Abstract: In the current research, an incubation experiment was conducted to test the passivation effect of biochar (B), sepiolite (S) and phosphorite (P) in combination of urea application on cadmium (Cd) availability in order to explore the effective materials for the development of Cdpassivation fertilizers. The results showed that surface area, specific surface area and functional group of passivators B, S and P were all increased after acid modification. Compared to the treatments without application of passivators, all the treatments with application of passivators alone or in combination decreased available Cd content, among which, S+P exhibited the best passivation effect, and available Cd content decreased by 23%. Compared to the application of urea alone, the application of urea combined with passivators decreased available Cd content and S+P treatment showed the best effect. Passivator addition can alleviate soil acidification caused by the ureaN transformation, increase the soil pH, and reduce the availability of Cd to a certain extent. The results suggest that acid modified P and S can be used in the development of new type toxic metalpassivation fertilizers.

Key words: dissolved organic matter, precipitation exclusion, warming