Investigating Zn Chemical Forms in Calcareous Soils under Cultivation of Pomegranate and Almonds

Zinc (Zn) is one of the most important nutrient elements for plants, but its availability in calcareous soils is low. The availability of Zn for plants depends on relative distribution of its chemical forms in the soil, which is dependent on soil properties. The present research was conducted to investigate the distribution of chemical forms of Zn in two soils under almond and pomegranate trees using sequential extraction procedure. Results showed that the amount of DTPA extractable Zn in the surface soil under-canopy, surface soil-interspaces, subsurface soil under-canopy, and subsurface soil-interspaces were higher for almond cultivation compared to pomegranate by 12.10%, 9.91%, 19.20%, and 21.67%, respectively. The amount of available Zn on the surface soil under-canopy was higher compared to the interspaces of pomegranate trees by 9.71% and in subsoil under-canopy was higher in comparison with interspaces by 10.18%. The results showed that residual form was the highest chemical fraction of Zn followed by the Zn associated with iron oxides forms which are not available to trees. Generally, the amounts of the chemical forms of Zn were as follows: Soluble+exchangeable < organic-bound