Greenhouse gas balance of cropland conversion to bioenergy poplar short-rotation coppice

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 CO 2 (F CO 2 ), whereas chambers were used to measure N 2 O and CH 4 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 (F MAN ) 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 (F EXP ) were also considered. Suitability was finally assessed by comparing the GHG budgets of the two sites. CO 2 uptake was 3512 ± 224 g CO 2 m −2 at the SRC site in 2 years, and 1838 ± 107 g CO 2 m −2 at the REF site. F EXP was equal to 1858 ± 240 g CO 2 m −2 at the REF site, thus basically compensating for F CO 2 , while it was 1118 ± 521 g CO 2 m −2 at the SRC site. The SRC site could offset 379.7 ± 175.1 g CO 2 eq m −2 from fossil fuel displacement. Soil CH 4 and N 2 O fluxes were negligible. F MAN made up 2 and 4 % in the GHG budgets of SRC and REF sites respectively, while the SOC loss was 455 ± 524 g CO 2 m −2 in 2 years. Overall, the REF site was close to neutrality from a GHG perspective (156 ± 264 g CO 2 eq m −2 ), while the SRC site was a net sink of 2202 ± 792 g CO 2 eq m −2 . In conclusion the experiment led to a positive evaluation from a GHG viewpoint of the conversion of cropland to bioenergy SRC.

P-model v1.0: an optimality-based light use efficiency model for simulating ecosystem gross primary production

“…f gravel is the gravel fraction, z bedrock is the depth to bedrock (in mm), and z max is 2000 mm. The volumetric soil water storage at field capacity and wilting point were derived from texture and organic matter content data through pedotransfer functions, as described by Saxton and Rawls (2006). W FC is calculated as…”

Greenhouse gas budget of a poplar bioenergy plantation in Belgium: CO2 uptake outweighs CH4 and N2O emissions

“…Also, because of the absence of annual soil tillage under SRC as in the case of annual crops, the CO 2 emissions due to soil disturbance are minimized. The heavy machinery used during harvest may also lead to soil compaction with less aeration and water infiltration affecting the biological processes and related GHG effluxes from the soil (Epron et al, 2016;Sabbatini et al, 2016). The effect of a larger rooting system could cancel out this effect, depending on the poplar genotype (Berhongaray, Janssens, King, & Ceulemans, 2013) and the soil.…”

Eddy covariance flux errors due to random and systematic timing errors during data acquisition

“…The fundamental difference between time lags on one side and RTE/STE on the other side is that constant time lags can, at least in principle, be addressed a posteriori during data processing. The topic of correctly estimating and compensating time lags has long been discussed in the EC literature (Vickers and Mahrt, 1997;Ibrom et al, 2007;Massman and Ibrom, 2008;Langford et al, 2015), and corresponding algorithms are available in EC processing software. We will therefore not further discuss time lags in this paper.…”

“…Before calculating covariances, standard EC processing steps were applied such as spike removal (Vickers and Mahrt, 1997), tilt correction by the double rotation method (Wilczak et al, 2001), and fluctuation estimation via block-averaging. Covariance estimates obtained with the new versions of T s were then compared with the reference to quantify the effect of simulated timing errors.…”

“…The EC tower was installed at the end of 2011, and measurements were taken until mid-2015. The period used for the simulation included 9 months over the period 2012-2015, with a canopy height ranging 0-5.3 m, and the measurement height between 3 and 5.5 m (Sabbatini et al, 2016).…”