Enriching Rice Grain Zinc through Zinc Fertilization and Water Management

Increasing rice (Oryza sativa) grain-Zn concentration is important for achieving improved human nutrition. Our objective was to understand how agronomic management practices, including water management and fertilizer-Zn application rate and timing, affect plant growth, grain-Zn concentration, and yield of rice genotypes. In a series of four-field experiments over three seasons, we tested multiple combinations of water management techniques and fertilizer-Zn application techniques. The use of alternate wetting and drying (AWD) water management increased (p < 0.001) soil redox potential and diethylene triamine pentaacetic acid (DTPA)-extractable soil Zn compared with continuous flooding (CF) in the 0- to 2-cm soil depth, but not always in the 2- to 10-cm depth. On average, AWD grain-Zn concentration increased 9% over CF without any yield penalty. Fertilizer-Zn application increased DTPA-extractable Zn only in the top soil layer and only temporarily, with a corresponding increase in grain-Zn concentration only at rates > 10 kg Zn ha(-1). Different timings of fertilizer-Zn application (from basal to flowering) had no effect on grain-Zn concentration or yield. Overall, our results indicated that AWD had a consistent and larger positive effect than fertilizer-Zn application on grain-Zn concentration. However, the increase in grain-Zn concentration due to fertilizer-Zn or water management was small, up to 2 mg Zn kg(-1) brown rice, implying that improved agronomic management alone is not sufficient to meet the target increase of at least 10 mg Zn kg(-1), but is a useful complementary strategy for enhancing the performance of Zn-enriched rice by improving soil-Zn availability.