Abstract: Lead (Pb) and cadmium (Cd) contaminated soil in a farmland in Shaoguan City, Guangdong Province was studied. A pot experiment was conducted to study the effects of single and multiple application of lime (w=0.2%) and humic acid (w=1%, 2% and 5%) to Pb and Cd contaminated soil on soil physical and chemical properties, available Pb and Cd content, Pb and Cd absorption and growth of ryegrass (Lolium perenne). Based on this, the regulation efficiency of lime and humic acid on Pb and Cd bioavailability in soil was discussed. Results show that the soil pH could be improved by the application of single lime or lime combined with humic acid treatment, while the concentrations of available Pb and Cd in soil was significant reduced. Especially, as compared with control, the content of available Pb and Cd decreased by 89.45% and 89.63%, respectively, when lime was mixed with 5% humic acid. There was a significant increase in the content of soil organic matter and the growth of ryegrass with application of single humic acid or lime combined with humic acid. There was a significant decrease in the absorption of Pb and Cd by ryegrass. The Pb absorption in the aboveground part of treatment with lime + 5% humic acid was significantly lower than those of other treatments, which was about 48.52% lower than that of the control. The Cd absorption in the aboveground part of treatment with single 5% humic acid was significantly lower than those of other treatments, which was about 59.62% lower than that of the control. Besides, the regulation efficiency of bioavailability of Pb and Cd in soil by the combined application of lime and humic acid was better than that of single humic acid or lime. There was a significant interaction between lime and humic acid.

Key words: lime, humic acid, ryegrass (Lolium perenne), combined contamination of lead and cadmium