Effect of calcium bentonite on Zn and Cu mobility and their accumulation in vegetable growth in soil amended with compost during consecutive planting.

In this study, greenhouse pot experiment was carried out to investigate the Cu and Zn mobility and their accumulations in pakchoi (Brassica chinensis L.) and Chinese cabbage (Brassica rapachinensis L.) growth in Ca-bentonite-pig manure co-compost (CBC)-soil system during three consecutive planting. Five composts (0, 2.5, 5, 7.5, and 10% Ca-bentonite-pig manure co-composts) amended soil with 5% (w/w) application rate and compared to control without any additive. The results showed that the addition of CBC increased the biomass and chlorophyll content of pakchoi, and the maximum overall yield was found in 7.5% CBC treatment (12.89 ± 0.25 g), while when compared with the 0% CBC (15.89 ± 0.52 g) treatment, the Ca-bentonite amendment slightly decreased the Chinese cabbage yield (14.65 ± 0.11-15.41 ± 1.97 g). Additionally, compared to the 0% CBC treatment (11.81 ± 0.57-25.75 ± 0.89 mg/kg), the Ca-bentonite amendments showed a positive effect on restraining the diethylene triamine penta-acetic acid Zn mobilization (4.43 ± 0.41-12.48 ± 2.54 mg/kg) in pakchoi and Chinese cabbage; beside this, no obvious effect was observed on DTPA-Cu. Furthermore, there were great potential impacts for plant-available Zn in Ca-bentonite amended treatments during the consecutive planting, which decreased the content of Zn in plants. DTPA extraction results showed significantly higher Cu and Zn contents in compost-soil mixture, but its availability for grown plant was not confirmed during the consecutive planting, because of the consecutive decrease heavy metals contents in crops. Overall, the Ca-bentonite could be a useful additive for restricting the heavy metal mobility and increase the pakchoi yield.