A field experiment was conducted in moderately and severely Cd contaminated paddy fields in Beishan Town, Changsha City, Hunan Province. This study examined the effects of LS amendment (limestone+sepiolite), in combination with soil application and foliar spraying of Zn fertilizer, on Cd uptake in early and late rice plants. The results showed that: ① the application of LS (2250 kg·hm-2 and 4500 kg·hm-2) significantly increased pH and CEC values in paddy soil during the early and late rice seasons, but the addition of Zn fertilizer (90 kg/hm2) to soil and through foliar spraying (0.2 g·L-1 and 0.4 g·L-1) had no significant effects on the pH or CEC of the soil. ② LS application decreased concentrations of TCLP-Cd and CaCl2-Cd in the soils, by 11.5%-38.8% and 24.0%-81.0%, respectively, while neither of the treatments involving the addition of Zn fertilizer to soil or through foliar spraying had any significant effects on the concentrations of TCLP-Cd and CaCl2-Cd. ③Single treatments involving only LS amendment, Zn fertilizer in soil, or foliar spraying of Zn fertilizer also reduced Cd concentrations in brown rice, but to a lesser degree than the combined treatments. The combined treatments (L1Z1F1, L1Z1F2, L2Z1F1, and L2Z1F2) reduced Cd concentrations in brown rice by 64.9%-67.5% and 56.1%-80.6%, for early and late rice, respectively, while L2Z1F1 (4500 kg·hm-2 LS+90 kg·hm-2 Zn fertilizer+foliar spraying 0.2 g·L-1 Zn fertilizer) resulted in the largest reduction in Cd concentration in brown rice. ④ The Cd/Zn ratio in brown rice was significantly positively correlated with Cd concentrations, indicating that increased Zn concentration in different rice tissues was one of the key reasons for decreased Cd concentration in brown rice. Clearly, as a remediation technology, combining LS amendments with zinc fertilizer is an effective method for achieving the safe utilization of moderately and severely Cd contaminated paddy fields, by effectively inhibiting the uptake, accumulation, and transportation of Cd in rice plants and decreasing Cd concentrations in brown rice.
Keywords: Cd contaminated soil; combined amendment; foliar resistance control; rice; zinc fertilizer.