Abstract
AbstractFor avoiding competition with food production, marginal land is economically and environmentally highly attractive for biomass production with short‐rotation coppices (SRCs) of fast‐growing tree species such as poplars. Herein, we evaluated the environmental impacts of technological, agronomic, and environmental aspects of bioenergy production from hybrid poplar SRC cultivation on marginal land in southern Germany. For this purpose, different management regimes were considered within a 21‐year lifetime (combining measurements and modeling approaches) by means of a holistic Life Cycle Assessment (LCA). We analyzed two coppicing rotation lengths (7 × 3 and 3 × 7 years) and seven nitrogen fertilization rates and included all processes starting from site preparation, planting and coppicing, wood chipping, and heat production up to final stump removal. The 7‐year rotation cycles clearly resulted in higher biomass yields and reduced environmental impacts such as nitrate (NO3) leaching and soil nitrous oxide (N2O) emissions. Fertilization rates were positively related to enhanced biomass accumulation, but these benefits did not counterbalance the negative impacts on the environment due to increased nitrate leaching and N2O emissions. Greenhouse gas (GHG) emissions associated with the heat production from poplar SRC on marginal land ranged between 8 and 46 kg CO2‐eq. GJ−1 (or 11–57 Mg CO2‐eq. ha−1). However, if the produced wood chips substitute oil heating, up to 123 Mg CO2‐eq. ha−1 can be saved, if produced in a 7‐year rotation without fertilization. Dissecting the entire bioenergy production chain, our study shows that environmental impacts occurred mainly during combustion and storage of wood chips, while technological aspects of establishment, harvesting, and transportation played a negligible role.
Highlights
Anthropogenic greenhouse gas (GHG) emissions need to decrease substantially in order to limit the global temperature rise to 2 °C compared to the pre-industrial period (UNFCCC, 2015) and to avoid that the global biosphere crosses irreversible tipping points (e.g., Ramanathan & Feng, 2008)
The application of fertilizer after each harvest had no significant influence on the total aboveground biomass (AGB) of the poplar short-rotation coppices (SRCs); it lead to increased soil N2O emissions and stimulated nitrate leaching, especially in the 3-year rotation cycles (Fig. 3)
Our study shows that the Global Warming Potentials (GWPs) of the different production chains depended mostly on the length of the rotation cycles and successively on fertilization regimes, as indicated by the first and second principal components of the principal component analysis (PCA), respectively (Fig. 4)
Summary
Anthropogenic greenhouse gas (GHG) emissions need to decrease substantially in order to limit the global temperature rise to 2 °C compared to the pre-industrial period (UNFCCC, 2015) and to avoid that the global biosphere crosses irreversible tipping points (e.g., Ramanathan & Feng, 2008) In this context, the role of bioenergy production as a useful means to decrease GHG emissions from energy production is widely. A promising option to increase lignocellulosic biomass production for energy use is the use of short-rotation coppices (SRCs) of fast-growing tree species Such systems are considered as the most energy efficient carbon (C) conversion technology (Styles & Jones, 2007), which – if used for energetic purposes – can reduce the total GHG emissions by up to 90% compared to coal combustion (Djomo et al, 2010). Established as SRC on marginal agricultural sites, they further have the potential to increase soil C sequestration (Anderson-Teixeira et al, 2013), while reducing soil nitrate (Dıaz-Pines et al, 2016)
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