Abstract
Mobilization of phosphorus (P) in arable soils might be affected by groundwater fluctuations and the associated changes in redox potential (EH). However, the impact of systematic changes of EH on P mobilization in redoximorphic arable soils along a catena has not been studied so far. Therefore, we investigated P mobilization under different redox conditions in top- and sub-soil horizons of three groundwater affected arable soils along a slight slope (toe-, mid-, and upper-slope position) in Northern Germany using an automated biogeochemical microcosm system. The impact of pH, Al, Fe, Mn, and dissolved organic carbon (DOC) on P mobilization was also studied. The initial EH (+351 to +431 mV) and pH (6.5–7.0) decreased in all soil samples (EH = −280 mV; pH = 4.4) when creating a slurry. Thereafter, the pH increased to 7.1 and 6.4 with increasing EH in the mid-and toe-slope soil, respectively. Concentrations of dissolved P ranged between 20.8 mg L−1 under low EH in the toe slope topsoil and 0.69 mg L−1 under high EH in the toe- and mid-slop subsoil. Concentrations (mg L−1) of dissolved Fe (0.31–13.3) and DOC (92–2651) increased under low EH and decreased under high EH. The increase of P mobilization under low EH and pH in the soils might be due to the release of P via the reductive and acidic dissolution of Fe-(oxhydr)oxides and/or due to soil organic matter mineralization. The high mobilization of P under reducing conditions may increase its bioavailability; however, it may increase its loss in the soils, particularly in the toe slope profile.
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•Concentrations of dissolved P were higher under low than under high EH.•The reductive dissolution of Fe-oxides caused an increase in P mobilization.•Phosphorus was more mobilized in the toe-than the mid- and upper-slope soil.•Phosphorus was more mobilized in the top-than the sub-soil samples.•The loss of P is higher under reducing than oxidizing conditions.