Zinc Desorption Kinetics in Corn Rhizosphere during Cultivation Period in a Calcareous Soil

Desorption of Zinc (Zn) in the rhizosphere soil is the primary factor that affects bioavailability of Zn. Desorption kinetics in the rhizosphere soil is an important process that controls the availability of the metals to plants. To investigate the effect of root activity on Zn desorption in a polluted soil at different harvesting times, a greenhouse experiment was conducted using rhizobox.

Soil sample was collected from the 0–30 cm depth of a calcareous soil from agricultural fields located in the Zanjan province, Iran. In order to study the effect of maize root exudates on the Zn desorption using from a rhizobox. The dimension of the rhizobox was 200 mm × 200 mm × 150 mm (length × width × height). The rhizobox was divided into three sections from central to left or right boundary of rhizobox which were surrounded by nylon cloth (300 mesh), viz. a central zone for plant growth (20 mm in width), near rhizosphere zones (20 mm in width), and bulk soil zones (40 mm in width). Eight seeds were sown per rhizosphere zone and subsequently thinned to two plants. Plants were grown under greenhouse conditions. Plants were harvested 30, 60 and 90 days after germination. This research was conducted in a factorial design, with 3 replications, three levels of time (30, 60 and 90 day) and three zones classified based on their distance from root. The kinetics of Zn desorption in bulk and rhizosphere soil was determined by successive extraction with DTPA-TEA in a period of 1 to 528 h at 25±1 0C.

The results showed that cumulative desorption of Zn increased with time. Zinc desorption rate in the maize rhizosphere soils were significantly (p<0.05) lower than bulk soils at 60 days after planted. There were also significant differences between harvesting times. The mean of Zn desorption in the bulk, near root and the rhizosphere soils were 278.5, 269.18 and 259.7 mg kg-1, respectively at 60 days after planted. Comparisons of R2 and SE values indicated that the power function and first-order kinetic equations described the reaction rates fairy well, as evidenced by the high coefficients of determination and low standard error of the estimate. The desorption rate constants in the first-order and power function equations have been introduced as an index of Zn desorption rates in the rhizosphere and the bulk soils. Also, the parameter b in power function was

The results of this research revealed that Zn desorption characteristics that are helpful to estimate the Zn supplying power of soils in the maize rhizosphere, are quite different in rhizosphere and bulk soil.