Keywords: 
• humic acid /
• compost /
• soil /
• zinc /
• lead /
• immobilization

Abstract: An indoor soil column cultivation experiment was carried out to investigate the effects of compost and humic acid on transformation of zinc (Zn) and lead (Pb). After adding 5% (by weight) humic acid, 10% (by weight) compost, and 5% humic acid and 10% compost together, the soil columns were cultivated in 9 replicates for 3 months. The water content in soil was kept to maintain 60% of field holding capacity at room temperature (25℃). Three replicates were sampled each month, and speciations of Zn and Pb were analyzed via a sequential extraction method. Both humic acid and compost, and their cooperating amendment, could significantly shift the forms of Zn and Pb in soil, which makes the transformation of exchangeable and carbonate fractions into organic and residual fractions. When compared with control, the humic acid and compost could reduce the exchangeable-Zn from 38%～51% to 14%～21% and 26%～46%, however, the percentage of Fe-Mn oxide fraction of Zn significantly increased from 23%～34% to 33%～56% and 26%～45%. The proportion of carbonate-Pb dropped from 12%～25% to 1%～15% and 2%～15%, respectively, the residual-Pb fraction boosted from 12%～14% to 32%～45% and 20%～23%. Different changes happened to other speciations, which indicated that either humic acid or compost could immobilize Zn and Pb in soil. Their cooperating effect was better than the individual using. We also found that no matter which one was used, it has better immobilization effect on Pb than on Zn.