Soil environmental variables affecting the flux of methane from a range of forest, moorland and agricultural soils

Measurements of the net methane exchange over a range of forest, moorland, and agricultural soils in Scotland were made during the period April to June 1994 and 1995. Fluxes of CH4 ranged from oxidation -12.3 to an emission of 6.8 ng m(-2) s(-1). The balance between CH4 oxidation and emission depended on the physical conditions of the soil, primarily soil moisture. The largest oxidation rates were found in the mineral forest soils, and CH4 emission was observed in several peat soils. The smallest oxidation rate was observed in an agricultural soil. The relationship between CH4 flux and soil moisture observed in pears (Flux(CH4) = 0.023 x %H2O (dry weight) - 7.44, p < 0.05) was such that CH4 oxidation was observed at soil moistures less than 325%(+/- 80%). CH4 emission was found at soil moistures exceeding this value. A large range of CH4 oxidation rates were observed over a small soil moisture range in the mineral soils. CH4 oxidation in mineral soils was negatively correlated with soil bulk density (Flux(CH4) = -37.35 x bulk density (g cm(-3)) +48.83, p < 0.05). Increased nitrogen loading of the soil due to N fixation, atmospheric deposition of N, and fertilisation, were consistently associated with decreases in the soil sink for CH4, typically in the range 50 to 80%, on a range of soil types and land uses.