A Miscanthus plantation can be carbon neutral without increasing soil carbon stocks

Andy D. Robertson*, Jeanette Whitaker, Ross Morrison, Christian A. Davies, Pete Smith, Niall P. Mcnamara

*Corresponding author for this work

Research output: Contribution to journalArticle

15 Citations (Scopus)
12 Downloads (Pure)

Abstract

National governments and international organizations perceive bioenergy, from crops such as Miscanthus, to have an important role in mitigating greenhouse gas (GHG) emissions and combating climate change. In this research, we address three objectives aimed at reducing uncertainty regarding the climate change mitigation potential of commercial Miscanthus plantations in the United Kingdom: (i) to examine soil temperature and moisture as potential drivers of soil GHG emissions through four years of parallel measurements, (ii) to quantify carbon (C) dynamics associated with soil sequestration using regular measurements of topsoil (0-30 cm) C and the surface litter layer and (iii) to calculate a life cycle GHG budget using site-specific measurements, enabling the GHG intensity of Miscanthus used for electricity generation to be compared against coal and natural gas. Our results show that methane (CH4) and nitrous oxide (N2O) emissions contributed little to the overall GHG budget of Miscanthus, while soil respiration offset 30% of the crop's net aboveground C uptake. Temperature sensitivity of soil respiration was highest during crop growth and lowest during winter months. We observed no significant change in topsoil C or nitrogen stocks following 7 years of Miscanthus cultivation. The depth of litter did, however, increase significantly, stabilizing at approximately 7 tonnes dry biomass per hectare after 6 years. The cradle-to-farm gate GHG budget of this crop indicated a net removal of 24.5 t CO2-eq ha-1 yr-1 from the atmosphere despite no detectable C sequestration in soils. When scaled up to consider the full life cycle, Miscanthus fared very well in comparison with coal and natural gas, suggesting considerable CO2 offsetting per kWh generated. Although the comparison does not account for the land area requirements of the energy generated, Miscanthus used for electricity generation can make a significant contribution to climate change mitigation even when combusted in conventional steam turbine power plants.

Original languageEnglish
Pages (from-to)645-661
Number of pages17
JournalGlobal Change Biology. Bioenergy
Volume9
Issue number3
Early online date9 Nov 2016
DOIs
Publication statusPublished - Mar 2017

Keywords

  • Bioenergy
  • Coal
  • Decomposition
  • Greenhouse gas
  • Greenhouse gas intensity
  • Life cycle assessment
  • Litter
  • Natural gas
  • Net ecosystem exchange
  • Soil C

ASJC Scopus subject areas

  • Forestry
  • Renewable Energy, Sustainability and the Environment
  • Agronomy and Crop Science
  • Waste Management and Disposal

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