Methane fluxes on boreal arable soils

Methane (CH4) oxidation in soils is the only known biological sink of CH4. The sink strength of agricultural soils is known to be affected by soil properties and agricultural practices. We studied fluxes of CH4 in southern and northern Finland in arable soils with different texture and crops. The annual fluxes ranged from uptake of −1.2 kg CH4 ha−1 to emission of 40 kg CH4 ha−1. The CH4 oxidation decreased in the order loamy sand > well drained peat > clay > poorly drained peat. The more there were macropores or the less there were micropores in the soil, the higher was the mean annual CH4 oxidation rate. Calculated on the basis of the soil type specific CH4 flux rates from our study and the soil type distribution of Finnish agricultural soils, the total agricultural area in Finland would form an annual CH4 sink of −19 Gg CO2 equiv., which is 0.3% of the total reported greenhouse gas emissions from agriculture in 2004.