Effects of long-term fertilization practices on heavy metal cadmium accumulation in the surface soil and rice plants of double-cropping rice system in Southern China

Fertilizer regime is playing an important role in heavy metal cadmium (Cd) accumulation in paddy soils and crop plant. It is necessary to assess the Cd accumulation in soils and rice (Oryza sativa L.) plants under long-term fertilization managements, and the results which help to assess the environmental and food risk in Southern China. However, the effects of different organic manure and chemical fertilizers on Cd accumulation in soils and rice plant remain unclear under intensively cultivated rice conditions. Therefore, the objective was to explore Cd accumulation in paddy soils and rice plant at mature stage under different long-term fertilization managements in the double-cropping rice system. Cd accumulation in the surface soils (0–20 cm) and rice plant with chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), 30% organic matter and 70% chemical fertilizer (LOM), 60% organic matter and 40% chemical fertilizer (HOM), and without fertilizer input (CK) basis on 32 years long-term fertilization experiment were analyzed. The results showed that the soil total Cd content was increased by 0.296 and 0.351 mg kg⁻¹ and 0.261 and 0.340 mg kg⁻¹ under LOM and HOM treatments at early and late rice mature stages, respectively, compared with the CK treatment. And the soil available Cd content was increased by 0.073 and 0.137 mg kg⁻¹ and 0.102 and 0.160 mg kg⁻¹ under LOM and HOM treatments at early and late rice mature stages, respectively, compared with the CK treatment. The bioconcentration factor of Cd across different parts of rice plant was the highest in root, followed by stem and grain, and the lowest in leaves. At early and late rice mature stages, the root Cd concentration of rice plant was increased by 0.689 and 0.608 mg kg⁻¹ with HOM treatment, the stem Cd concentration of rice plant was increased by 0.666 and 0.758 mg kg⁻¹ with RF treatment, and the leaf and grain Cd concentration of rice plant was increased 0.094 and 0.082 mg kg⁻¹ and 0.086 and 0.083 mg kg⁻¹ with LOM treatment, respectively, compared with the CK treatment. The soil Cd single-factor contaminant index (PCd) under different fertilization treatments was as the following HOM > LOM > RF > MF > CK. Meanwhile, the PCd with LOM and HOM treatments was higher than that of the MF, RF, and CK treatments, but there is no significant difference between that of MF and RF treatments. Therefore, long-term application of rice straw residue and chemical fertilizer had no obvious effect on the accumulation of Cd in paddy soils and grain, and soil Cd accumulation was increased as application of organic fertilizer.