Increasing soil moisture faciliates the outcomes of exogenous sulfate rather than element sulfur in reducing cadmium accumulation in rice (Oryza sativa L.)

Cadmium (Cd) contamination in paddy soils and the related pollution risk of rice grain have received increasing attention. Agronomic measures, such as the application of sulfur and changes in water regimes, were reported to mitigate the accumulation of Cd in rice. However, there is limited information on the combined effects of sulfur application and water regimes. Therefore, a pot experiment was conducted to investigate the effects of two sulfur forms, three water regimes and multiple sulfur application rates on Cd accumulation in rice. The sulfur was applied as SO42− (SVI, replacing the traditional fertilizers by SO42--containing fertilizers), and element S (S0) was applied at 0, 10, 20, 30 and 40 mg S kg−1 soil. The water regimes were continuous flooding (F), flooding-moist alternation (FM), and moist irrigation (M), for a total of 30 treatments. The results indicated that application of SVI exceeding 30 mg S kg−1 significantly reduced the Cd concentrations in brown rice by 31.1–56.3%, and the Cd concentrations decreased with increasing amount of irrigation water. Similar reductions in Cd concentrations in rice shoots and rice straw collected at tillering and maturity stages were observed after application of SVI. However, the effect of S0 application on Cd accumulation in grain was not significant under different water regimes. Furthermore, this study found that application of both SVI and S0 inhibited the transfer of Cd from rice roots to shoots in most cases. These findings indicate that replacing traditional fertilizers with SO42--containing fertilizers, especially combined with increased irrigation, could be a potential approach to mitigate Cd accumulation in rice growing in Cd-contaminated acidic paddy soils. [Display omitted] •The effect of sulfur supply on the accumulation of Cd in rice under different water regimes was tested.•Reduction effect of SVI on rice grain Cd enhanced as irrigation water increased.•Application of S0 has a limited effect on the accumulation of Cd in rice.•Both forms of sulfur inhibited Cd transfer from roots to shoots in most cases.