Carbon Sequestration and Gaseous Emissions in Perennial Grass Bioenergy Cropping Systems in the Northeastern US.

Conversion of marginal lands to perennial grass bioenergy crops is underway in the Northeast US, presenting both the challenge to define the long-term sustainability of these trends and the opportunity to observe the environmental impacts of land conversion from the outset. This project addresses sustainable bioenergy production by characterizing crops yields, trends and sequestration of soil carbon (C), and emissions of nitrous oxide (N₂O) and methane (CH₄). These impacts will be determined under current production practices on wetness-prone marginal soils for which very little relevant research exists despite being the primary available bioenergy land base in the region. Five years of testing is being carried out in replicated field-scale experiments.

We have established and are monitoring a large replicated field-scale perennial grass strip trial to determine effect of species, nitrogen (N) loading, and soil moisture status on yield, C sequestration and emissions. Due to wetness of the predominant Caneseraga-Dalton-Madalin soils, prior use of the 7 ha site (N42°28.20', W76° 25.94') was limited to occasional mowing or haying over the past 50 years. Quadruplicate ~0.4 ha strip plot treatments are switchgrass (Panicum virgatum v. Shawnee), switchgrass +N, reed canarygrass (Phalaris arundinaceae v. Bellevue)+N and non-converted control (fallow grassland). Permanent sampling points (5 per strip plot) were established along natural moisture gradients, representing 80 sampling points at which biomass yield and composition, soil characteristics and water content, rooting depth, soil C and root C mass are monitored. Given the variable nature of N₂O emissions, we are using an integrated approach to monitor trace gas emissions. Chamber campaigns will be used to compare N₂O and CH₄ emissions among treatments, while our continuous field-scale eddy-covariance system monitors the integrated field-scale response of N₂O at the primary site to allow tracking of area-wide responses to temperature or soil moisture shifts.

We are also conducting three less intensive field-scale trials on sites that represent a broader range of soils and landscape conditions. Sites include one new trial (mirroring the large-scale site layout) operated by cooperator Benetarra Agritech in Sherrill NY, and two mature switchgrass stands at Cornell University and at the State University of NY at Cobleskill. Finally, we will develop spatial tools to scale up our field results for perennial grass bioenergy crops on marginal soils, extending findings to multiscale assessments and decision tools.  Synthesis of yield, soil C and emissions with soil moisture status and modeled hydrologic characteristics will be carried out to link observed effects with site characteristics. We will then generalize the findings as a spatial hydrologic tool to better predict yield, C sequestration and emissions effects as a function of hydrologic and other relevant site characteristics.