The Effects of Reducing Nitrogen and Increasing Density in the Main Crop on Yield and Cadmium Accumulation of Ratoon Rice

Rice cultivated in cadmium (Cd)-polluted acidic paddy soil poses important health risks in China. Mitigating Cd accumulation in rice is of crucial importance for food safety and human health. In this study, using Chuangliangyou 669 as the ratoon rice variety, a field experiment was conducted in paddy fields with severe Cd pollution (Cd concentration > 1.0 mg kg⁻¹). The aim was to explore the impacts of different nitrogen (N) fertilizer levels (N1-180 kg hm⁻², N2-153 kg hm⁻², N3-126 kg hm⁻²) and planting densities (D1-20 cm × 20 cm, D2-16.7 cm × 16.7 cm) in the main crop on the yield and Cd accumulation characteristics of ratoon rice. The results showed that reducing the amount of N fertilizer would lead to a decrease in the yield of ratoon rice, while increasing the planting density could increase the yield, mainly by increasing the effective panicle. Among the various combined treatments, the yields of N1M2 and N2M2 were relatively high. The planting density had no significant impact on the Cd concentration, translocation factor and bioaccumulation factor of ratoon rice. The Cd concentration in various tissues of ratoon rice decreased significantly with the reduction in N fertilizer application. Reducing N fertilizer application could increase the pH, reduce the concentration of available Cd in the soil and consequently reduce the Cd bioaccumulation factor of various tissues of ratoon rice and the Cd translocation factor from roots and stems to brown rice. Considering both the yield and the Cd concentration in brown rice, N2M2 was the optimal treatment of reducing N and increasing density, which could maintain a relatively high yield while significantly reducing the Cd concentration.