Soil Tillage Impact on the Diurnal Redox-Potential Cycle
Tillage-induced changes in soil physical properties affect the chemical and biological properties of that soil. The objective of this study was to determine the influence of soil tillage on the structure of redox-potential cycles in the field. Platinum electrodes and Cu-constantan thermocouples were installed under two field treatments (rototillage/residue incorporated or no-tillage/surface residue) at 7-, 15-, and 22-cm soil depths, and readings taken at intervals of 2 and 3 h during the 1986 growing season. During the early part of the corn (Zea mays L.) growing season, water evaporation was minimal and soil temperatures were higher in the rototill than the no-till treatment. At this time, a unique relationship existed between soil temperatures and redox potentials that could not be explained by only the influence of the diurnal soil-temperature cycle on O₂ diffusion. In the rototillage treatment, minimum redox potentials were observed when soil temperatures were 23 and 18 °C at the 7- and 22-cm soil depths, respectively. In the no-tillage treatment, minimum redox potentials were observed when soil temperatures were 19, 18, and 16 °C at the 7-, 15-, and 22-cm soil depths, respectively. Increases or decreases from temperatures where minimum redox potentials were observed resulted in increased redox potentials. A simulation study suggested that, at these temperatures, microbial O₂ consumption was at a maximum. During a later part of the growing season, water evaporation was high and on a diurnal cycle, and both redox potentials and soil temperatures followed diurnal cycles. The diurnal structure observed in the redox-potential cycles could be explained by considering the influence of diurnal water-contents cycles on O₂ and substrate diffusion.
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