Effect of wheat (Triticum aestivum L.) rhizosphere and sewage sludge application on zinc desorption with dilute citric acid

Abstract

Rhizosphere processes have a major impact on Zn desorption and Zn uptake by plant. However, information about Zn desorption characteristics in the rhizosphere of wheat is limited. Therefore, a greenhouse experiment was performed to determine Zn desorption characteristics in the bulk and rhizosphere soil of wheat (Triticum aestivum L.) of 10 soils amended and un-amended with municipal sewage sludge using rhizoboxes. The kinetics of Zn desorption was determined by successive extraction with 10 mM citric acid in a period of 1–504 h at 25 ± 1°C in the bulk and rhizosphere of un-amended and amended soils. The results showed that the Zn amount extracted after 504 h in the rhizosphere soils was significantly (p < 0.01) higher than the bulk soils. The mean of Zn desorption in the bulk and rhizosphere of un-amended soils were 10.4 ± 0.34 and 11.4 ± 0.43 mg kg−1, respectively, while the mean of Zn desorption in the bulk and the rhizosphere of amended soils were 13.2 ± 0.48 and 14.8 ± 0.67 mg kg−1, respectively. Desorption kinetics of Zn conformed fairly well to the first-order, parabolic diffusion, power function, and zero-order equations. The results of Zn fractionation indicated that exchangeable Zn and Zn associated with organic matter decreased and Zn associated with iron-manganese oxides and residual Zn increased in the rhizosphere soils compared to the bulk soils. Zinc desorption after 504 h and residual Zn in the bulk and rhizosphere of un-amended and amended soils were significantly positively correlated (p < 0.05). Therefore, residual Zn was the main Zn pool that controlled Zn desorption after 504 h in the bulk and rhizosphere soils studied.