Total and diffuse light distribution within the canopy of an apple orchard as affected by reflective ground covers

In recent years, anti-hail nets have been increasingly used to protect apple orchards. As they reduce the light intensity at canopy level, reflective ground covers are frequently placed on the soil surface before fruit harvest with the main aim to enhance color development in bicolored apples. It is not clear however, to which extent the light penetration inside the whole canopy is affected by the reflective ground covers. We performed a study in an intensively cultivated apple district of South Tyrol (northern Italy), with and without reflective ground covers. We measured light intensity at different heights from the ground and different distances from the tree trunk, using two instruments: an 80- cm long ceptometer and a point-like sensor capable of measuring the diffuse radiation component in addition to the total visible light. We found that the reflective ground cover significantly increased the quantity of diffuse light reflected from the orchard floor. The largest effect was recorded at 1 m height from the ground, but it was still significant at 2.5 m height. The influence of the reflective ground cover was particularly remarkable when sun and tree lines were aligned. The increase of total PAR inside the canopy due to the reflective material was however relatively small, suggesting a moderate effect on tree photosynthesis and therefore on apple yields.