COMPUTED EFFECTS OF SPACING ON LIGHT INTERCEPTION AND DISTRIBUTION WITHIN HEDGEROW TREES IN RELATION TO PRODUCTIVITY
Light interception only gives an indication of the potential yield of an orchard, the actual yield can be less or of small size because of serious within-tree shading. The computer model was also used to map the light distribution patterns within full-field, spindlebush and palmette orchards. Over a wide range of hedgerow dimensions and between-row spacings, a linear relationship was found between the maximum light interception achievable before serious shading occurs and the maximum light interception which would be achieved if the trees were solid (Fmax in Jackson's notation). From this it is now possible to predict the leaf area index needed in an orchard of known Tf to maximise production of top quality apples. Any further increase in leaf area will only lead to the production of small fruit, although total yield and dry-matter production will increase with the increase in light interception.