Detecting biophysical and geometrical characteristics of the canopy of three olive cultivars in hedgerow planting systems using an UAV and VIS-NIR cameras

The success of olive (Olea europaea) orchards depends on the interaction between genotype, planting system and orchard management. Research efforts often collide with the lack of high-throughput monitoring technologies for effective and rapid evaluation of expressed phenotypes under field conditions. Rapid phenotyping technologies allow to acquire a large amount of information in a relatively short period, optimizing efforts and labor. In an experiment carried out in Sicily, an unmanned aerial vehicle (UAV) equipped with VIS-NIR cameras was used to monitor canopy characteristics of three olive cultivars (‘Koroneiki’, ‘Biancolilla’ and ‘Calatina’), planted at three different planting distances (PD) (4×4, 4×3 and 4×2 m). Vegetative indices and canopy geometrical characteristics were calculated by means of the map algebra technique and structure from motion technique, respectively. Significant differences in the normalized differential vegetation index (NDVI) and green normalized differential vegetation index (GNDVI) values were measured for the different combinations of cultivars and PD. In particular, the highest and lowest values of NDVI and GNDVI indices were measured in Koroneiki (4×4 m) and ‘Calatina’ (4×3 m) plots, respectively. There was a linear relation between NDVI and pruning removed, expressed on both mass and volume per tree, for all cultivar × PD combinations. Tree canopy volume, estimated by the UAV-VIS camera technique, was higher in Koroneiki than in ‘Calatina’, with intermediate values measured in ‘Biancolilla’. The more spaced trees (4×4 m) had bigger canopies (6.4 m3) than those planted at 4×2 m (5.7 m3), but when the volume was expressed as m3 of canopy per m2 of soil the opposite trend was observed. The higher canopy volume per square meter was related to a higher fraction of intercepted PAR measured at noon. Our results indicate potential application of the UAV-VIS-NIR technique to determine canopy characteristics of different planting systems and cultivars of olive.