PORE CHARACTERISTICS OF SOILS FROM TWO CULTIVATION EXPERIMENTS AS SHOWN BY GAS DIFFUSIVITIES AND PERMEABILITIES AND AIR‐FILLED POROSITIES

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Abstract
Summary: Gas diffusivity and permeability, and air‐filled porosity, were measured in undisturbed soil cores at six water potentials between ‐2 kPa and oven dryness. All increased as water potential fell. In silt loam at 30 to 80 mm depth, relative diffusivity and air permeability at ‐2 kPa were 0.0013 and 5 × 10−8cm2 after direct drilling, and were 6 and 15 times greater respectively after ploughing, presumably because of the larger volume of air‐filled large pores in the ploughed soil. These pores may also have been more continuous or less tortuous than in the direct drilled soil. However, at equal air‐filled porosities up to 0.18 v/v, the pores were apparently more continuous and less tortuous in the direct drilled than in the ploughed soil. In the direct drilled silt loam at any given matric potential, air‐filled porosity, gas diffusivity and permeability within and below the previously ploughed layer were isotropic. In clay loam at 30 to 80 mm depth gas diffusivity and permeability at ‐2 kPa were greater than in the silt loam irrespective of tillage but increased less on oven drying.