Optimizing Zinc Fertilizer and Water Management for Increased Rice Grain Zinc.

Zinc is the most important micronutrient deficiency in flooded rice. Rice Zn deficiency may result in human Zn deficiency in rural Asia, making people more susceptible to diarrhea and pulmonary disease. Zinc is less available in soil at low redox potential under flooded conditions, and added Zn fertilizer may also become unavailable, resulting in low grain Zn even after fertilization. In a greenhouse experiment, a high-grain-Zn rice line (IR69428-6-1-1-3-3) was grown with Zn fertilizer applied at one of four times throughout the season, combined with one of three water treatments: continuous flooding, mid-season drainage, or late season drainage. Available soil Zn increased from 0.5 to 2 mg kg^-1 with Zn fertilizer application under continuous flooding. When Zn was added to soil during either drainage period, available Zn increased up to 35-40 mg kg^-1. Vegetative Zn uptake was greater during mid-season drainage period compared with flooded control. Grain Zn concentration was significantly higher when Zn was added during grain-filling and coinciding with late season drainage, reaching 37 mg kg^-1 in brown rice compared with 32 mg kg^-1 in the flooded control without Zn fertilization.