Recent LCA Studies Illustrate the Need for Improved Information on Impacts Associated with Changes in Belowground and Soil Carbon in Willow Biomass Crops

Empirical data is lacking on belowground stored carbon and changes in soil carbon over time in willow biomass systems, especially when this involves a transition from different land uses into willow. Recent life cycle assessment (LCA) studies have shown the importance of these factors on the life cycle greenhouse gas emissions of willow biomass crops. A spatial LCA model in Central and Northern New York indicates that 92% of 9,718 suitable parcels for willow biomass production had negative GHG emissions. The average life cycle GHG emissions in the region were -126.8 kg CO₂eq Mg^-1 biomass on previous cropland or pasture land and ranged from -53.2 kg to -176.9 kg CO₂eq Mg^-1 across the region. However, for grassland converted to willow biomass crops, there was a modeled decrease in soil organic carbon (SOC) resulting in a slightly positive (27.7 kg CO₂eq Mg^-1 biomass) GHG balance. Uncertainty analysis showed large variations of probability distributions of GHG emissions in the five counties arising from differences in land use change, willow crop yield, and transportation distance. A LCA of willow biomass being converted to ethanol using hot water extraction and biological conversion also showed that belowground carbon storage and prior land use influenced on whether these systems had negative or positive emissions. Improved data on soil carbon dynamics and the belowground portion of willow biomass crops is needed to resolve this uncertainty.