Influence of different rates of nitrogen on fruit quality, yield and photosynthesis of 'Fuji' apple

The influence of various rates of ground-applied nitrogen (N) on yield, fruit quality, leaf photosynthesis, and leaf mineral concentrations in 'BC-2 Fuji' apple (Malus domestica Borkh.) trees was studied over several growing seasons. 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 somewhere between 31.8 and 99.8 g/tree. Considering yield and fruit quality attributes (color, firmness, fruit size, and soluble solid concentrations), optimum leaf N should be between about 2.00% to 2.10 % dwt (preferably 2.05% dwt) during an ''off-year'' or light-crop-year and between about 2.22% to 2.38% dwt (preferably 2.30% dwt) during an ''on-year'' or heavy-crop-year for production of high quality 'Fuji' fruit. In general, 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 photosynthesis decreased between mid-June and mid-August. Trees receiving 31.8 g N/tree/year had lower leaf photosynthesis than those receiving higher rates of N.