Factors influencing the effectiveness of liming on cadmium reduction in rice: A meta-analysis and decision tree analysis.

Lime is widely applied as a soil amendment to reduce the grain cadmium (Cd) content in rice production. However, the effectiveness of liming on grain Cd reduction is inconsistent and often cannot meet the safety requirements established for rice production. To identify the factors causing the effectiveness of liming to vary, we collected data from peer-viewed articles regarding lime application in paddy soils that were published during the last ten years. The average Cd reduction rates in rice grains after liming were -44% across all the studies considered, which could be broken down into -48% for pot experiments only and -42% for field trials only. The results of a meta-analysis and decision tree analysis indicated that the experiment type (field or pot), lime dosage, lime type (CaCO3, Ca(OH)2, or CaO), soil environment factors (soil pH, soil available Cd content, soil total Cd, and Zn content), and rice cultivar all influenced the effectiveness of liming. Recommendations were made to guide future liming practice, e.g., (1) using a larger lime dosage when applied to soil with pH < 5.5, or soil with total Cd > 1 mg/kg or total Zn > 200 mg/kg; (2) using CaCO3 when applied with large dosages; and (3) planting low-Cd accumulation rice cultivars while applying lime. CAPSULE: A meta-analysis showed that the effectiveness of liming on rice grain Cd reduction was affected by the experiment type (field or pot), lime dosage, lime type, soil pH, rice cultivar, and soil total Cd and Zn content.