Zinc Nutrition and Redox Relationships of Submerged Paddy Rice.

Zinc deficiency in paddy rice is a worldwide problem of increasing magnitude. The effect of redox relationships on the zinc nutrition of submerged paddy rice was studied in the greenhouse and laboratory. The result of this study indicated that frequently observed zinc deficiency in submerged paddy rice can be explained in part by the increased reduction and solubilization of iron and manganese which have an antagonistic effect on the uptake and availability of zinc. Furthermore it is hypothesized that zinc solubility in submerged soils may be depressed as iron is solubilized in reduced microsites and precipitated in more oxidized zones as Fe₃(OH)₈ (ferrosic hydroxide). Because of its higher solubility metastable ferrosic hydroxide suppresses Zn²⁺ actively through formation of a franklinite-like solid (ZnFe₂O₄). However, this hypothesis needs further testing. In this presentation both laboratory and greenhouse studies for Zinc nutrition and redox relationships of submerged paddy rice will be discussed.