Long-term Impact of Organic Amendments on the Bioavailability of Heavy Metals in Mudflat Soil and Their Uptake by Maize

Abstract

Organic amendments (OAs) can be a sustainable and effective method for mudflat soil improvement. A long-term field experiment was conducted to investigate the potential of OA application to mudflat soil improvement. We measured the pH, soil organic matter (SOM), salinity, maize growth, and heavy metal (HM) accumulation in OA-amended soils and maize tissues 23 months after three OAs, sewage sludge (SS), Chinese medical residue (CMR), and cattle manure (CM), were applied at the application rates of 0, 30, 75, 150, and 300 t ha-1. OA application significantly increased the SOM and decreased the salinity of mudflat soils. Additionally, CMR and CM application decreased soil pH. The maize biomass and HM contents in soil and maize increased after OA application. The bioavailability and bioconcentration of HMs were generally in the sequence of SS>CMR>CM. The average bioavailability ratios of HMs were in the order of Cd>Zn>Cu>Mn>Ni. The bioconcentration of Zn and Cd by maize was highest, followed by Mn, Cu, and Ni. SOM, pH, and salinity were the important factors regulating soil available HMs and, subsequently, HM accumulation in maize. Among the three OAs, SS is most effective in decreasing soil salinity and increasing the SOM, bioavailability and bioconcentration of HMs. On the other hand, CM was the best OA because it promoted significant maize growth yet maintained low HM contamination risk.