Effect of amendment on Cd uptake by Brassia chinensis in Cd-contaminated soils

The effects of 4 amendments lime, calcium-magnesium phosphate (Ca-Mg-P fertilizer), alkali slag and peat on biomass, Cd uptake of Brassia chinensis, and pH and DTPA-extracted Cd in Cd-contaminated soils were investigated in a pot experiment of two continuous crops of B. chinensis. The results show insignificant effects on B. chinensis biomass of additions of 1 mg·kg^-1 and 5 mg·kg^-1Cd. However, some form of promotion of biomass is noted under 1 mg·kg^-1 Cd addition. Amendments do not significantly improve biomass, but remarkably decrease shoot Cd content in B. chinensis in Cd-polluted soils. The order of efficiency of the 4 amendments on reducing shoot Cd content is lime≈peat>alkali slag>Ca-Mg-P fertilizer. 4 amendments present different Cd-reduction effects on B. chinensis root. In the first and second crop, peat and lime decrease root Cd under all Cd treatments, while Ca-Mg-P fertilizer shows the same effect only under 0 and 1 mg·kg^-1 Cd. Alkali slag shows not effect. There is a significantly negative correlation between soil DTPA-extracted Cd and pH. Lime, peat and Ca-Mg-P fertilizer increase soil pH, and decrease DTPA-extracted Cd, resulting in decreasing shoot Cd content in B. chinensis. Peat increases soil pH, but does not decrease DTPA-extracted Cd as much as pH. The main mechanism of Cd-reduction effect of peat on B. chinensis shoot could be related with the formation of organic-chelated Cd, which is difficult for B. chinensis to uptake. Comparison between the two crops indicates that amendments have a significantly decreasing effect on Cd content in B. chinensis in the second crop.