Grain zinc and yield responses of two rice varieties to zinc biofortification and water management

Zinc (Zn) biofortification can improve grain yield and nutritional quality in rice, but its effectiveness is subject to agronomic practices and other factors. In a previous study, the application of Zn to soil enhanced grain Zn in lowland rice in well-drained and waterlogged soil, whereas grain Zn in upland rice increased only in well-drained soil. This new study explores the hypothesis that the application of foliar Zn can enhance grain Zn in upland and lowland rice grown under waterlogged and well-drained conditions. Two rice varieties, CNT1 (wetland rice) and KH CMU (upland rice) were grown in containers in waterlogged or well-drained soil with three Zn treatments (no Zn, soil Zn and foliar Zn). For the soil Zn treatment, 50 kg ZnSO4 ha−1 was applied to the soil before transplanting. For the foliar treatment, 0.5% ZnSO4 (equivalent to 900 L ha−1) was applied at booting and repeated at flowering and milky growth stages. Grain yield in CNT1 was 15.9% higher in the waterlogged than in the well-drained plants, but the water regime had no effect on grain yield in KH CMU. Grain Zn concentration in CNT1 increased from 19.5% to 32.6% above the no Zn control when plants were applied with soil or foliar Zn. In KH CMU, there was an interaction between the water regime and Zn treatment. Application of foliar Zn increased grain Zn by 44.6% in well-drained and 14.7% in waterlogged soil. The results indicate strong interaction effects between variety, water regime and Zn fertilizer application on Zn biofortification in rice. Thus, the selection of rice varieties and growing conditions should be considered in order for producers to achieve desirable outcomes from high grain Zn concentrations

Foliar zinc application improved grain zinc accumulation and bioavailable zinc in unpolished and polished rice

This study examined the effect of foliar zinc (Zn) application on grain yield, Zn and phytate concentrations and its impact on the phytate:Zn molar ratio, an indicator for Zn bioavailability in human digestive tracts, in unpolished and polished rice between two rice cultivars across two cropping years. The modern improved rice cultivar CNT1 and the traditional improved cultivar KDK were foliar applied with five rates of ZnSO4 in two cropping years. In 2016, 0.3% ZnSO4 increased the Zn concentration of unpolished rice in KDK by 21% over the nil Zn, while the effect was not found in CNT1. In polished rice, 0.2–0.4% ZnSO4 increased the Zn concentration by 11.2–20.0% in CNT1 and by 8.3–24.1% in KDK, and decreased the phytate concentration by 5.2–16.9% in KDK but not in CNT1. In 2017, 0.4% ZnSO4 increased the Zn concentration by 18.2–26.2% and 32.4–42.6% in unpolished and polished rice, respectively, in both cultivars. Application of 0.4% ZnSO4 decreased the phytate:Zn molar ratio in polished rice from 29.7 to 18.3 and from 26.4 to 17.9 in CNT1 and KDK, respectively in 2016, and from 15.7 to 12.6 in KDK in 2017. Foliar Zn application decreased the phytate:Zn molar ratio in unpolished rice from 27.9 to 22.7 and from 21.9 to 17.2 in CNT1 and KDK, respectively in 2017, but had no effect in 2016. Thus, foliar Zn application can improve grain Zn concentration and decrease the phytate:Zn molar ratio in both unpolished and polished rice but the response can vary with cropping year and cultivar