Soil drying-rewetting is known to enhance soil phosphorus leaching, which in part is due to osmotic shock and lysis of microbial cells upon rewetting. However, it is not entirely clear how this may be influenced by the intensity and duration of soil drying. We hypothesized that the intensity and duration of soil drying play important roles in determining the extent of dissolved reactive phosphorus (DRP) leaching resulting from microbial biomass mortality. To test this hypothesis soil sub-samples of a loamy grassland soil were dried (30 or 40 • C for 2 or 14-days), rewetted, and the leachate was analyzed for DRP. Soil drying at 30 • C for 2 and 14-days resulted in leachate DRP concentrations which were 71 and 271%, respectively, higher than those in leachate from a control moist counterpart. Relatively greater DRP leaching losses occurred from the soil dried at 40 • C for 2 and 14-days (143 and 300%, respectively). To determine the contribution of the microbial biomass to the DRP in leachate, soil sub-samples were fumigated with chloroform either before or after drying (30 or 40 • C for 2 or 14-days). All soil treatments were then either leached with water and analyzed for DRP or extracted with 0.5 M sodium bicarbonate solution and analyzed for microbial biomass phosphorus. Fumigating soil samples before or after drying reduced microbial biomass phosphorus. However, the effect of chloroform fumigation was more pronounced in terms of microbial biomass reduction in the DF (drying followed by fumigation) treatment. Moreover, results revealed that in the DF treatment, soils dried at 30 • C for 2-days and 14-days had 22 and 13%, respectively, more microbial biomass phosphorus than their counterparts dried at 40 • C for 2 and 14-days, respectively. These results suggest that soil drying at higher intensity and for prolonged periods significantly (p < 0.05) affect microbial biomass and subsequently increases soil phosphorus leaching following rewetting, due to enhanced contributions from the microbial biomass. These findings, however, need to be verified over a range of soil types under natural field conditions to better assess soil drying-rewetting effects on nutrient leaching.

Flooding is known to mobilise soil phosphorus (P). However, it is still not clear how climate change-driven extended periods of soil drying followed by flooding will affect soil-P dynamics. We tested the hypothesis under laboratory conditions that soil antecedent conditions (moist/dry) determine the amount of P mobilised upon flooding. A series of controlled laboratory experiments were carried out by flooding samples of two contrasting soils (a Dystric Cambisol [Crediton series] and a Stagni-Vertic Cambisol [Hallsworth series]), which had each been either dried (40 C for 10 days) or kept at field moisture conditions (25% moisture content). Flooding was simulated by maintaining a 10-cm water column depth in mesocosms. Periodically collected water samples were analysed for dissolved reactive P (DRP), total dissolved P (TDP) and dissolved unreactive P (DUP). The onset of flooding significantly (p < 0.001)

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.