Landscape Control of Nitrous Oxide Emission in Biomass Crops in the Ridge and Valley Ecoregion.

The widespread adoption of biomass crops for energy purposes depends on the capacity of production systems to deliver large amounts of biomass with relatively low inputs and environmental impacts. In the Ridge and Valley ecoregion of Pennsylvania, the topography and soils favor water accumulation around seeps and lower landscape positions in soils seemingly suitable for switchgrass and miscanthus based biomass production.  While these crops can use residual nutrients from upland annual cropping, there is also a risk that the excessive wetness increases denitrification induced nitrous oxide (N₂O) fluxes. With the goal of quantifying N₂O fluxes in these systems, we established a set of plot and landscape experiments near the town of Leck Kill, PA.  Switchgrass and miscanthus are being grown with different management strategies at diverse landscape positions using Conservation Reserve Program as a control.  Soil water is being continuously monitored using a network of 144 soil moisture sensors distributed in a 5-ha watershed. Fluxes of N₂O will be monitored using the static steady state gas chamber method along with water quality in regular monthly samplings and after strong rain storms or snow melting events. Preliminary modeling exercises (no landscape component) with the model Cycles indicate that in unfertilized switchgrass, N₂O emissions and nitrate leaching are low (<0.2 and < 6 kg N ha^-1 yr^-1, respectively), yet with 100 kg of N added as fertilizer in April these losses increase on average to 1.5 and 56 kg N ha^-1 yr^-1, respectively. Interestingly, in the no fertilizer simulation the (low) N₂O emissions were higher during the middle of the summer (nitrification), while when fertilized losses were higher after the fertilization event and in fall, but highly erratic. These results warrant further studies of the landscape control of N losses and N management to optimize production and environmental goals.