Influence of organic ley–arable management and afforestation in sandy loam to clay loam soils on fluxes of N2O and CH4 in Scotland

Assessment of the sustainability of alternatives to conventional uses of agricultural land, viz. organic systems and afforestation should include consideration of any effects on trace gas budgets. Nitrous oxide (N₂O) and methane (CH₄) fluxes and controlling soil properties were measured in an organic ley–arable rotation in north-east Scotland on a sandy loam. N₂O fluxes were monitored in the ley and arable phases and in organic permanent grass (Lolium perenne) located nearby throughout the 3-year phase duration. Gas fluxes in woodland that had been converted from arable for 1 or 6 years were also measured in both north-east and south-east Scotland on sandy loam to clay loam soils. The climate is maritime and variable with annual rainfall between 800 and 900 mm. Within the organic rotation, differences in N₂O fluxes between the ley and arable phases were less marked than in conventional agriculture. Although this was mainly because grassland emissions were low, some losses from the arable component were also relatively high. Seasonal rainfall had a major influence on cumulative emissions of N₂O, including the first year after conversion from ley to arable. In the short term, changing land use from arable to woodland increased CH₄ oxidation rates and decreased N₂O emissions, though both these rates were also influenced by seasonal weather. Afforestation of agricultural land appears to be more beneficial to trace gas exchange than conversion to organic production.