Field scale remediation of Cd and Pb contaminated paddy soil using three mulberry (Morus alba L.) cultivars

Mulberry tree (Morus alba L.) is an effective material available for the remediation and utilization of heavy metal contaminated soil. A three-year experiment was carried out to assess the effects of three mulberry varieties under three planting densities on the removal of Cadmium (Cd) and lead (Pb). Meanwhile, the pollution levels of the farmland by Cd and Pb were also evaluated. Results showed that the soils were strongly to extremely polluted by Cd and moderately to strongly contaminated by Pb. The biomasses of mulberry trees were increased with the increasing planting densities both in 2014 and 2015, except the biomasses of Nongsang 14 in the planting density 30,000 plants/hectare (ha) in 2014. The total biomasses of Yuesang 11 were the highest among the test three cultivars. In addition, the concentrations of Cd and Pb in the root were much higher than those in the stem or branch or leaf. One hectare mulberry shoots could extract 1.92-7.89 g Cd and 9.70-83.58 g Pb every year, respectively. The three mulberry varieties were all not hyperaccumulators for Cd or Pb because both the bio-concentration factors (BCFs) and translocation factors (TEs) were less than 1. These results indicated that mulberry trees can be used as an alternative plant to make use of heavy metal polluted paddy soils and Yuesang 11 may be regarded as a candidate species for phytostabilization of Cd and Pb, with the planting density of 30,000 plants/ha.