Copper release kinetics: Effect of two extractants and wheat (Triticum aestivum L.) rhizosphere

Abstract

The greenhouse experiment was performed to determine Cu release characteristics in the bulk and the rhizosphere of some calcareous soils using rhizobox. The kinetics of Cu release in the bulk and the rhizosphere soils were determined by successive extraction with diethylenetriaminepentaacetic acid-triethanolamine (DTPA-TEA) and 10 mmol/L citric acid in a period of 1 to 504 h at 25 ± 1°C. The results of kinetics study showed that Cu extracted using DTPA-TEA in the rhizosphere soils was significantly (P < 0.01) lower than the bulk soils, while Cu extracted using citric acid in the rhizosphere soils was significantly (P < 0.01) higher than the bulk soils. The mean of released Cu after 504 h using DTPA-TEA were 8.59 and 7.46 mg/kg in the bulk and the rhizosphere soils, respectively. The mean release of Cu after 504 h using citric acid was 14.73 and 16.05 mg/kg in the bulk and the rhizosphere soils, respectively. Release kinetics of Cu in two extractants conformed fairly well to parabolic diffusion, power function, and first order equations. The results of correlation analysis illustrated that a significant correlation between Cu desorption after 504 h with citric acid and Cu concentration in wheat was found (r = 0.96 and r = 0.90 in the rhizosphere and the bulk soils, respectively, P < 0.01). Therefore, application of 10 mmol/L citric acid extractant would be recommended in the future study on the kinetics of release of Cu in calcareous soils.