Use of Marginal Lands for Bioenergy Production

The definition of “marginal” with regard to productivity of arable lands varies greatly but in general marginal lands are those that have one or more characteristics not conducive to annual crop production.  Such characteristics as steep slopes, shallow soils, excessive wetness, or drought-proneness generally have negative effects on profitability of agricultural use and hence marginally lands usually are of fairly low value (i.e., comparatively low price per acre for rent or taxation purposes).  Remnants of native plant and animal communities persist on some marginal lands, in that they have never been plowed.  Row-crop production on some marginal lands is associated with high soil erosion ratesand decreased productivity over time as a result.  Marginal lands are typically used as pasture or for haying, but in times of high row crop prices, marginal lands are sometimes converted to row crops.  In the U.S., various public policies and federal programs such as the Conservation Reserve Program (CRP) have been created to slow or reverse such trends.  In addition to agricultural uses, marginal lands as a broad category of land type provide a variety of ecosystem services.  Policies and programs like CRP aim to protect the ecosystem services that marginal lands provide.

Marginal lands have recently been targeted for production of biomass for bioenergy, not only for meeting mandated renewable fuel mandates, but also as a potential means for avoiding land use conflicts contributing to a “food v. fuel” debate.  The 2007 U.S. Census of Agriculture identifies approximately 30 million acres of land including idle lands, land in cover crops for soil improvements, and fallow rotations as potentially available for biomass production including grasses and short-rotation woody species.  Conversion of steep or wet land currently in food crop production (i.e., row crop) to less intensive bioenergy crops such as high-diversity, low-input perennial mixes has the potential to generate more ecosystem services.  However, some researchers caution that conversion of marginal lands to more intensively managed bioenergy cropping systems could lead to permanent land degradation and net increase in GHGs.  Government, academic and private sector research is needed to assess whether and to what degree marginal lands can and should be relied upon for meeting future bioenergy demand.