Alternate Wetting and Drying Irrigation and the Bioaccumulation of Selected Micronutrients in Harvested Rice Grains.

Alternate wetting and drying irrigation (AWDI) is a water saving strategy in rice farming. However, its impact on mineral bioaccumulation in the grain is not well understood. Thus, this study investigated the impact of AWDI on bioaccumulation of Zn, Se, Mn and Cu in rice grains. Six water regimes involving continuous flooding where water was maintained at 2cm above the soil, and delaying irrigation until water reaches 5, 10, 20, 30 and 40cm below the soil surface, were employed. The concentration of Zn, Mn and Se in the soil ranged between 2.05–6.9, 3.4–9.1 and 0.13–0.16 mgkg-1, respectively. In the harvested rice grains, the concentration of Zn, Mn, Cu and Se ranged between 8.20–11.90, 1.90– 3.50, 1.90–3.10 and 0.10–0.70 mgkg-1, respectively. These concentrations were not phytotoxic to plants. Re-flooding after every 2–5 days increased Zn, Mn and Cu bioaccumulation in rice grains by 65, 151 and 124% respectively, but reduced Se bioaccumulation by 95%. Re-flooding after every 8–12 days reduced bioaccumulation of all micronutrients in rice grains. Bioaccumulation factors indicated that Zn was absorbed and subsequently accumulated in rice grains. The estimated dietary daily intakes for Zn, Mn and Cu were higher in rice grown under mild AWDI, implying that AWDI can be used as a strategy to increase these micronutrients in human diets through rice consumption. [ABSTRACT FROM AUTHOR]