Optimum Ranges of Leaf Nitrogen for Yield, Fruit Quality, and Photosynthesis in ‘BC-2 Fuji’ Apple

Abstract

The influence of five rates of ground-applied nitrogen (N) on yield, fruit quality attributes (fruit size, color, firmness, soluble solid concentrations, and starch), and leaf mineral concentrations and photosynthesis in ‘BC-2 Fuji’ apple [ Malus sylvestris(L.) Mill. var. domestica(Borkh.) Mansf.] trees were studied to determine optimum ranges of leaf N for quality fruit and yield. Fruit skin red color decreased as the rate of N increased. Under the environmental conditions of this experiment, annual ground application of N for optimum fruit quality should be more than 31.8 g/tree/year but less than 99.8 g/tree/year, preferably about 65.8 g/tree/year. Optimum leaf N should be between 2.00% and 2.10% dry weight (preferably about 2.05% dry weight) in a light-crop year or an "off-year" and more than 2.22% but less than 2.38% dry weight (preferably about 2.30% dry weight) in a heavy-crop year or an "on-year" for production of high quality fruit. Leaf K decreased while leaf Mg and Mn increased with increase in N application. Fall application of N often resulted in lower leaf N, thus, better fruit color. Other fruit quality attributes were not consistently affected by time of N application. Leaf net photosynthesis (Pn) decreased between mid-Jun and mid-August. Trees receiving 31.8 g N/tree/year had lower leaf Pn than those receiving higher rates of N.