Sustainable bioenergy production from marginal lands in the US Midwest

A comparative assessment of six alternative cropping systems over 20 years shows that, once well established, successional herbaceous vegetation grown on marginal lands has a direct greenhouse gas emissions mitigation capacity that rivals that of purpose-grown crops. Biofuel production at the margins Productive agricultural land that could otherwise be used to produce much-needed food crops is being diverted towards grain-based ethanol production in both Europe and the United States, partly in response to government legislation. An alternative is to grow cellulosic crops on so-called marginal lands. An evaluation of the potential of marginal lands in the Midwestern United States to produce biofuel while mitigating direct greenhouse gas emissions now finds that they have the capacity to produce a significant amount of biofuel energy without the initial carbon debt and indirect land-use costs associated with food-based biofuels. Legislation on biofuels production in the USA 1 and Europe 2 , 3 is directing food crops towards the production of grain-based ethanol 2 , 3 , which can have detrimental consequences for soil carbon sequestration 4 , nitrous oxide emissions 5 , nitrate pollution 6 , biodiversity 7 and human health 8 . An alternative is to grow lignocellulosic (cellulosic) crops on ‘marginal’ lands 9 . Cellulosic feedstocks can have positive environmental outcomes 10 , 11 and could make up a substantial proportion of future energy portfolios 12 , 13 . However, the availability of marginal lands for cellulosic feedstock production, and the resulting greenhouse gas (GHG) emissions, remains uncertain. Here we evaluate the potential for marginal lands in ten Midwestern US states to produce sizeable amounts of biomass and concurrently mitigate GHG emissions. In a comparative assessment of six alternative cropping systems over 20 years, we found that successional herbaceous vegetation, once well established, has a direct GHG emissions mitigation capacity that rivals that of purpose-grown crops (−851 ± 46 grams of CO 2 equivalent emissions per square metre per year (gCO 2 e m −2 yr −1 )). If fertilized, these communities have the capacity to produce about 63 ± 5 gigajoules of ethanol energy per hectare per year. By contrast, an adjacent, no-till corn–soybean–wheat rotation produces on average 41 ± 1 gigajoules of biofuel energy per hectare per year and has a net direct mitigation capacity of −397 ± 32 gCO 2 e m −2 yr −1 ; a continuous corn rotation would p