Short-rotation woody biomass crops (SRWC) have been proposed as a major feedstock source for bioenergy generation in the Northeastern US. To quantify the environmental effects and greenhouse gas (GHG) balance of crops including SRWC, investigators need spatially explicit data which encompass entire plantation cycles. A knowledge gap exists for the establishment period which makes current GHG calculations incomplete. In this study, we investigated the effects of converting pasture and hayfields to willow ( Salix spp.) and hybrid-poplar ( Populus spp.) SRWC plantations on soil nitrogen (N) cycling, nitrous oxide (N 2O) emissions, and nitrate (NO 3-) leaching at six sites of varying soil and climate conditions across northern Michigan and Wisconsin, following these plantations from pre conversion through their first 2 years. All six sites responded to establishment with increased N 2O emissions, available inorganic N, and, where it was measured, NO 3- leaching; however, the magnitude of these impacts varied dramatically among sites. Soil NO 3- levels varied threefold among sites, with peak extractable NO 3- concentrations ranging from 15 to 49 g N kg -1 soil. Leaching losses were significant and persisted through the second year, with 44-112 kg N ha -1 leached in SRWC plots. N 2O emissions in the first growing season varied 30-fold among sites, from 0.5 to 17.0 Mg-CO 2eq ha -1 (carbon dioxide equivalents). N 2O emissions over 2 years resulted in N 2O emissions due to plantation establishment that ranged from 0.60 to 22.14 Mg-CO 2eq ha -1 above baseline control levels across sites. The large N losses we document herein demonstrate the importance of including direct effects of land conversion in life-cycle analysis (LCA) studies of SRWC GHG balance. Our results also demonstrate the need for better estimation of spatial variability of N cycling processes to quantify the full environmental impacts of SRWC plantations.
