Impacts of Land Conversion for Biofuel Cropping on Soil Organic Matter and Greenhouse Gas Emissions

To assess the value of biofuels, the environmental costs of their production must be compared with the benefits of displacing fossil fuel. This article focuses on the environmental impacts of biofuel cropping systems and calculates net greenhouse gas (GHG) emissions using life cycle analysis. The impacts of corn and switchgrass cropping for ethanol production were calculated for three states in the US (Iowa, Illinois, and Indiana) assuming three previous land use scenarios: Conservation Reserve Program (CRP) land, pasture land, and land already used for cropping. Although the results were different for the 3 states considered, the impacts of previous land use and cropping system were more important than location. Conversion of CRP lands to corn ethanol production would result in little net GHG savings compared to burning fossil fuel, greatly increase NO3 leaching, and constrain other benefits of CRP land such as wildlife habitat. Conversion of pasture and crop land to corn ethanol cropping show GHG benefits, reductions in leaching for previously cropped systems, and increases in leaching for lands previously in pasture. Converting CRP land to switchgrass cropping would lessen the rate at which these soils store SOC, increase N2O emissions, and have little impact on NO3 leaching. Converting pasture and crop land to switchgrass cropping would increase SOC storage, decrease N2O emissions, and decrease NO3 leaching. We conclude that current land management (cropping system, tillage intensity, and fertilizer application), as well as previous land use, must both be considered to quantify the environmental impacts of biofuel cropping systems.