Multi-site Field Trials of Low-Dose Topdressing to Mitigate Cd Accumulation in Rice (Oryza sativa L.): Comparison of Different Forms of Manganese Fertilizer

Cadmium (Cd) contamination in rice is a global concern. Manganese (Mn) fertilizer is considered to be a compelling and practical agronomic measure to prevent Cd accumulation in grains. However, high doses of Mn are also toxic, while the effect of different forms of Mn fertilizer on reducing Cd absorption in rice remains unclear. To investigate the effects of low doses (37.5 kg/ha) of different Mn fertilizers (MnCl₂, MnCO₃, MnSO₄, respectively) applied as topdressing fertilizers in combination with alkaline fertilizers on reducing Cd accumulation in rice grown in typical acid Cd-contaminated paddy soil, field experiments were conducted. The findings indicate that the application of MnSO₄ led to a significant increase in soil pH by 0.18–0.27 units and a considerable decrease in CaCl₂-extractable Cd content in the soil, ranging from 37.01 to 31.88%. Moreover, the inclusion of MnSO₄ significantly increased the soil Toxicity Characteristic Leaching Procedure-Extractable Manganese (TCLP-Mn) content by 1.75–1.86 times, thereby promoting the antagonistic interactions between Cd and Mn ions in the rice rhizosphere. Furthermore, it substantially reduced Cd accumulation in rice grains by 6.47–14.00%. Utilizing structural equation modelling (SEM) revealed that soil pH and TCLP-Mn were identified as the major factors inhibiting Cd accumulation in grains, and there exists a direct significant positive effect of soil available Cd on the Cd concentration found within grains. Collectively, the findings suggest that applying low-dose Mn fertilizer, especially MnSO_4, as a topdressing combined with alkaline fertilizers is an economical and promising strategy for remediation of Cd contaminated paddy soil.

Graphical Abstract