Evaluating aeration criteria by simultaneous measurement of oxygen diffusion rate and soil-water regime

Adequate aeration is important for plant root growth. The purpose of this paper was to evaluate aeration criteria by examining the relationships between oxygen diffusion coefficient (ODR) and soil-water potential, soil-water content, air-filled porosity, and gas diffusion rate. In this study we used undisturbed columns and cores of four soils representing different textures (Delhi loamy sand, Arlington sandy loam, Sorrento clay loam, and Imperial silty clay). The ODR was measured under variable soil-water potential conditions. Other aeration parameters, such as oxygen diffusion coefficient (D-p) and air-filled porosity, were calculated based on soil-water content, bulk density, and particle density. Soil-water potential, soil-water content, air-filled porosity, and gas diffusion coefficient at the threshold ODR value of 0.2 mug cm(-2) min(-1) that provided satisfactory aeration status were evaluated in the four different soils. The threshold ODR value occurred at different soil matric potentials, volumetric water contents, air-filled porosities, and relative gas diffusion coefficients (D-p/D-o) for the four test soils, depending on their texture and bulk density. The relationships between ODR and soil-water potential, soil-water content, air-filled porosity, and gas diffusion coefficient were found to be different for the four test soils. All of these results indicate that comparing air-filled porosity and diffusion coefficients at the field capacity for different soils offers little information about the soil aeration capability that influences plant growth directly. We concluded that ODR, a measure that mimics the oxygen supply to root surface, should be used instead for evaluating soil aeration capability.