Identification of light availability in different sweet cherry orchards under cover by using non-destructive measurements with a Dualex™

Changing climatic conditions makes the development of cultivation strategies for protected cherry cultivation necessary. The objective of the present study was to investigate physiological processes in connection with light availability in different planting systems under cover using a Dualex™ for non-destructive measurements. Hence, cherry trees were either trained as hedgerows, i.e. the most dense planting ([2.35m*2]*1.5m), or trained as spindles (2.70m*2.0m; 1.75m*2.9m) and grown under cover or in the open field at Klein-Altendorf near Bonn, Germany. There was no difference in leaf area between the plantings. Non-invasive measurements with the Dualex™ (Force A, France) showed that a larger relative leaf chlorophyll content (Chl=30–33) in the hedgerow trees under crop cover as a result of less light than in the open field-grown leaves with less chlorophyll (ChI=26–28). Similarly, the flavonoid index (Flav), as a relative measure of the epidermal flavonoids and light condition, was generally lower under crop cover and lowest in the hedgerow trees on the adaxial leaf side with Flav=1.4–1.5 relative to 1.6–1.8 in the open field, but always maintained these high values above the critical light level of 1–1.2. Non-invasive SunScan measurements showed light reductions of up to 80% inside the canopy of the dense hedgerow trees under cover in line with the lowest values for Flav and ChI. Although the largest yield per tree was obtained in the planting system with the best light conditions (1.75m*2.9m), the largest yield per acreage was found in the most dense planting (2.7m*2.0m) with hedgerows under cover as an ideal combination of a high yield and fruit quality with good light availability. Overall, our results showed that light availability depends on crown structure, planting system and tree density. The indices Flav and ChI offer the possibility to evaluate the light conditions in an orchard easily and to give a recommendation for an optimized growing system.