Principles and practices of foliar nutrients with an emphasis on nitrogen and calcium sprays in apple

Abstract

Foliar fertilization is a common practice to supply crops with mineral nutrients, especially under limited soil nutrient availability conditions. However, foliar-applied nutrients have to overcome the barrier properties of leaf surface to be absorbed by plants. Various pathways are reported to explain the penetration of foliar nutrients through the leaf tissues. Meanwhile, we believe that air humidity is one of the main controlling factors in this process since it controls both the actual nutrient concentration on the leaf surface as the driving force of absorption and the permeability of the leaf surface. Postharvest and prebloom foliar nitrogen sprays are applied to enhance flower bud vigor, and calcium (Ca) is applied directly to fruit during the growing season to reduce fruit susceptibility to physiological disorders. Micronutrients typically are applied in foliar sprays to uniformly distribute the small quantities of these required nutrients. In this report, we focus on the principles of foliar nutrient uptake and impacts of foliar urea and Ca sprays on fruit quality attributes of 'Fuji' apples (Malus domestica). Based on our studies, a ground application of urea is critical for a higher production of 'Fuji' apple.