Moist soils were sieved (< 2 mm) and incubated at 45 % water holding capacity (WHC) and 25 °C for
7 days prior to use. The soils (100 g) were treated with 5 mL of CdCl2 or PbCl2 solutions to give the
heavy metals concentration at six different levels, which are 0.5, 1.0, 5.0, 10.0, 50.0 and 100.0 mg/kg Pb2+
with the constant concentration of 0.5 mg/kg Cd2+. Untreated soils were served as controls. The soil
moisture was adjusted to 60 % WHC with distilled water and then the soils were incubated at 25 °C and
kept darkness for 45 days. All treatments were replicated three times.