Preharvest iodine sprays at high rates are more effective in biofortification of apples than soil application

Abstract

Abstract Aim Agronomic biofortification of fruit with iodine (I) has become an innovative approach in contemporary agriculture. In this study, we evaluated the influence of soil- and foliar I applications on absorption of this nutrient by apple (Malus domestica Borth.) trees, as well as on growth and yield responses of the plants. Methods In 2018–2019, ‘Red Jonaprince’ apple trees, grown on sandy loam soil, were treated with potassium iodide (KI) or K-iodate (KIO3) through soil application (at a rate of 4 kg, 8 kg or 12 kg I ha−1) or preharvest sprays (at a rate of 0.5 kg, 1 kg or 1.5 kg I ha−1). Results The I sprays increased apple I contents to the targeted range of 50–100 µg 100 g−1 fresh weight and even to the recommended daily intake of I for adults (the KI sprays at rates of 1 kg and 1.5 kg I ha−1). Although the I sprays caused leaf injuries, they did not affect tree growth and yield. However, the spray of KI and KIO3 at the highest rate decreased the soluble solid concentration in fruit. For soil-supplied trees with I, an increase in apple I concentration was found only in the first year of the study. Conclusions Apple tree is a suitable target plant for agronomic I biofortification, and from the economic point of view, the spray of KI or KIO3 at a rate of 0.5 kg I ha−1 should be recommended in orchards.