Effects of covering inter-row orchard floor with reflective films on light distribution, photosynthesis, coloration and quality of ‘Fuji’ apples

Abstract

The effect of hot and dry summers, typical of Mediterranean climates, together with inappropriate canopy management, strongly restricts apples red color development. The ‘Fuji’ apples market demands not only fruits with larger sizes, crunchy textures and sweet flavors but also with intense and complete red coloration skin. Portuguese growers face additional difficulties by the predominance of old clones and fast-changing needs of the market, requiring a different technical approach and the introduction of new technologies. The use of reflective materials between tree rows is known by its effects on enhancing red color development without reducing fruit quality and it was tested in Portuguese conditions in an orchard of ‘Fuji Fubrax’ apple (Malus domestica). White polypropylene UV-stabilized reflective film, Reflectex® (Carreta Tessitura, Carre, Italy), was installed 22 days before the first harvest, in alternate rows, leaving uncovered the first 50 cm closer to the trunk. PAR reflection measured at 50 cm height, in the middle of the rows with spontaneous vegetation increased from 9.1 to 53.6% when covered with white reflective film. In spite of soil PAR reflection measured under the canopy at solar noon be low, average reflection in the first linear meter increased from 3 to 11% in the west side and from 1 to 6.5% in the east side, with significant gains in the first 50 cm due to the effect of the film. There was also a positive effect on the side of the trees without film, resulting from reflected radiation into the canopy. These differences were responsible for higher photosynthetic rates measured outside and inside the trees with the film placed laterally, some of these results being supported by chlorophyll content index and specific leaf area measurements. Covering the orchard floor with reflective films was very effective in improving fruit coloration (lower hue values, so redder fruits), showing significant differences and similar color between fruits harvested inside the canopy from the side with the film and fruits from the outside of the canopy without film. Positive effects were also found in average fruit weight, firmness and total soluble solids (increase of about 5-10% in Brix values). These results should be confirmed in a long-term program and others reflective materials assessed.