Binding forms and availability of Cd and Cr in paddy soil under non-flooding controlled irrigation

Abstract

To quantify the change in the binding forms and the availability of heavy metals Cd and Cr in paddy soil under non-flooding controlled irrigation (NFI), field experiments were conducted with flooding irrigation (FI) as control. The multi-wetting–drying condition in NFI fields enhanced the transformation of Cd and Cr in surface soil from oxidizable (B3) to acid-soluble (B1) form, and inhibited the transformation of Cd and Cr from reducible (B2) to B1 form. The B1 form Cd in NFI soil was lower, but B1 form Cr was higher than in FI soil. Thus, B3 form may play a more important role in determining the solubility of Cr than B2 in paddy soil, but it is just reverse for the metal of Cd. As a result, NFI led to higher crop uptake of Cd and Cr, but lower Cd and Cr content in the 0–20-cm surface soil and less accumulation of Cd and Cr in 40–60-cm deep soil compared with FI. It indicates that NFI results in higher bioavailability and crop uptakes, and may led to high risks in food safety in short period. But in long term, NFI will result in lower accumulation of Cd and Cr in soils, and should eventually lower the crop uptakes of Cd and Cr.