As some trace elements (TEs) are essential micronutrients for all living organisms, their availability in soils is important for sustaining a healthy ecosystem. The objective of this study was to test the hypothesis that the intensity, duration, and frequency of soil drying-rewetting cycles enhance leaching of TEs (Mn, Zn and Cu).

We tested this hypothesis by drying a loamy grassland soil at 4 temperatures (25°C, 30°C, 35°C and 40°C) and two durations (2 or 14 days). Subsequently two replicates of each dried soil treatment plus a moist control treatment were packed in microcosms and rewetted with deionised water. All treatments were subjected to three re-wetting cycles. Second and third rewetting cycles were carried out 7 days after the first and second rewetting events, respectively. Collected leachate was filtered (0.45µm), acidified (Aristar HNO₃) and analysed for TEs, using ICP-MS.

Relative to the control moist soil (39.7 % moisture content and stored at 3°C), the leachate concentration of all metals increased in all drying treatments. The largest percentage metal concentration increases occurred for the extended drying period (14 days) at 40°C. However, smaller increases in leachate metal concentrations were observed for the shorter drying duration (2 days) at 40°C. The observed increase in metal leaching is perhaps caused by drying-rewetting induced aggregate disruption, enhanced mineralisation, and microbial cell lysis. Our results demonstrate that the intensity and duration of drying enhance concentrations of Mn, Zn and Cu in leachates. However concentrations diminished in the successive rewetting events probably because available metals have been leached and those that remain were not in soluble forms.

Our results suggest that increased intensity and duration of soil drying and frequency of successive rewetting have potential to promote leaching of TEs and thus have implications for ecosystem health, especially under changing climate.