Remediation of Cadmium-contaminated Rice Fields by Three Consecutive Years of Amendment Application

Objective The aims were to investigate the remediation effect of lime, biochar and silicon fertilizer on moderate Cd-contaminated rice fields after three consecutive years of application.

Method The soil and rice system of typical double-cropping rice area in Hunan Province was selected as the research object. Four treatments, control (T1), application of lime (T2), biochar (T3) and silicon fertilizer (T4), were used in conducted in a randomized group design to analyze the physicochemical properties of paddy soil and the cadmium content of rice with different amendments. The effects of soil factors on cadmium transport in soil-rice system were investigated by redundancy analysis and regression analysis.

Results The results showed that T₂ increased soil pH to 6.92 ± 0.05, soil available Cd decreased to 0.41 ± 0.09 mg kg⁻¹ compared with T_1. There were no significant differences in soil pH, available Cd and dissolved organic matter in T₃ and T₄ treatments compared with T₁ treatments. Cd content in brown rice in T₃ treatment were the highest in the early and late season at 0.54 ± 0.07 and 0.11 ± 0.04 mg kg⁻¹. The T₂ treatment had the lowest at 0.16 ± 0.00 and 0.03 ± 0.01 mg kg⁻¹. The redundancy analysis showed that Cd content in brown rice was negatively correlated with soil pH and positively correlated with soil available Cd (DPTA-Cd). The relationship between brown rice cadmium content (RiCd) and soil available Cd was as follows: RiCd mg kg⁻¹= -0.0822 + 0.297 DPTA-Cd mg kg⁻¹ (R_adj²₌0.503, P < 0.05).

Conclusion Continuous application of lime for 3-year effectively remediated paddy fields under moderately cadmium pollution due to soil pH increase and soil available cadmium reduction, could cut down the Cd content in brown rice.