The total soil methane emission is calculated as the sum of ebullition (), plant transport (), diffusive flux through soil air () and aerodynamic exchange between soil surface and atmosphere ():
The first three terms are calculated as direct emissions from each soil layer.
Since gas conducting plants are capable of transporting atmospheric oxygen down to the roots, an efficiency parameter (CH4 PlantOxidationEff) has been introduced to calculate effective methane emission from plants (Gerard, 1993).
The diffusive flux through air is calculated for each layer as:
where ∆z is the distance from the middle depth of one layer (I) to the middle depth in the layer above (I-1), CCH4a is the methane concentration in air and f(O2) is an oxygen diffusion exchange function.
The emission from the uppermost layer is calculated as:
where CCH4a(1) is the methane concentration in air in the uppermost layer, CCH4atm is the concentration in atmosphere (CH4 AirConc), ras is the aerodynamic resistance above soil surface and ρCH4 is the density of methane.