Greenhouse Gas Emissions from Sustainable Intercropping of Switchgrass and Hybrid Poplar.

Major shifts in crop production will occur as farmers gear up to supply the demand for biomass feedstocks supporting biofuel production. These shifts will change agroecosystems services related to water use, carbon storage, nutrient cycling and greenhouse gas (GHG) emissions, that have direct consequences on air, water, and soil quality. Highly productive, commercial hybrid poplar (Populus generosa x P. canadensis) plantations are being successfully managed in the Pacific Northwest (PNW) for high-value timber production at relatively low stand densities (GreenWood Resources Inc.) under irrigation. The open understory created by low stocking rates was used for the production of cellulosic energy feedstocks; intercropped with switchgrass (Panicum virgatum) prior to canopy closure. In situ greenhouse gas fluxes were measured using the static closed chamber method according to the USDA-ARS GRACEnet protocols in plantings of hybrid poplar intercropped with cv Kanlow switchgrass over four years of production. Carbon storage over the last 4 years from switchgrass root biomass has shown a moderate increase ranging from 5 to 15% for switchgrass intercrop. Greenhouse gas and nitrous oxide fluxes increased following the application of nitrogen fertilizer. Nitrous oxide emissions increased annually as each crop increased in biomass and the amount of fertilizer and irrigation increased.