Lime and Phosphate Could Reduce Cadmium Uptake by Five Vegetables Commonly Grown in South China

A pot experiment was conducted in artificially Cd-contaminated (5 mg Cd kg(-1)) soils to investigate the feasibility of using lime (3 g kg(-1)) or phosphate (80 mg P kg(-1)) to mitigate uptake of Cd by vegetables. Five common vegetables in South China, including lettuce (Lactuca saliva L. var. ramosa Hort.), Chinese cabbage [Brassica rapa L. subsp. Chinensis (L.) var. parachinensis (L. H. Bailey) Hanect], Chinese broccoli (Brassica oleracea L. var. albiflora Kuntze), white amaranth (Amaranthus tricolor L.) and purslane (Amamnthus viridis L.), were grown in the soils and harvested after 60 d. The results showed that liming significantly reduced Cd uptake by most vegetables by 40%-50% (or a maximum of 70%), mainly due to immobilization of soil Cd. Increased availability of Ca in the soil might also contribute to the Cd uptake reduction as a result of absorption competition between Ca and Cd. Liming caused biomass reduction in white amaranth and purslane, but did not influence growth of the other vegetables. Phosphate decreased Cd uptake by vegetables by 12%-23%. Compared with lime, phosphate decreased, to a smaller extent, the bioavailability of Cd in most cases. Phosphate markedly promoted growth of vegetables. Changes in soil chemistry by adding lime or phosphate did not markedly influence nutrient uptake of vegetables except that lime increased Ca content and phosphate increased P content in shoots of the vegetables. The results suggested that a proper application of lime could be effective in reducing Cd uptake of vegetables, and phosphate could promote growth of the vegetables as well as alleviate the toxicity of Cd.