Temporal Pattern of Oxygen Concentration in a Hydromorphic Soil

Abstract

AbstractOxygen deficiency negatively affects crop yield and has a major impact on soil biological activity. This work was performed to ascertain the factors affecting the O2 concentration in a soil profile, and to analyze the hypothesis used in O2 transport models. Oxygen concentration was measured using platinum microelectrodes. Soil porosity, water content, temperature, groundwater depth, and microbial respiration were analyzed as the driving variables affecting O2 concentration. Soil respiration was well described by a Michaelis kinetics; the maximal rate of respiration for the 0‐ to 0.1‐m layer (2.5 × 10‐5 mol m‐3 s‐1) was five times higher than for the 0.3‐ to 0.5‐m layer. This implies that the simplification of vertical homogeneity and zero‐order kinetics for O2 consumption are invalid to estimate O2 transport. In the topsoil, the amplitude of the changes in O2 concentration after rainfall decreased in the order autumn > winter > summer. At 0.2 m for rainfall of ≈40 mm, the O2 concentration decreased 0.09 m3 m‐3 within 3 d after rainfall in autumn, and 0.05 m3 m‐3 within 6 d in winter. The fluctuations observed in O2 concentration after rainfall indicated that the steady‐state approximation used in models is too restrictive to describe O2 transport in soil. In the subsoil, O2 concentration varied slightly due to low O2 consumption (≈10‐7 mol m‐3 s‐1). Oxygen concentration in the topsoil was negatively associated with the water‐filled pore space, except for measurements taken immediately after rainfall >30 mm d‐1, which indicated the presence of entrapped air. This suggests that the hypothesis of instantaneous equilibrium between water content and soil O2 concentration is a reasonable simplification except for the 12‐ to 24‐h following high‐intensity rainfall.