Estimation of CO₂ diffusion coefficient at 0–10 cm depth in undisturbed and tilled soils

Abstract

Diffusion coefficients (D) of CO₂ at 0–10 cm layers in undisturbed and tilled soil conditions were estimated using the Penman (Penman HL. 1940. Gas and vapor movement in soil, 1. The diffusion of vapours through porous solids. J Agric Sci. 30:437–463), Millington–Quirk (Millington RJ, Quirk JP. 1960. Transport in porous media. In: Van Baren FA, editor. Transactions of the 7th International Congress of Soil Science. Vol. 1. Amsterdam: Elsevier. p. 97–106), Ridgwell et al. (Ridgwell AJ, Marshall SJ, Gregson K. 1999. Consumption of atmospheric methane by soils: A process-based model. Global Biogeochem Cy. 13:59–70), Troeh et al. (Troeh FR, Jabro JD, Kirkham D. 1982. Gaseous diffusion equations for porous materials. Geoderma. 27:239–258) and Moldrup et al. (Moldrup P, Kruse CW, Rolston DE, Yamaguchi T. 1996. Modeling diffusion and reaction in soils: III. Predicting gas diffusivity from the Campbell soil–water retention model. Soil Sci. 161:366–375) models. Soil bulk density and volumetric soil water content (θ_v) at 0–10 cm were measured on 14 April, 2 June and 12 July 2005 at 0–10 cm depth in no-till (NT) and conventional till (CT) malt barley and undisturbed soil grass–alfalfa (UGA) systems. Air-filled porosity (ε) was calculated from total soil porosity and θ_v measurements. Both soil air porosity and estimated CO₂ diffusivity at the 0–10 cm depth were significantly affected by tillage. Results of CO₂ diffusion coefficients in the soil followed trends similar to those for soil ε data. The CT tended to have significantly greater estimated soil CO₂ diffusion coefficients than the NT and UGA treatments. The relationship between D/D ₀, and air-filled porosity was well described by a power (R ² = 0.985) function. The model is useful for predicting CO₂ gas-diffusion coefficients in undisturbed and tilled soils at various ranges of ε where actual gas D measurements are time-consuming, costly and infeasible.

Keywords:

• soil
• tillage

Acknowledgements

The authors wish to express their thanks and appreciation to Mr John Rieger, Mr Bryan Gebhard and Mrs Amy McGregor for their assistance in weekly CO₂ measurements, soil sampling and properties measurements. The helpful comments and suggestions of the Editor in Chief, Dr Heirun Beschow and two anonymous reviewers are greatly appreciated.