Abstract
Abstract. The production of bioenergy in Europe is one of the strategies conceived to reduce greenhouse gas (GHG) emissions. The suitability of the land use change from a cropland (REF site) to a short-rotation coppice plantation of hybrid poplar (SRC site) was investigated by comparing the GHG budgets of these two systems over 24 months in Viterbo, Italy. This period corresponded to a single rotation of the SRC site. The REF site was a crop rotation between grassland and winter wheat, i.e. the same management of the SRC site before the conversion to short-rotation coppice. Eddy covariance measurements were carried out to quantify the net ecosystem exchange of CO2 (FCO2), whereas chambers were used to measure N2O and CH4 emissions from soil. The measurements began 2 years after the conversion of arable land to SRC so that an older poplar plantation was used to estimate the soil organic carbon (SOC) loss due to SRC establishment and to estimate SOC recovery over time. Emissions from tractors and from production and transport of agricultural inputs (FMAN) were modelled. A GHG emission offset, due to the substitution of natural gas with SRC biomass, was credited to the GHG budget of the SRC site. Emissions generated by the use of biomass (FEXP) were also considered. Suitability was finally assessed by comparing the GHG budgets of the two sites. CO2 uptake was 3512 ± 224 g CO2 m−2 at the SRC site in 2 years, and 1838 ± 107 g CO2 m−2 at the REF site. FEXP was equal to 1858 ± 240 g CO2 m−2 at the REF site, thus basically compensating for FCO2, while it was 1118 ± 521 g CO2 m−2 at the SRC site. The SRC site could offset 379.7 ± 175.1 g CO2eq m−2 from fossil fuel displacement. Soil CH4 and N2O fluxes were negligible. FMAN made up 2 and 4 % in the GHG budgets of SRC and REF sites respectively, while the SOC loss was 455 ± 524 g CO2 m−2 in 2 years. Overall, the REF site was close to neutrality from a GHG perspective (156 ± 264 g CO2eq m−2), while the SRC site was a net sink of 2202 ± 792 g CO2eq m−2. In conclusion the experiment led to a positive evaluation from a GHG viewpoint of the conversion of cropland to bioenergy SRC.
Highlights
In the current regulation concerning energy and climate change policies, the European Union (EU) established two targets for 2020: (i) a reduction of 20 % of greenhouse gas (GHG) emissions relative to the levels of 1990, and (ii) a share of 20 % renewable energy use in gross final energy consumption (European Commission, 2007, 2008)
from production and transport of agricultural inputs (FMAN) includes the GHG emissions related to the management of the Shortrotation coppices (SRC) site, and FSOC is the loss of soil organic carbon content due to the installation of the cuttings
The cumulative FCO2 at the REF site for the 2 years considered was −1838 ± 107 g CO2 m−2, partitioned into 8032 ± 313 g CO2 m−2 absorbed through photosynthesis (GPP) and 6216 ± 338 g CO2 m−2 emitted by total Reco
Summary
In the current regulation concerning energy and climate change policies, the European Union (EU) established two targets for 2020: (i) a reduction of 20 % of greenhouse gas (GHG) emissions relative to the levels of 1990, and (ii) a share of 20 % renewable energy use in gross final energy consumption (European Commission, 2007, 2008). In recent years researchers have approached poplar SRCs from different perspectives: ecological (Jaoudé et al, 2011; Zhou et al, 2013), economic (Strauss and Grado, 1997; Mitchell et al, 1999; El Kasmioui and Ceulemans, 2012, 2013), and related to energy production and different environmental aspects (Jungmeier and Spitzer, 2001; Cherubini et al, 2009; Davis et al, 2009; Nassi o Di Nasso et al, 2010; Arevalo et al, 2011; Don et al, 2012; Dillen et al, 2013; Djomo et al, 2013). Given that the climate change mitigation potential of energy crops is the main reason for subsidies to arable land conversion, our study aimed to assess the suitability of the LUC to SRC in terms of the mitigation of GHG emissions
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