Effects of sludge product application on heavy metal enrichment in Isatis tinctoria under different canopy densities

Objective This paper aims to investigate the safety and quality effects in Isatis tinctoria grown under forests after applying sludge products.

Method I. tinctoria was planted under the forests after spreading 0 and 30 t/ha of sludge products at different canopy densities (0.3, 0.6, 0.8), respectively. The effects of different treatments on nutrient uptake, heavy metal enrichment and active ingredient content of medicinal parts of I. tinctoria at different growth stages were comparatively analyzed.

Result (1) The nitrogen, phosphorus and potassium contents in tissues of I. tinctoria were increased after applying sludge products, and the best improvement was total nitrogen content. (2) The enrichments in tissues of I. tinctoria for the heavy metals cadmium, arsenic and zinc were increased after applying sludge products. However, the enrichment in leaves of I. tinctoria for mercury decreased. (3) The content of active ingredients in root of I. tinctoria was reduced after applying sludge products, but the content of indigofera in leaves of I. tinctoria grown under heavy canopy density increased.

Conclusion The application of 30 t/ha sludge products at the current standard results in a high concentration of heavy metals in tissues of I. tinctoria, which affects the medicinal quality of I. tinctoria.