The Energy Independence and Security Act of 2007established national targets for the production of renewable transportation fuels in the U.S. These targets are presently being met through the production of corn grain ethanol. Advanced biofuels derived from lignocellulosic materials, however, are expected to comprise a growing proportion of the renewable energy portfolio and provide a more sustainable solution in the long term. To improve understanding of potential ecological and economic tradeoffs associated with growing lignocellulosic materials for bioenergy production, in 2008 we established a replicated field experiment in central Iowa, USA, which includes five biomass cropping systems grown across a toposequence of five landscape positions. In this experiment, called the Landscape Biomass Project, we are assessing above-ground biomass yield, below-ground carbon pools, greenhouse-gas emissions, soil moisture levels, water quality, and management costs and benefits for each cropping system grown at each landscape position.
Results/Conclusions
Baseline work has established the impacts of a 50 year cropping history on soil parameters, including the capacity of soils located across the toposequence to store carbon; the summit and shoulder positions pose the highest potential and the floodplain the lowest. The continuous corn system has consistently produced among the highest above-ground biomass yields. The triticale-sorghum system, however, which yields two biomass crops per year, matched corn yields in four of five landscape positions and outperformed corn at the backslope position during 2010, a wet year. Nitrate-nitrogen concentrations in soil water are significantly lower in this cropping system in comparison to continuous corn, as is case for the switchgrass system. Soil moisture levels are lower in the short-rotation woody biomass crop system, which may be due to higher levels of evapotranspiration associated with the tree crop. The fuller understanding of the ecological parameters of biomass cropping systems such as these will help inform regional models that strive to predict the impacts of agricultural land-use change and governmental policies that seek to incentivize the development of a more sustainable bioenergy industry.