Efficacy of cheap amendments for stabilizing trace elements in contaminated paddy fields

Area of Science:

• Environmental Science
• Soil Science
• Agronomy

Background:

• In situ stabilization using affordable amendments is a promising technique for large-scale soil remediation.
• Previous research has primarily focused on short-term laboratory or pot experiments, lacking field-scale validation.
• Understanding amendment effects on bioavailable metals and crop uptake is crucial for practical application.

Purpose of the Study:

• To evaluate the effectiveness of dolomitic lime, oyster shell (OS), and sugarcane bagasse compost (SC) in remediating trace element-contaminated paddy soil.
• To assess the impact of these amendments on the bioavailable concentrations of chromium (Cr), nickel (Ni), copper (Cu), and zinc (Zn).
• To determine the effect of amendments on metal uptake in rice (Oryza sativa L.) grown in field conditions.

Main Methods:

• Field application of dolomitic lime (40 ton ha⁻¹), oyster shell (OS) (80 ton ha⁻¹), and sugarcane bagasse compost (SC) (60 ton ha⁻¹) in a Taiwanese paddy field.
• Two rice cropping seasons were conducted to evaluate long-term effects.
• Analysis of 0.1 N HCl-extractable metals in soil and metal concentrations in brown rice.

Main Results:

• Both lime and OS treatments significantly reduced 0.1 N HCl-extractable Cr, Ni, Cu, and Zn in the soil, primarily due to increased soil pH.
• Oyster shell (OS) significantly reduced Cu, Zn, and Ni concentrations in brown rice.
• Sugarcane bagasse compost (SC) was not effective and decreased soil pH, potentially increasing metal bioavailability.

Conclusions:

• Oyster shell (OS) is a cost-effective, locally available, and environmentally compatible amendment for field-scale remediation of metal-contaminated soils.
• Increased soil pH is the main mechanism for metal immobilization by lime and OS.
• Sugarcane bagasse compost (SC) is not recommended for immobilizing these trace elements due to its adverse effect on soil pH.