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Identification of reducing conditions in soils is of concern not only for pedogenesis but also for nutrient and pollutant dynamics. We manufactured manganese (Mn)-oxide-coated polyvinyl chloride bars and proved their suitability for the identification of reducing soil conditions. Birnessite was synthesized and coated onto white polyvinyl chloride bars. The dark brown coatings were homogenous and durable. As revealed by microcosm devices with adjusted redox potentials (E), under oxidizing conditions (E ∼450 mV at pH 7) there was no Mn-oxide removal. Reductive dissolution of Mn-oxides, which is expressed by the removal of the coatings, started under weakly reducing conditions (E ∼175 mV) and was more intensive under moderately reducing conditions (∼80 mV). According to thermodynamics, the removal of Mn-oxide coatings (225 mm d) exceeded the removal of iron (Fe)-oxide coatings (118 mm d) in soil column experiments. This was confirmed in a soil with a shallow and strongly fluctuating water table where both types of redox bars were inserted. Consequently, it was possible to identify reducing conditions in soils using Mn-oxide-coated bars. We recommend this methodology for short-term monitoring because tri- and tetravalent Mn is the preferred electron acceptor compared with trivalent Fe, and this additionally offers the possibility of distinguishing between weakly and moderately reducing conditions. If dissolved Fe is abundant in soils, the possibility of nonenzymatic reduction of Mn has to be taken into account.

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Plant roots are inhabited by microbial communities called the root microbiota, which supports plant growth and health. We show in a maize field study that the root microbiota consists of stable and dynamic members. The dynamics of the microbial community appear to be driven by changes in the metabolic state of the roots over the life cycle of maize.

Summary The soil water content affects rates of oxygen diffusion and redox potentials (EH). When water‐saturated soils become aerated, a switch from reducing to oxidizing conditions occurs. However, limited information is available on the air‐filled pore volume (ϵ) at which this shift happens. To obtain values of ϵ, undisturbed soil cores were taken from a Fluvisol and a Gleysol that differed in structure and clay content. Experiments on submergence and drying following a new experimental design were performed in the laboratory. After submergence, the cores were sealed with a glass hood to exclude oxygen and to achieve reducing conditions (EH < −100 mV). We then aerated the sample by removal of glass plugs in the hood and measured EH consecutively by platinum (Pt) electrodes and ϵ by matric potential readings on an hourly basis. From the drying curve we determined two characteristic values: (i) ϵPt reaction indicates the air‐filled pore volume at which a response of the Pt electrode to contact with oxygen occurs (i.e. EH increase > 5 mV hour−1) and (ii) ϵPt aeration indicates when oxidizing soil conditions are present (i.e. EH > 300 mV at pH 7). The Fluvisol was characterized by an ϵPt reaction value of 0.036 ± 0.006 cm3 cm−3 and an ϵPt aeration value of 0.047 ± 0.005, whereas for the Gleysol these values were 0.048 ± 0.008 and 0.085 ± 0.007 cm3 cm−3, respectively. We aimed to obtain such characteristic values for different soils to estimate the aeration status of a soil when ϵ is known, but EH measurements were unavailable. Highlights We studied the relation between EH and air‐filled pore volume (ϵ) for two soils varying in texture. Two characteristic ϵ values are proposed: ϵPt reaction (EH increases > 5 mV hour−1) and ϵPt aeration (EH > 300 mV at pH7). ϵPt aeration was larger for a clayey Gleysol than a sandy Fluvisol, but ϵPt reaction was similar. Small‐scale heterogeneity in soil structure had no effect on the EH–ϵ relation.