Adler, Paul (USDA-ARS, Building 3702, Curtin Road, University Park, PA, 16802-3702; Phone: 814-865-8894; Fax: 814-863-0935; Email: paul.adler@ars.usda.gov)

Climate Change Effects on Greenhouse Gas Emissions From Bioenergy Cropping Systems in Pennsylvania

P.R. Adler*, S.J. Del Grosso, W.J. Parton

Reducing the net global warming potential (GWP) of energy use is a major factor driving interest in biofuels. Bioenergy cropping systems vary in contribution to the GWP due to the crop yield and resulting quantity of fossil fuels displaced, quantity and quality of C added to the soil, feedstock conversion efficiency, N₂O emissions, N use efficiency, and inputs required for crop production and operation of farm machinery. The objective of the study was to use DAYCENT to model the impact of climate change on net greenhouse gas (GHG) emissions of bioenergy cropping systems (corn, soybeans, alfalfa, switchgrass, reed canarygrass, and hybrid poplar) in Pennsylvania for inclusion in a full C cycle analysis. Weather data driving climate change scenarios were from VEMAP for the no change in climate scenario and from the Canadian Centre for Climate Modeling and Analysis (CGCM1model) and Hadley Centre for Climate Prediction and Research, UK (HADCM2 model) for the climate change simulations where CO₂ was assumed to double from 2004 - 2100. Without additional N, there was little response of nonleguminous crops to climate change. Alfalfa yields nearly doubled without additional N, whereas the yields of soybean were mixed depending on climate model. When the rate of N application increased 4% per year in the climate change simulations, corn, reed canarygrass, and switchgrass yields increased. Although N loss through N₂O emissions and NO₃-N leaching also increased with N application, further optimization will minimize these loses. Reed canarygrass had the highest N₂O emissions and NO₃-N leaching followed by corn and switchgrass and then soybeans and alfalfa. The greatest increase in soil C levels occurred with switchgrass, followed by corn, soybean and reed canarygrass were about neutral, and during the alfalfa segment in the corn soybean alfalfa crop rotation, soil C decreased. The quantity of displaced fossil fuel was the largest GHG sink. Soil C sequestration was the second largest GHG sink. Although crops with higher soil C inputs, such as switchgrass and hybrid poplar, will have higher equilibrium soil C levels, the change in system C will approach zero in the long term. N₂O emissions were the largest GHG source. When the credit for the amount of fossil fuel displaced was not taken into account and soil C storage was assumed to have reached its maximum capacity, switchgrass and hybrid poplar were the only cropping systems to remain a sink for GHGs. Therefore, use of switchgrass and hybrid poplar for production of biofuels has the potential to be GHG neutral and may even be a long-term sink for GHGs.