Effects of Zinc and Organic Fertilizer Amendments, Applied Individually or in Combination, on Cadmium Uptake by Wheat Grown in Alkaline Soil

Zinc (Zn) and organic fertilizer (OF) play a dual role in both promoting plant growth and modulating cadmium (Cd) uptake. However, the individual and combined effects of soil-applied Zn and OF on Cd accumulation in wheat remain insufficiently understood, with reported outcomes varying from inhibition to promotion of Cd uptake. Therefore, this study systematically investigated the effect of Zn, organic fertilizer, and their combined treatment on the uptake dynamics of Cd and Zn in wheat plants across different growth stages. The pot culture experiments demonstrated that applying 20 mg/kg ZnSO4 alone significantly reduced grain Cd content by 22.3% at the mature stage. Increasing the Zn dose to 40 mg/kg further enhanced the reduction, lowering Cd accumulation by 38.9% and decreasing Cd levels from 0.23 to 0.14 mg/kg. The application of 1% OF in alkaline soil enhanced soil Cd availability but did not significantly affect Cd accumulation in various wheat organs. The combination of Zn and organic fertilizer resulted in a relatively modest grain Cd reduction of 8.4–23.0%. Generally, Zn application alone was more effective in reducing Cd accumulation in wheat, while organic fertilizer may require careful use due to its Cd-mobilizing effect in alkaline soil. The combination of Zn and organic fertilizer showed limited benefits for Cd mitigation.