Zinc Availability and Dynamics in the Transition from Flooded to Aerobic Rice Cultivation

Zinc (Zn) deficiency is a fairly wide spread agronomic constraint in many of the world rice production regions. Zn deficiency inhibits several plant biological and physiological processes including carbohydrate metabolism, maintenance of cell turgidity and protein synthesis. Water scarcity is currently necessitating a shift towards non-flooded rice cultivations, which can have substantial impact on soil Zn availability. Zn availability is a function of both plant and soil factors; these could largely be influenced by the shift in water management. For example, in aerobic rice systems, iron oxidation by root-released oxygen causes reduction in rhizosphere pH. The reduced pH limits the release of Zn from highly insoluble fractions. Redox potential often increases in the aerobic cultivation, leading to iron oxidation and concomitant acidification and precipitation of Fe (OH)3 onto which Zn may adsorb. The consequences of the transition in water management necessitate applying fertilizers to correct Zn deficiency and increase grain yield. This paper reviews Zn dynamics and availability in different rice growing systems. The review focuses on soil-plant processes which are influenced by the shift in water management. Fertilization strategies to correct Zn disorder and increase grain Zn content are also discussed.