Development and Tests of Predictive Soil-Gas Diffusivity Models for Japanese Undisturbed Soils

Abstract

Accurate description of gas diffusivity in undisturbed soil is required for predicting oxygen transport in cultivated soil and the fate of greenhouse gases and volatile organic chemicals. Based on measured data for 51 undisturbed soils, we developed three types of pedotransfer models for soil-gas diffusivity : (i) a model including the effect of pore-size distribution (Campbell type soil-water characteristic, SWC); (ii) a model including the effect of pore-size distribution and inactive (isolated) air-filled pore space ; and (iii) a simple power function model for use in case limited SWC data are available. The influence of selecting the reference air-filled porosity at either —100 and —63 cm of matric potentials(ε100 and ε63)on predicting soil-gas diffusivities was also examined. The new models were compared with recent predictive models such as the Millington-Quirk (MQ) model, the Buckingham-Burdine-Campbell (BBC) model, and Macroporosity-dependent (MPD) model. The widely-used MQ model generally underpredicted data. The new models as well as the BBC model and MPD model well predicted the measured soil-gas diffusivities, with the BBC model performing slightly better. There was no significant effect of including an inactive pore space term on predicted soil-gas diffusivities. In the new models, there was a tendency that the equations using ε100 as a reference point gave a better prediction of soil-gas diffusivities compared to the equations using ε63.