Gas diffusion and

soil physicals properties in large soil monoliths

Lange Sébastien et Allaire Suzanne

Département des sols et de génie agro-environnemental

Université Laval, Québec, Canada

Gas diffusion in soil is affected by different soil properties including structure, texture, water and air contents. Gas diffusion has rarely been measured at scale larger than a few centimetres. The objective of this study is to experimentally determine relative gas diffusion coefficient with large undisturbed soil cores (0.45 m diameter and 0.4 m depth) as affected by soil physicals properties. Three intact replicates of an organic soil and a fine sandy soil were extracted from fields. A gas injection chamber and a subdivided flux chamber were installed at each end of the monoliths. Neon was injected and its concentration was maintained constant in the injection chamber for 48 hrs. Atmospheric pressure was maintained throughout the system to avoid convective fluxes. Gas samples were withdrawn in 5 sections, 3 depths and 7 heights in each columns many times until gas was detected in sufficiently high concentration in at least one section of the flux chamber. Samples were analysed on GC. Soil samples were taken from the monoliths for water content, structure, granulometry, organic carbon content, and bulk density measurements at the same sections and depths. Observations were completed on macroporosity and other heterogeneities (stones, roots, worms, etc.). Diffusion coefficient will be calculated for the different sections and depths. Variability in diffusion within monoliths, between replicates and between soils will be discussed. Stepwise regressions and cross correlation statistical analysis will be used to relate diffusion and soil physical properties. Application of these findings to interpretation of field studies and the use of small samples will be discussed.