Liming increases yield and reduces grain cadmium concentration in rice paddies: a meta-analysis

Background and aims In China and several other rice growing countries, lime application is a common practice to alleviate soil acidification in rice paddies. Liming may also reduce the concentration of the common toxin Cadmium (Cd) in rice plants. We evaluated to what extent lime application affects rice yield and grain Cd concentration. Methods We conducted a meta-analysis to quantify the effect of liming on rice yield and grain Cd concentration, synthesizing data from 35 studies. Results Averaged across our dataset, lime application significantly increased rice yield (+ 12.9%) and soil pH (+ 0.85 units), and reduced grain Cd concentrations (-48%). Overall, grain Cd uptake and soil available Cd were reduced by 48% and 44% under liming, respectively. Liming increased rice yield more strongly 1) in soils with initial pH < 4.5 than in soils with pH >= 4.5, and 2) at lime rates >= 3.0 t ha(-1) than at lime rates < 3.0 t ha(-1). Liming-induced reductions in grain Cd concentration, grain Cd uptake and soil available Cd all increased with lime application rates. Lime application rates exceeding 1.0 and 6.0 t ha(-1) reduced average grain Cd concentrations to meet food safety standards set by the FAO/WHO and China, respectively. Conclusions Lime application is effective in both enhancing grain yield and reducing grain Cd concentrations in acidic rice paddies.