Abstract
Soil-gas diffusivity plays a fundamental role on diffusion-controlled
migration of climate impact gases from different terrestrial ecosystems
including managed pasture systems. Soil-gas diffusivity has a strong
bearing on soil type/texture and soil structure (e.g., density) and
typically shows a depth-dependent behavior in subsurface. This study
investigated the gas diffusivity in soils sampled from a managed pasture
site at Ambewela, Sri Lanka at 0-5 cm depth range along a downgrading
transect. The soils were pre-characterized for particle-size
distribution, organic matter content, dry density and particle density.
Soil-gas diffusivity was measured using one-chamber diffusion apparatus
using N2 and O2 as experimental gases. The measured diffusivity,
together with selected intact and repacked soil data from literature,
were tested against the existing predictive gas diffusivity models. We
used a generalized descriptive parametric two-region model to represent
bimodal/two-region behaviour of selected soils which was able to
statistically outperform the predictive models for both intact and
repacked soils and hence demonstrated its applicability to better
characterize site-specific greenhouse gas emissions with useful
implications for pasture management.