**Acknowledgements**

μg g−1 soil respectively [100]. These results demonstrated that *Brassica juncea* had the ability to survive and tolerate several metals simultaneously, in the presence of high levels of Na and Mg (SAR between 2.5 and 3.7% and ESP between 18.3 to 20.7%) [100]. All metals measured from mine tailings were accumulated in the root and there was very low translocation to the

According to the literature, the typical behavior of an accumulator species such as *Brassica* is that there is higher accumulation of heavy metals in the leaves [101], which is opposite to the

Results suggest that high levels of Na and salt in mine tailings and the physicochemical characteristic of mine tailings might influence translocation of heavy metals from roots to shoots; metals such as Pb and Zn which are the main metals extracted by *Brassica juncea*. This suggestion is according to reports showing that salt acts antagonistically, thus when plants grow in media with a high Pb concentration and high salt concentration, the amount of Pb

The mine tailings amended with 10% compost to growth two shrubs *Acacia retinodes* and *Nicotiana glauca* were able to survive at high concentrations of heavy metals in mine tailings (**Table 1**) when 10% compost was added. The dry biomass of both shrubs increase from 62 to 79% growth in mine tailings plus compost compared to mine tailing alone. *Echinochloa polystachya* was not able to grow on mine tailings, even when it was amended with compost, as was shown by the percentage inhibition data for its root and leaf biomasses. Pb and Zn concentrations in the three plants were higher in roots compared to leaves for all treatments (Pb from 514 to 861 in roots and from 14.6 to 90 (μg g−1) in leaves and Zn from 682 to 766 in roots and 541.4 to 254 (μg g−1) in leaves) [70]. The elevated contents of Pb and Zn in roots along with the low translocation factors [70] indicate that the two shrub species used in this study

The drastic decrease in soil organic matter in semi-arid soils due to deforestation or in some areas used as deposits for mine tailings are attractive sites for soil restoration. These areas need application of organic residues to avoid subsequent soil erosion by losing soil structure and minimize high risk of pollution in adjacent areas. Application of organic wastes may provide nutrients to pioneering vegetation increasing organic content and improving soil physico‐

This work provides a clear demonstration of the role of organic waste to increase or release heavy metals according to the quality of organic matter amendment. Recycling valuable components such as C and N available in semi-arid soils was supported by the potential C and N mineralization, dehydrogenase activity, and plant growth. Retention of heavy metals on the fractionation of organic matter cannot be generalized, it will depend on the chemical charac‐ terizations of organic waste and soil. Chemical characteristics of the organic waste such as the

shoots.

results of these study.

**4. Conclusions**

accumulated by *Brassica juncea* decreases [102].

262 Organic Fertilizers - From Basic Concepts to Applied Outcomes

are appropriate for Pb and Zn phytostabilization.

chemical and biological properties and thus their natural fertility.

This work was financially supported by Semarnat-Conacyt, 2002-COI-0184, and FOMIX Zacatecas: ZAC-COI-82037, Mexico. The author would like to thank J. Corona-Hernández for his help in computational tools
