Determination of zinc chemical forms in management of calcareous soils under soybean cultivation in Fars province

A sequential extraction technique for determination of soil zinc (Zn) chemical species was applied for better understanding of its mobility and availability to plants. This experiment was conducted using 10 calcareous soils with different chemical and physical characteristics from Fars province. The method presented by Singh et al. (1988) was used to determine the Zn chemical fractions. The results revealed that about 8, 2.9, 2.4 and 0.3% of the soil total Zn was present in the form of crystalline Fe-oxid-bound (CFeox), amorphous Fe-oxide-bound (AFeox), carbonates-bound (Car) and organically bound (OM) fractions, respectively. The majority of soil Zn was in the residual fraction (86.4%). Exchangeable (Ex) and Mn-oxide-bound (Mnox) species of soil Zn were not detectable. Zn associated with AFeox, residual and total Zn were negatively correlated with calcium carbonate equivalent. Zn in the AFeox fraction was positively correlated with cation exchange capacity (CEC) and clay content. There was a negative correlation between the concentration and uptake of Zn in soybean and soil CEC and clay content. The concentreations of DTPA and EDTA extractable Zn were positively correlated with Zn associated with soil carbonates. In addition, carbonates-bound Zn fraction showed a significant, positive correlation with the Zn uptake of soybean. Therefore, proper management with affection on physical and chemical properties of agricultural soils, had been great impact on bioavailability, distribution of chemical forms, uptake and concentration of Zinc on Soybean.