Effects of forms and rates of potassium fertilizers on cadmium uptake by two cultivars of spring wheat (Trictium aestivum, L)

Abstract

A greenhouse pot experiment was conducted to study the influence of potassium fertilizers in different forms and rates on cadmium (Cd) uptake by two cultivars of spring wheat (Triticum aestivum, L.): Brookton and Krichauff. Potassium fertilizers were added to soil at four levels: 0, 55, 110 and 166 mg K kg⁻¹ soil as KNO₃ (N), KCl (C) or K₂SO₄ (S). CdCl₂ was added to all the treatments at a uniform rate equivalent to 15 mg Cd kg⁻¹ soil. Plant shoot and root dry weights (DW) of both cultivars were reduced significantly by the addition of K-fertilizer in C and S treatments but there were only marginal changes in the N treatments. The Cd concentrations in shoots and whole plants increased significantly (P<.001) with increasing K addition, from 37.5 to 81.4 mg kg⁻¹ and from 42.9 to 86.8 mg kg⁻¹ for Brookton and Krichauff, respectively. However, no obvious effect was observed in the N treatments, except for the highest K level (K3) where there was a sharp increase in Cd concentration compared to the lower additions. Forms of K-fertilizers significantly influenced the Cd concentrations in plant shoots and roots (P<.001), but there was no significant difference between C and S treatments. This experiment showed that anions Cl⁻ and SO₄²⁻ increase Cd uptake by plants, which can be interpreted as Cl⁻ and SO₄²⁻ complexing readily with Cd²⁺ and thereby increasing the bioavailability of Cd²⁺ in soils. The effect of potassium itself on plant uptake of Cd was also observed. We suggest that when applying potassium fertilizer to Cd-contaminated soils, the forms and rates should be considered.