Effects of Nitrogen Fertilizer Management on Cadmium Concentration in Brown Rice

The technology for reducing cadmium (Cd) contamination in rice is being explored globally. In this study, the ratios of nitrogen fertilizers used were 5:5:0:0 (T1), 4:4:2:0 (T2), 6:0:2:2 (T3), and 3:2:2:3 (T4). The objective of the pot experiment was to understand how nitrogen management can reduce Cd accumulation in rice by influencing soil pH, the bioavailability of Cd concentrations in soil, Cd adsorption by iron membranes on rice roots, and the transport of mineral elements. The results indicated that nitrogen fertilizer application acidifies the soil and increases the bioavailable Cd concentration. A correlation analysis revealed a significant positive correlation between Cd concentration in the Fe plaque on rice roots and Cd concentration in the roots. Overall, the application of nitrogen fertilizers increased the concentrations of Cd and mineral elements in rice tissues, particularly in Cu, Mn, and Zn, but reduced the transfer of Cd between tissues. After nitrogen application, the concentrations of mineral elements in brown rice significantly increased, with negative correlations being observed between the Cu, Mn, and Zn concentrations and Cd concentration in brown rice. The brown rice with a nitrogen fertilizer proportion of 6:0:2:2 exhibited the lowest Cd concentration, showing significant reductions of 48.04% (X13H) and 43.46% (YZX) compared to the control treatment. These findings suggest that nitrogen management can enhance the coefficients of mineral element uptake in rice, compete against the transport of Cd to the grains, and that late-growth-stage nitrogen application can be more effective in reducing Cd concentration in brown rice.