Publication Date:
2011-10-28
Description:
It is important to demonstrate that replacing fossil fuel with bioenergy crops can reduce the national greenhouse gas (GHG) footprint. We compared field emissions of nitrous oxide (N 2 O), methane (CH 4 ) and soil respiration rates from the C 4 grass Miscanthus × giganteus and willow ( salix) with emissions from annual arable crops grown for food production. The study was carried out in NE England on adjacent fields of willow , Miscanthus , wheat ( Triticum aetivum ) and oilseed rape ( Brassica napus ). N 2 O, CH 4 fluxes and soil respiration rates were measured monthly using static chambers from June 2008 to November 2010. Net ecosystem exchange (NEE) of carbon dioxide (CO 2 ) was measured by eddy covariance on Miscanthus from May 2008 and on willow from October 2009 until November 2010. The N 2 O fluxes were significantly smaller from the bioenergy crops than that of the annual crops. Average fluxes were 8 and 32 μg m −2 h −1 N 2 O-N from wheat and oilseed rape, and 4 and 0.2 μg m −2 h −1 N 2 O-N from Miscanthus and willow, respectively. Soil CH 4 fluxes were negligible for all crops and soil respiration rates were similar for all crops. NEE of CO 2 was larger for Miscanthus (−770 g C m −2 h −1 ) than willow (−602 g C m −2 h −1 ) in the growing season of 2010. N 2 O emissions from Miscanthus and willow were lower than for the wheat and oilseed rape which is most likely a result of regular fertilizer application and tillage in the annual arable cropping systems. Application of 15 N-labelled fertilizer to Miscanthus and oil seed rape resulted in a fertilizer-induced increase in N 2 O emission in both crops. Denitrification rates (N 2 O + N 2 ) were similar for soil under Miscanthus and oilseed rape. Thus, perennial bioenergy crops only emit less GHGs than annual crops when they receive no or very low rates of N fertilizer.
Print ISSN:
1757-1693
Electronic ISSN:
1757-1707
Topics:
Energy, Environment Protection, Nuclear Power Engineering
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