The soil water content was calculated as the difference in weight of a 15 g fresh soil sample before and after drying at 105 °C for 24 h. The soil pH was measured using the hydrometer method with deionized water [water:soil = 2.5 (v):1 (m)]. The soil Fe2+content was measured using phenanthroline spectrophotometry using an ultraviolet/visible light photometer (UV-2450, SHIMADZU, Kyoto, Japan).