Measurements of diffusive and convective gas transport parameters can be used to describe soil functional architecture and reveal key factors for soil structure development. Undisturbed 100-cm3 soil samples were sampled at the Long-term Research on Agricultural Systems experiment located at the University of California, Davis. The 18 plots used in this study represented fairly wide ranges in organic carbon (0. 0072–0.0153 kg kg−1) and clay (0.30–0.44 kg kg−1). Soil-air permeability, ka, and soil-gas diffusivity, DP/D0, were determined at field-moist conditions (fm) and, subsequently, after saturation and drainage to −100 cm of matric potential (pF2). Gas diffusivity in intact samples at fm conditions exhibited a general, linear relationship with air-filled porosity ([Latin Small Letter Open E]), independent of soil texture and treatment. Comparing intact and repacked samples drained to pF2, repacked soil displayed markedly lower DP/D0 values at similar air-filled porosity, illustrating soil structure effects on DP/D0. The Currie tortuosity-connectivity parameter, X = Log(DP/D0)/Log([Latin Small Letter Open E]), decreased with increasing bulk density in the intact samples at both moisture conditions, suggesting less tortuous and well-connected pathways for gas diffusion at higher bulk density. Pore organization, PO = ka / [Latin Small Letter Open E], showed a treatment effect with typically higher values for the organic plots, implying that an improved possibility for formation of organomineral soil aggregates resulted in better-connected macropore networks. Fitting a linear model to DP/D0 versus [Latin Small Letter Open E] measurements revealed different slopes at the two moisture conditions, suggesting short-term nonsingularity (hysteretic) effects after rewetting and drainage. Defining the ratio of slopes at the fm and pF2 moisture conditions as a nonsingularity index (α), the nonsingularity in DP/D0 increased with lower bulk density and higher organic carbon content.
1Dept. of Agroecology, Aarhus University, Tjele, Denmark;
2Dept. of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Aalborg, Denmark;
3Dept. of Land, Air & Water Resources, University of California, Davis, CA
Address for correspondence: Marie Eden, PhD, Dept. of Agroecology, Aarhus University, Blichers Allé 20, Post Box 50, DK-8830 Tjele, Denmark. E-mail: firstname.lastname@example.org
Financial Disclosures/Conflicts of Interest: None reported.
Received December 28, 2011.
Accepted for publication July 3, 2012.