Use of a below-canopy sensing system and vegetation indexes to characterize canopy light and water status of pedestrian olive orchards

Vegetation indexes may provide useful quantitative and qualitative information on light conditions within the canopy. Different vegetation indexes were used to evaluate the effect of pruning on medium to high density pedestrian olive growing systems. Specifically, nine-year-old 'Cerasuola' trees trained to central leader (CL) and spaced at 2×5 m or trained to vase (V) and spaced at 4×5 m were pruned in September and October 2022, and in February 2023. Pruning consisted primarily of eliminating vigorous suckers impairing light interception and reserve accumulation. An AMS 12-spectral-band radiometer (AS7262-visible; AS7263-near infrared) was positioned 30 cm from the ground and 20 cm from the trunk of each tree in trial. Normalized difference vegetation index (NDVI), green normalized difference vegetation index (GNDVI), green leaf index (GLI), normalized difference NIR/RedEdge index (NDRE), and ratio vegetation index (RVI) were calculated from radiometer measurements. Significant effects of pruning were detected only by NDVI, GNDVI and RVI in two out of five dates. NDVI, GNDVI and RVI were lowered by pruning indicating lower canopy thickness, but only in trees trained to vase. No radiometric index was able to detect differences between pruned and non-pruned CL trees, suggesting that sucker removal did not significantly improve light penetration levels in those trees. The same indexes were directly related to stem water potential, indicating some usefulness of this on-tree monitoring system to estimate water status. These preliminary results suggest that GNDVI, NDVI and RVI may be useful, quick and non-destructive tools to establish optimal light conditions and pruning needs in olive trees grown under open training systems.