Soil aeration: the relation between air‐filled pore volume and redox potential

Abstract

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.

System for quasi‐continuous simultaneous measurement of oxygen diffusion rate and redox potential in soil

“…) reflects small‐scale variations in soil aeration and redox status and is well in agreement with the findings by Dorau et al. (). They demonstrated small scale variations in re‐oxidation (increasing E H ) of microsites and a close linkage between E H and air‐filled pore volume (ε) in structured soil cylinders during air drying of the previously submerged soil samples.…”

Stable-Isotope-Aided Investigation of the Effect of Redox Potential on Nitrous Oxide Emissions as Affected by Water Status and N Fertilization

“…+ and NO 3 − along the soil profile varied in response to irrigation and fertilization (Figure 9b,c), similar to the study of Rubol et al [16]. Before fertilization, the soil Eh was low in the lower parts of the soil column (Figure 2b), since during the prolonged soil saturation the active soil microorganisms use alternative electron acceptors instead of oxygen [52][53][54]. Therefore, consistent with the high consumption rate of nitrate at −11 cm (Figure 9a), the Eh decreased even further and faster at −11 cm (Figure 2b).…”

Soil aeration and redox potential as function of pore connectivity unravelled by X‐ray microtomography imaging

“…Multiple water retention curves of soil samples from the same study site and the same depth have been obtained in a previous study. A detailed description can be found in Dorau et al (2018), which is also the conceptual and experimental basis for this study in conjunction with μCT 3D-image-analysis. We used the evaporation method with an HYPROP device (UMS, Munich, Germany) that measures a decrease in matric potential during evaporation of an initial water-saturated soil sample by two minitensiometers (5 mm Ø).…”

“…Recent statistical approaches to quantify biogeochemical heterogeneity derived from a multitude of E H readings are more than welcome (Wanzek et al, 2018). One approach to characterise the aeration status was proposed by Dorau et al (2018), where undisturbed soil samples were equipped in parallel with Pt electrodes to record the E H and micro tensiometers for the soil matric potential and thereupon calculate the air-filled pore space (ε). The authors identified soil-specific ε threshold values that characterise the ecologically important shift from anaerobic to aerobic soil microbial metabolism.…”

“…The authors identified soil-specific ε threshold values that characterise the ecologically important shift from anaerobic to aerobic soil microbial metabolism. Two characteristic ε values were defined: (i) ε Pt reaction indicated an initial diffusion of O 2 to which the Pt surface reacted (E H increase > 5 mV h À1 ) and (ii) ε Pt aeration enabled the assessment of the aeration status in terms of O 2 availability (E H > 300 mV at pH 7) (Dorau et al, 2018). These dramatic transitions from reducing towards oxidising soil conditions occur, for example, when water tables drop, perched water tables disappear, or irrigation is finished.…”