Sowing date optimization mitigates cadmium accumulation in rice‐ratoon rice cropping systems

BACKGROUND Cadmium (Cd) contamination in rice has become a global issue. However, limited information exists regarding the impact of sowing dates on Cd accumulation in ratoon rice (RR) and its associated health risks. This study involved a two‐season field experiment on rice‐ratoon rice, which was conducted on a mildly Cd‐contaminated soil in southern China. Two rice genotypes were selected, and sowing was carried out from April to July, encompassing a total of eight sowing date treatments. RESULTS Compared to the main season, two sowing date treatments in the ratoon season exhibited significantly higher Cd concentrations in brown rice and their associated health risks (maximum 61.54% higher), whereas two treatments showed significantly lower levels, and no significant differences in the remaining cases. In the main season, inbred rice varieties with shorter growth periods demonstrated higher Cd levels in tissues with earlier sowing (up to 2.89 times higher), whereas hybrid rice varieties with longer growth periods exhibited a trend of initially decreasing and then increasing Cd levels with delayed sowing dates (up to 1.64 times higher). Conversely, the ratoon season showed a trend of initially increasing and then decreasing Cd levels. Structural equation modeling revealed that rainfall had a negative standardized total effect on Cd accumulation in brown rice across both seasons, whereas the integrated temperature index and illumination hours exhibited opposing positive and negative effects in the respective seasons. CONCLUSION Collectively, optimizing sowing dates based on regional climate conditions can significantly alleviate Cd accumulation in RR, minimizing associated health risks.