Liming and tillering application of manganese alleviates iron manganese plaque reduction and cadmium accumulation in rice (Oryza sativa L.)

Highlights: • Basal Mn alone induced higher Mn and lower Cd levels in rice than later application. • Soil liming inhibited iron manganese plaque and enhanced Cd transport in rice. • Tillering Mn greatly alleviated liming effects on Mn plaque and Cd transport. • Liming coupled with tillering Mn caused the highest reduction in brown rice Cd. The application time and soil pH are key to manganese (Mn) bioavailability, which may influence Mn effects on cadmium (Cd) accumulation in rice. Accordingly, this study investigated the effects of Mn application at different stages, alone or with basal liming, on Cd accumulation in rice through pot and field experiments. The results showed that basal Mn application maximally elevated soil dissolved Mn, and increasing Mn accumulation in rice by 140%−367% compared to the control. Additionally, basal or tillering applications had better effects on enhancing iron manganese plaque (IMP) and inhibiting CaCl₂-extractable Cd than later applications. Therefore, basal and tillering Mn reduced brown rice Cd by 24.6% and 18.9% compared to the control, respectively. Liming reduced CaCl₂-extractable Cd by 83.3% compared to the control but inhibited soil dissolved Mn (25.8%−76.6%) and IMP (28.9%−29.7%), resulting in only a 41.7% reduction in brown rice Cd. Liming combined with tillering Mn maximally reduced brown rice Cd by 67.4%, structural equation modeling revealed CaCl₂-extractable Cd and manganese plaque played the greatest positive and negative roles, respectively. Therefore, basal liming and tillering application of Mn is most effective at reducing rice Cd through inhibition of Cd bioavailability and alleviation of IMP reduction.