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Key findings

  • Soil N2O emissions were seen to be small relative to CO2 emissions from the soil, and CH4 emissions were negligible across all transitions to 2G bioenergy crops (Miscanthus, SRC-W and SRF)
  • Changes in soil carbon stocks were the primary determinant of whether a given transition to bioenergy crops was beneficial or negative in terms of a site’s net soil GHG emissions, modelled over 40 years
  • Transitions from arable land to 2G bioenergy crops showed net GHG savings (increase in soil carbon and/or reduction in GHG fluxes), relative to continued arable land use. These savings were predominantly seen as gains in soil carbon in the top 0-30cm layer, likely to be due to some combination of: a) less disturbance of soil through tillage / harrowing) less fertiliser inputs (resulting in reduced N2O emissions and negligible CH4 emissions); and c) less microbial driven losses of soil carbon, so more carbon retained in soil
  • Across the UK, all assessed transitions from arable to 2G bioenergy crops delivered GHG savings (mean net soil GHG emissions over 40 years were -84, -42 and -144 tCO2e ha-1 for Miscanthus, SRC-W and SRF respectively). with arable to high-yielding Short rotation forestry (SRF)  transitions offering the greatest GHG savings potential for this part of the value chain. 
  • Soil carbon losses were higher in soils initially rich in soil organic carbon at Miscanthus and SRC-W sites
  • The establishment of SRF on UK agricultural land is likely to result in either no change in soil C, or a small increase, depending on the tree species planted. Coniferous SRF species such as Sitka Spruce were seen to have an increase in soil carbon at both 0-30cm and 0-100cm depths relative to control sites, whereas broadleaf SRF species tended to see no change in soil carbon levels (i.e. a neutral transition)
  • Transitions from grassland to first generation (1G) crops: wheat, oilseed rape and sugar beet, showed significantly greater net increases in soil GHG emissions than grassland to 2G bioenergy crops.
  • Transitions from forest to any other crop generally resulted in increased soil GHG emissions, as a result of reductions in soil carbon and increased CO2 fluxes. Net GHG emissions of 107, 134 and 92 tCO2e ha-1 after 40 years were predicted for Miscanthus, SRC and SRF respectively, compared to leaving it as mature forest
  • Modelling outputs showed the spatial distribution of locations likely to deliver net soil GHG savings varied by transition type. Favourable locations for arable to 2G bioenergy crop transitions were relatively uniformly spread across the UK; whilst locations for grassland to SRF transitions for example, were concentrated in the central to southern parts of the UK
  • Yield had a larger impact on modelled net soil GHG emissions than small variations in fertiliser input (+/- 20% around Defra guideline amounts), or climate scenario predictions (UKCP0920), with higher yields resulting in lower emission levels over 40 years

Publications are available here

This project was commissioned and funded by the Energy Technologies Institute

energy technologies institute

The ELUM Consortium is led by the Centre for Ecology & Hydrology (CEH) and includes the following organisations:

  • Centre for Ecology & Hydrology
  • University of Aberdeen
  • University of Southampton
  • Forest Research
  • Aberystwith University
  • University of Edinburgh
  • The University of York