Cradle to farm gate lifecycle inventory and water quality impacts associated with nutrients used for corn, soy, and stover biomass feedstocks

The production of corn or soybeans for bio-based fuels and materials requires significant inputs of nitrogen (FN) and phosphorus fertilizer (FP) to increase grain yields. Approximately 50% of these nutrients are integrated into plant biomass. The remaining 50% is volatilized, leached into surface and groundwater, or transformed into gaseous species such as N2, NO, or N2O. Recent efforts to complete lifecycle inventories for bio-products based on corn, soy or corn stover feedstocks have largely ignored flows of fertilizer nitrogen and phosphorus to surface water bodies. The studies that have included nutrient leaching generally assume that a constant fraction of the fertilizer is leached, typically ~24-30%. This approach fails to integrate the very wide variability in leaching rates and, therefore, fails to adequately predict yearly variability in eutrophication and hypoxia.