Foliar zinc fertilization improves yield, biofortification and nutrient-use efficiency of upland rice

Zinc (Zn) deficiency is an enormous challenge to human health, particularly where rice is the principal food as it is inherently low in bioavailable Zn. Recent research has demonstrated the worth of biofortification of food-crops, particularly in regions with low phytoavailable Zn levels in the soils, to improve the rice grain Zn concentration. We tested different Zn fertilizer management methods for leading upland (rainfed) rice genotypes of north-eastern India to assess their potential to improve Zn-use efficiency, grain biofortification and yield. Of the three tested genotypes, the Bhalum-3 achieved 15.7–25% higher grain yield and 15.3–30.5% higher partial factor productivity over the Bhalum-1 and Bhalum-5 varieties, respectively. All three rice genotypes achieved statistically similar rice grain Zn concentrations (33.8–34.3 mg kg−1). Applying Zn as zinc sulfate foliar spray increased grain and straw yield by 16.3% and 18.8% respectively, relative to the control treatment. Applying Zn fertilizer (either as a foliar spray or into soil) increased grain Zn concentration relative to that of the control treatment; maximum biofortification was achieved with foliar application (37.9 mg kg−1), where the Zn concentration in grains was 29% higher than the control. Furthermore, the highest hulling (79%), milling (67.9%) and head rice recovery (57.6%) rates were recorded under foliar Zn application. To increase nutritional security, improve Zn biofortification and achieve higher rice yields, particularly in soils with small phytoavailable Zn pools, we recommend the use of foliar Zn fertilizers for upland rice.