Spatial and Temporal Variation in N2O Emissions from Perennial Bioenergy Production on Marginal Soils.

Nitrous oxide is the 3^rd most important anthropogenic greenhouse gas, and is the single most significant ozone destroying gas emitted to the atmosphere. More than three fourths of all N₂O emissions in the U.S. are due to nitrogen fertilization and cropping practices in agriculture. Poorly drained marginal soils are often considered to be major sources of N₂O due to their persistent high moisture content which favors denitrification. Poorly drained marginal soils are not often suited for traditional row cropping and tillage agriculture. We explored the potential of two perennial grasses, switchgrass (Panicum virgatum) and miscanthus (Miscanthus giganteus), to produce perennial bioenergy feedstock and to mitigate N₂O emissions on marginal soils in the Upper Chesapeake Bay watershed. Five feedstock and fertilizer combinations were compared to a native cool season grass mix to determine best management practices for marginal soils in the ridge and valley province. We found the highest rates of N₂O emissions arose from switchgrass fertilized with 50 kg ha^-1 of NH₄SO₄ followed by switchgrass fertilized with the equivalent broiler manure. Emissions from unfertilized switchgrass and miscanthus were similar to N₂O emissions from a mix of cool season natives and switchgrass grown alongside the legume showy tick trefoil (Desmodium canadense). Nitrous oxide emissions generally peaked with the first significant rainfall event following fertilization and were spatially heterogeneous. High levels of N₂O emissions were found when water filled pore space was > 50%, soil solution NO₃^- was > 6ppm and soil O₂ concentrations were relatively high indicating that N₂O emissions were coming from both nitrification and denitrification.