RELATIONSHIPS AMONG OXYGEN FLUX, SOIL WATER TENSION, AND AERATION POROSITY IN A DRYING SOIL PROFILE1

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Abstract
A Captina silt loam (Typic Fragiudult) was nearly saturated and allowed to dry by drainage and evaporation. O2 flux and soil water tension were measured simultaneously on 2 bare plots during 3 drying cycles. At the end of the study, undisturbed cores were taken at 3 depth intervals in 2 plots and aeration porosity characteristics were determined. The functional relationships between O2 flux and aeration porosity determined from tensiometer data in the field and between tension and aeration porosity determined from the undisturbed cores were used to derive the mathematical relation between O2 flux and soil water tension for the Captina profile. For the Captina soil, aeration porosity increased linearly with the natural logarithm of soil water tension. Similarly, the natural logarithm of O2 flux was linearly related to aeration porosity. The combined equation describing O2 flux as a function of soil water tension in the Captina soil constituted a power function. The description of the field data by the derived equations was excellent at all depths, there was close agreement between the derived and the regression parameters of the power function relating O2 flux and soil water tension.