Aspects of light climate within apple orchards.
The apple orchards studied had discontinuous bush-and hedge-type canopies of mean leaf-area indexes of 1-1-4. These values were low, owing to the existence of alleys between the trees; up to one-third of the ground was not covered by tree canopy. Leaf area indexes ranged from 0 in the alleys to over 3 in the tree centres, so that there was a great variation in the angular direction from which different parts of the trees received the greater part of their illumination. Light sensors responding equally to light at all angles above the horizontal were therefore used, and these showed that the light intensity in the denser parts of the trees and under tree centres was about 10% of that above the canopy. Within the main fruiting zone of the canopy light intensities ranged from 30% to 95% of full sunlight. Large and well-coloured fruits were only found under conditions of high light intensity. A more even distribution of the foliage over the orchard would have increased the volume of adequately illuminated canopy. [See ateo H.A., 40: 545, 6.]-E. Malling Res. Stat., Maidstone, Kent.