The Effects of Salinity on Extractability and Chemical Fractions of Zinc in Selected Calcareous Soils of Iran

Abstract

Use of saline water for irrigation has shown considerable promise. However, its effect on the solubility and bioavailability of native soil nutrients is not well understood. This study was conducted to evaluate the effects of salinity on the behavior of zinc(Zn) in calcareous soils. The soil samples with different physiochemical properties were collected from four locations in Khorasan province (Iran). The factorial experiment was carried out as a completely randomized design on soils with four levels of water salinity (0, 37.5, 75 and 150 mole m-3 prepared with the same equivalents of NaCl and CaCl2) and four reaction times (0, 10, 20, and 30 days) with three replications. DTPA-extractable Zn was measured in the incubated soil samples after the given reaction times. Different chemical forms of Zn were characterized after 30 days using the sequential extraction procedure. DTPA-extractable Zn increased by 1 to 6.3% with the increasing levels of salinity, and decreased from 8.7 to 3.9% by increasing the reaction time significantly (P<0.05). The determination of Zn compounds by the sequential extraction procedure revealed significantly different forms of Zn with the average amounts in the following order: (KNO3+H2O)-Zn(soluble+exchangeable forms) < NaOH-Zn(organic form) < EDTA-Zn (carbonate form) << HNO3 -Zn (residual). Salinity affected various forms of Zn i.e. soluble + exchangeable, organic and residual. Increasing soil salinity level increased the KNO3+H2O extractable Zn by 20 to 80% and the NaOH extractable form by 8.6 to 43%. DTPA-Zn was significantly correlated with the NaOH extractable form (r=0.98 P<0.05) and with the (KNO3+H2O)-Zn, (r=0.94 P<0.05). It was concluded that increasing salinity redistributed HNO3-extracted Zn (residual) to the KNO3+H2O extractable (soluble + exchangeable) and NaOH extractable (organic) forms of Zn.