The influence of phosphate fertilizer application levels and cultivars on cadmium uptake by Komatsuna (Brassica rapa L. var. perviridis)

Cadmium (Cd) is a common impurity in phosphate fertilizers and application of phosphate fertilizer may contribute to soil Cd accumulation. Changes in Cd burdens to agricultural soils and the potential for plant Cd accumulation resulting from fertilizer input were investigated in this study. A field experiment was conducted on Haplaquept to investigate the influence of calcium superphosphate on extractable and total soil Cd and on growth and Cd uptake of different Komatsuna (Brassica rapa L. var. perviridis) cultivars. Four cultivars of Komatsuna were grown on the soil and harvested after 60 days. The superphosphate application increased total soil Cd from 2.51 to 2.75 mg kg ⁻¹, 0.1 mol L ⁻¹ hydrochloric acid (HCl) extractable Cd from 1.48 to 1.55 mg kg ⁻¹, 0.01 mol L ⁻¹ HCl extractable Cd from 0.043 to 0.046 mg kg ⁻¹ and water extractable Cd from 0.0057 to 0.0077 mg kg ⁻¹. Cd input reached 5.68 g ha –¹ at a rate of 240 kg ha –¹ superphosphate fertilizer application. Superphosphate affected dry-matter yield of leaves to different degrees in each cultivar. ‘Nakamachi’ produced the highest yield in 2008 and ‘Hamami No. 2’ in 2009. Compared with the control (no phosphate fertilizer), application of superphosphate at a rate of 240 kg ha –¹ increased the Cd concentration in dry leaves by 0.14 mg kg ⁻¹ in ‘Maruha’, 1.03 mg kg ⁻¹ in ‘Nakamachi’, 0.63 mg kg ⁻¹ in ‘SC8-007’ in 2008, and by 0.19 mg kg ⁻¹ in Maruha’, 0.17 mg kg ⁻¹ in ‘Hamami No. 2’, while it decreased by 0.27 mg kg ⁻¹ in ‘Nakamachi’ in 2009. Field experiments in two years demonstrated that applications of different levels of calcium superphosphate did not influence Cd concentration in soil and Komatsuna significantly. However, there was a significant difference in Cd concentration of fresh and dry Komatsuna leaves among four cultivars in 2008 and 2009. The highest Cd concentration was found in the ‘Nakamachi’ cultivar (2.14 mg kg ⁻¹ in 2008 and 1.91 mg kg ⁻¹ in 2009). The lowest Cd concentration was observed in the ‘Maruha’ cultivar (1.51 mg kg ⁻¹ dry weight (DW)) in 2008 and in the ‘Hamami No. 2’ cultivar (1.56 mg kg ⁻¹ DW) in 2009. A decreasing trend in Cd concentration was found in ‘Nakamachi’, followed by ‘SC8-007’, ‘Hamami No. 2’ and ‘Maruha’ successively. It is necessary to consider a low-uptake cultivar for growing in a Cd polluted soil. In these two years’ results, ‘Maruha’ cultivar was the lowest Cd uptake cultivar compared to the others.