Comparison of soil greenhouse gas fluxes from extensive and intensive grazing in a temperate maritime climate

Abstract

Greenhouse gas (GHG) fluxes from a seminatural, extensively sheep-grazed drained moorland and intensively sheep-grazed fertilised grassland in South East (SE) Scotland were compared over 4 yr (2007–2010). Nitrous oxide (N₂O) and methane (CH₄) fluxes were measured by static chambers, respiration from soil plus ground vegetation by a flow-through chamber, and the net ecosystem exchange (NEE) of carbon dioxide (CO₂) by eddy-covariance. All GHG fluxes displayed high temporal and interannual variability. Temperature, radiation, water table height and precipitation could explain a significant percentage of seasonal and interannual variations. Greenhouse gas fluxes were dominated by the net ecosystem exchange of CO₂ at both sites. Net ecosystem exchange of CO₂ and respiration was much larger on the productive fertilised grassland (−1567 and 7157 g CO₂_eq m⁻² yr⁻¹, respectively) than on the seminatural moorland (−267 and 2554 g CO₂_eq m⁻² yr⁻¹, respectively). Large ruminant CH₄ (147 g CO₂_eq m⁻² yr⁻¹) and soil N₂O (384 g CO₂_eq m⁻² yr^−1) losses from the grazed grassland counteracted the CO₂ uptake by 34%, whereas the small N₂O (0.8 g CO₂_eq m⁻² yr^−1) and CH₄ (7 g CO₂_eq m⁻² yr⁻¹) emissions from the moorland only impacted the NEE flux by 3%. The 4-yr average GHG budget for the grazed grassland was −1034 g CO₂_eq m⁻² yr⁻¹ and −260 g CO₂_eq m⁻² yr⁻¹ for the moorland.