Comparison of GHG emissions from annual crops in rotation on drained temperate agricultural peatland with production of reed canary grass in paludiculture using an LCA approach.

Drained peat soils contribute significantly to global human-caused CO emissions and reducing peat degradation via rewetting is high on the political agenda. Ceasing agricultural activities on rewetted soils might lead to land owner resistance and high societal expenses to compensate farmers. Continued biomass production adapted for wet conditions on peat soils potentially minimizes these costs and helps supplying the growing demand for e.g. materials, fuels and feed. Here we used a life cycle assessment approach (cradle to farm gate) to investigate the greenhouse gas (GHG) emissions related to three cases by applying IPCC (Intergovernmental Panel on Climate Change) emission factors and specific site conditions at a bog and a fen site that represent widely distributed temperate peat soils. Besides soil emissions, upstream emissions from input, operational emissions and emission related to rewetting construction work were included. The analyzed systems were deeply drained cash cropping on agricultural bog (potatoes ( L.), spring barley ( L.) and oat ( L.), permanent Reed canary grass (RCG) ( L.) production on non-drained bog and permanent RCG production on shallow-drained fen. The annual mean water table depths (WTD) were -70, -38 (estimated) and -13 cm, respectively. Results showed estimated GHG emissions of 40.5, 26.1 and 20.6 Mg COeq ha, respectively, corresponding to a 35% GHG reduction for the non-drained bog case as compared to the drained bog case, despite that the obtained WTD due to ceased drainage did not adhere to the IPCC rewetting threshold of -30 cm. Emissions related to crop management represented 7, 14 and 19% of total emissions. In the RCG cultivation on fen case, the WTD were controlled primarily by the water table of the nearby stream and total GHG emissions were even lower as compared to the RCG production on the non-drained bog reflecting the difference in WTD. Rewetting projects need to include careful knowledge of the specific peat area to foresee the actual reduction potential.