MEASUREMENT OF GAS-DIFFUSION COEFFICIENT UNDER RELATIVELY LOW AIR-FILLED POROSITY

Knowledge of the diffusion coefficient is necessary for modeling gas movement through soil. Various equations have been proposed relating apparent gas diffusion to soil parameters. A laboratory study was conducted to measure gas diffusion through soil at low air-filled porosity (0. 05, 0. 10, and 0. 15) using an inert gas (Freon: CCl//2F//2). The Penman model D//s/D//A equals 0. 66a, where D//A and D//S are gas diffusion coefficients in air and soil, respectively and a is S volumetric soil air content, greatly overestimated the measured D//s at all porosities. The Millington-Quirk model D//S/D//A equals a **3**. **3**3/ phi **2, where phi is the soil porosity, had the same curve shape but slightly underestimated the measured D//S. Much better agreement between calculated and measured D//S was obtained by reducing the exponent 3. 33 in the Millington-Quirk model to 3. 10.