LIGHT-DISTRIBUTION IN APPLE ORCHARD SYSTEMS IN RELATION TO PRODUCTION AND FRUIT-QUALITY

The effect of tree density (2000, 2667, and 4000 trees per ha) and the ratio of between to within-row distance (1:1, 2:1, and 3:1) on light interception, fruit production, colour and individual fruit weight was evaluated in a ten-year comparative field study with apple at two sites in The Netherlands (51 degrees 30' and 52 degrees 0' N) and one site in Denmark (55 degrees 30'). For each combination of tree density and rectangularity, trees were pruned at three heights (1.50, 1.88, or 2.25 m). Fruit production over nine years and seasonal incoming radiation between bloom and harvest were 20 and 15% greater in The Netherlands. Climate-based estimates of potential production as provided by a crop-growth model, predicted 18% higher fruit production in The Netherlands. Production was proportional to light interception and increased with tree density, but the amount of well-coloured fruit per ha in later years did not increase with planting density. With more than 70% tight interception in later years, a large proportion of shade within the canopy was found. Fruits were smaller and less coloured at the Danish site. Fruits were more coloured in the taller and more open trees, even at the highest tree densities. Plantings with 1:3. and 2:1 between-to within-row distances intercepted more light and had a more uniform light distribution than 3:1 designs. This led to higher fruit production and better fruit colour. Fruit weight was not influenced by tree density, rectangularity, or tree height.