Zinc in soil was mostly presents in different forms, including residual, oxidable, reducible and exchangeable. Generally, under submerged or flooding condition, redox potential was low, zinc in soil was more easily to be precipitated as zinc sulphide, zinc carbonate or zinc oxy-hydroxides (Kirk, 2004; Rehman et al., 2012; Impa and Johnson-Beebout, 2012). Recently, we measured the zinc in a non-flooding irrigated paddy soil, and we found the exchangeable form of Zn in was increased and Zn in oxidable form (bounded to sulfurs or organic matter) was decreased. Thus, non-flooding irrigation management led to high extractability, solubility and bioavailability of Zn in top surface paddy soil. Because there were less reductants and more dissolved organic matter in NFI soil.  

Hi Aabid,

Zn availability depends also on Fe redox cycle due to its high affinity for Fe oxides. As Fe is easiliy reduced/oxidized in flooded soils Zn availability would depend on the capacity of Fe oxides to adsorb or occlude Zn.

Dear Aabid,

Actually, there are some factors affecting Zn deficiency in Paddy fields located in arid regions among which alkaline soil pH, high CaCO3 concentration, and low organic matter content can be mentioned. In general, over application of phosphorus fertilizers that are containing high Cd Content tend to an increased amount of Cd in paddy fields which itself increases the Cd concentration in soil solution and due to existence of an antagonistic relationship  between Zn and Cd causes higher absorption of Cd by roots.  

The reason is very simple. Unlike other micronutrients, Zn is not a redox active element thus it does not readily reacts. Under submurged conditions Fe is reduced from its insoluble form Fe(III) to more soluble Fe2+ and is readily available while Zn does not.