Influence of soil drying followed by flooding on micronutrient solubilization

Flooding is known to solubilize soil nutrients, particularly those associated with redox-sensitive metals (Fe/Mn). Both soil flooding and drying are becoming more common due to climate change, but it is not clear how soil drying prior to flooding influences nutrient solubilization in soils, compared with flooding of already moist soils. This study was designed to examine how soil drying followed by extended flooding might influence solubilization of micronutrient metals (Fe, Mn, Cu, Co, Zn and Ni). A series of laboratory mesocosm experiments was carried out by flooding samples of two contrasting grassland soils, which had each been either dried (40°C for 10 days) or kept at field moisture conditions (25%, w/w). The flooding of dried soils generally resulted in higher concentrations of the micronutrients (Mn, Co, Ni and Cu) in the water columns relative to their moist-flooded counterparts. The results demonstrate that the flooding-induced variations in pH and redox potential influence solubilization of micronutrients in the soils. The mobilization of Co and Ni appeared to be controlled by redox-driven reductive dissolution of Fe/Mn minerals. This was supported by significant (p < .001) negative correlations between redox and metals: Co (r = −.712), Ni (r = −.784) and the positive correlations between Fe and metals: Co (r = .763) and Ni (r = .714) and between Mn and other metals: Co (r = .909) and Ni (r = .811). However, there were no significant correlations of Zn and Cu with Fe and Mn. The results suggest that soil drying followed by flooding has the potential to promote greater solubilization of soil micronutrients compared with flooding of moist soils, with potential implications for soil fertility and catchment water quality under future changes in weather patterns driven by climate change.