Gas diffusion through soil crumbs: the effects of compaction and wetting

Abstract

Samples of 1-2 mm crumbs from a clay loam under permanent pasture were equilibrated at -5 kPa water potential then compacted to varying degrees. Gas diffusion coefficients D, (hydrogen through air), were measured immediately on compaction, again after re-equilibration at -5 kPa, then at other water contents between saturation and dryness. The relationship between diffusion coefficient and air content, E , was, as elsewhere, in two parts (dD/dE small for drainage of pores within crumbs; large for pores between crumbs), but the transition from one part to the other occurred at smaller air contents with increased compaction. The air content at which D approached zero as the samples wetted was greatest in the loosest soil. Compaction from a bulk density of 0.86-1.29 g ~m -~ decreased the relative diffusion coefficient, DIDO (DO is the diffusion coefficient without impedance), from 0.35 to 0.22 (by 38%) at complete dryness, but from 0.19 to 0.035 (by 82%) in the soil initially at -5 kPa.On re-wetting and re-equilibrating at -5 kPa, DIDO decreased further to 0.008 (total 97%) because of extra water held in the now smaller pores of the compacted soil.No single relationship between D/Do and E fitted the results for even this one soil. CALL, F. 1957. Soil fumigation. V. Diffusion of ethylene dibromide through soils. Journal ofthe Science ofFood and Agriculture3,143-150. CURRIE, J.A. 1 9 6 0~. Gaseous diffusion in porous media. Part 1. A non-steady state method. British JournalofAppliedPhysics 11,314-311. CURRIE, J.A. 19606. Gaseous diffusion in porous media. Part 2. Dry granular materials. British Journal ofApplied Physics 11,3 18-324. CURRIE. J.A. 1961. Gaseous diffusion in porous media. Part 3. Wet granular materials. British Journal ofdpplied Physics 12,275-281.

Linear Model to Predict Soil-Gas Diffusivity from Two Soil-Water Retention Points in Unsaturated Volcanic Ash Soils

“…The decrease of C and v a, th with the increase in rd implies that at a given soil-air content within intermediate soil-moisture conditions (i.e., except at high soil-air contents) the soil-gas diŠusivity increased with a decrease in bulk density. This is in agreement with Currie (1984) . Lastly, the new 2RP model predicted excellently the measured D p values on repacked Nishi-Tokyo volcanic ash soils at three diŠerent bulk densities (Fig.…”

Combined Soil Physical Stress of Soil Drying, Anaerobiosis and Mechanical Impedance to Seedling Root Growth of Four Crop Species

“…This indicates that roots in the compact soil, such as hard pan layer, require a lower soil water potential (drier condition) for their favorable growth under the relatively wet environment. This result agrees with the general trends of relative diffusion coeffi cient (D/D 0 ) in a clay loam soil (Currie, 1984) and ODR in a silt loam soil (Agnew and Carrpw, 1985).…”

Oxidation of methane in boreal forest soils: a comparison of seven measures

“…We feel that the error lies in the coefficients used to adjust DCH4. These depend on both soil structure and moisture; Currie (1984) demonstrated that for a single soil type of varying moisture content no single relationship was satisfactory. In contrast, we are confident in our estimates for ACcH, in Equation 1 because soil CH, distributions similar to those in Fig.…”