A One‐Dimensional Physically Based Approach to Predict Soil Profile Aeration Requirements

Core Ideas A process‐based theory for predicting the minimum air‐filled porosity was developed. The model allows analyzing sensitivity of aeration requirements to system parameters. Common static air content values for entire soil profiles are shown to be flawed. A minimum air‐filled porosity (βmin) is necessary to allow sufficient gas influx and efflux without restricting the aerobic activities of roots and microorganisms. Fixed values for βmin are commonly used in crop growth and hydrological models, thus relegating the physical process of gas flow. We developed a process‐based approach to estimate the minimum air‐filled porosity along the soil profile, assuming the excess of CO2 to trigger the onset of deficit aeration. The developed set of equations is based on Fick's law and mass conservation and includes root depth and pore‐space tortuosity for gas diffusivity, rate of gas production over depth and soil gaseous diffusivity. The developed theory allows prediction of gas concentrations and aeration status for different boundary conditions. The minimum air‐filled porosity was shown to be dependent on profile depth and soil type, and in this respect commonly used fixed values for entire soil profiles would be flawed. When considering the pressure heads corresponding to these minimum air‐filled porosity, results showed an even higher dependence of soil type.