Field evaluation of in situ remediation of Cd-contaminated soil using four additives, two foliar fertilisers and two varieties of pakchoi

• Effects of four additives combined with two foliar fertilizers were evaluated.
• RM and SP showed excellent ability to reduce Cd accumulation in pakchoi.
• Ca and Zn could reduce Cd accumulation in pakchoi.
• Ca and Zn could not help additives reduce Cd accumulation, except for CMP.

This study was conducted to determine the optimal planting mode for pakchoi (Brassica rapa chinensis) in Cd-contaminated soil to reduce the accumulation of Cd in the edible parts while maintaining yields. Four additives (red mud (RM), silicon calcium fertiliser (SC), spodium (SP) and calcium magnesium phosphate (CMP)), two foliar fertilisers (Ca and Zn) and two varieties of pakchoi (Aijiaohuang (AJ) and Baixuegongzhu (BX)) were used in this study. The results show that the addition of SC and RM had an effect, but the other additives did not appear to increase the biomasses of AJ and BX. In some cases, the growth responses of AJ and BX to the same treatment were different. Extra additions of Ca or Zn to additive-treated pakchoi did not help the additives stimulate the growth of AJ and BX, except for SC-treated AJ and BX and SP-treated AJ. The SC and CMP additives significantly reduced the available Cd concentration in both the AJ soil and the BX soil; however, they did not significantly decrease the Cd concentration in the aboveground parts of AJ and BX. The RM treatments (for both levels) and some treatments containing SP reduced the available Cd concentration in the soils and reduced the accumulation of Cd in the two pakchoi varieties. Additions of Ca or Zn fertiliser significantly reduced the Cd concentration in the aboveground parts of AJ and BX. However, when Ca or Zn was sprayed on the additive-treated AJ and BX, they did not help the additives reduce the Cd accumulation in the aboveground parts of AJ and BX, except for the additive CMP. This study shows that RM may be an optimal amendment to reduce the accumulation of Cd in the edible part of pakchoi while simultaneously maintaining yields. The utilisation of Ca or Zn as a foliar fertiliser to additive-treated pakchoi showed positive effects only under some conditions.