduce biogenic greenhouse gases (GHG) emissions through soil organic carbon (SOC) storage (Agostini, Gregory, & Richter, 2015) and the opportunity to avoid competition for land, since they can satisfactorily grow in marginal situations (Quinn et al, 2015) that would not be suited for the cultivation of conventional food crops
While conversion of existing croplands to biofuel feedstock crops will often increase SOC in those systems (Davis et al, 2012; Qin, Dunn, Kwon, Mueller, & Wander, 2016), the displacement of existing crop production can lead to an indirect land use change (ILUC) effect due to the conversion of more land somewhere else as an answer to increased prices (Searchinger et al, 2008)
As previously for switchgrass (Nocentini et al, 2015), giant reed growth was divided in phases, since a decline in yields in time has been observed in our field experiments (Monti & Zegada-Lizarazu, 2015), and in the literature (Angelini, Ceccarini, Nassi o Di Nasso, & Bonari, 2009), both showing the decline to occur after the eighth year after establishment
Summary
In order to achieve energy security (uninterrupted availability of energy sources at an affordable price) and a reduction in greenhouse gases (GHG) emissions (sustainability), policies have been promulgated in the United States for the production of bioenergy from lignocellulosic feedstocks, including the Renewable Fuel Standard. On the contrary, converting marginal croplands may generate ILUC effects, but will likely generate great GHG benefits through SOC deposition (Qin et al, 2016)
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