Effects of organic amendments on rice ( Oryza sativa L.) growth and uptake of heavy metals in contaminated soil.

Purpose: Previous studies showed that rapeseed cake increased rice grain yields and significantly lowered the heavy metal concentrations in the brown rice. The pH, dissolved organic carbon (DOC), and their dynamic changes in the soil solution have been seldom considered at different crop growth stages after organic amendments. Thus, the aim of the present study was to investigate the dynamic changes of soil solution and the mechanisms by which rapeseed cake (RSC) immobilized Cd and Cu in the soil-rice system. Materials and methods: A glasshouse pot experiment lasting 5 months during the rice ( Oryza sativa L.) growth season was carried out to ascertain the effects of three organic amendments (organic carbon material (OCM), RSC, and pig manure PM) on the growth and heavy metals uptake of rice at heavy metals mixed contaminated paddy soil. Several items were determined including pH, organic matter content, available P and K in soil, and total N, P, K, Cd, Cu, and Zn in the contaminated soil and amendments. Total and CaCl-extractable Cd, Cu, and Zn in different parts of rice crop in addition to pH, dissoluble organic carbon, and total Cd, Cu, Zn, and N in the soil solution were determined. Results and discussion: After application of RSC and PM to this contaminated soil, the DOC concentration in the soil solution from pre-tillering to booting stage increased, and then soil soluble heavy metal concentrations declined; thus, bioavailability declined result in the decreasing of Cd and Cu concentrations in the brown rice. RSC contains higher amounts of nitrogen compounds than OCM and PM, and the decomposition products of RSC increase dissolved organic nitrogen (DON) in the soil solution at tillering stages. The application of RSC reduced soil solution heavy metal concentrations at pre-tillering and tillering stages when rice crop was sensitive to heavy metal stress and resulted in higher grain yield and lower Cd and Cu concentrations in brown rice. The decline of heavy metal concentration in soil solution resulted from the adsorption, complexation, and precipitation reactions by the decomposition products. Conclusions: In summary, the application of RSC resulted in a rise of DOC and DON concentration in the soil solution of rice crop which reduced heavy metal concentrations in soil solution and lowered the heavy metals bioavailability. Our results suggest that RSC was effective in immobilizing metals in soil and alleviation of their toxicity to rice crop, and thus can be used to amend the Cd- and Cu-contaminated soils. [ABSTRACT FROM AUTHOR]