Laser scanning estimation of relative light interception by canopy components in different grapevine training systems

The fractional light interception by different parts of vines trained to various systems was estimated by a modified point-quadrat method using an over-row solar arc positioning device equipped with a laser to simulate sunbeam position and angle at any latitude and time of the day. Laser readings were also combined with total vine light interception estimates via a line sensor to calculate the total light intercepted by specific canopy components. At each sampling date (late June and September, corresponding to fruit set and full canopy), type and position of organs were directly detected by the laser beam. Regardless of sampling date, the relative amount of light captured by the renewal-fruiting area (nodes 1 to 6) of simple cordon (SC) and double curtain (GDC) was considerably higher than that of spur-pruned cordon (SPC), whose vegetative area (distal to node 6) received about two-thirds of the incoming light. Relative light interception by main and lateral leaves was rather constant for GDC, thus reflecting the negligible regrowth after topping. By contrast, SC and SPC showed a much stronger response to topping which caused an increase of light interception by laterals (+19 % for SC and +21 % for SPC). Frequencies of relative intercepted light by main leaves as a function of node position showed a peak around nodes 6-8, a zone where maximum leaf size is attained in all systems and on all dates. Instead, lateral leaves predominantly exposed to light were within the three basal nodes of the lateral shoots. Estimates of relative and total light for different vine parts at any time during the season as detected by laser scanning can objectively assess important characteristics of grapevine training systems, e.g. cluster and basal node exposure to light.