Nitrogen cycle impacts of short-rotation woody crop establishment across the Northern Lake States

Background/Question/Methods

Short-rotation woody biofuels crops (SRWC) are expected to become one of the major feedstocks for bioenergy generation in the Midwest region.  The federal mandate for 36 billion gallons of biofuels by 2022, combined with incentives for biomass-fired power plants, has accelerated development of alternative feedstock sources, including SRWC, with proposed plantations on large acreages of non-forested land in the Northern Lake States.  However, the environmental impacts of widespread land conversion remain uncertain.  In our study, we investigated the effects of establishing willow and hybrid-poplar plantations on soil N cycling, N₂O emissions, and NO₃^- leaching at six sites of varying soil and climate conditions across northern Michigan and Wisconsin.

Results/Conclusions

All six sites responded to establishment with increased N₂O emissions, available inorganic N, and NO₃^- leaching; however, the magnitude of these impacts was strongly controlled by underlying site conditions.  We found the greatest impacts on organic-matter (OM) rich, lacustrine soils and the smallest impacts on OM-poor, outwash sands.  The range of N₂O emissions in the first growing season was nearly 30-fold, from 0.34 to 10.0 Mg-CO₂eq ha^-1.  Nitrate production in soil varied 3-fold among sites, with peak extractable NO₃^- concentrations ranging from 15 to 48 g N kg soil-1.  These results demonstrate that the N-cycle impacts of SRWC establishment vary predictably with underlying site conditions; thus understanding the landscape- and regional-scale impacts of a developing regional SRWC industry will need to account for the complex geomorphology of open lands across the northern Lake States.