Quantifying the influence of pruning treatments on olive tree architecture using UAV technology, 3D models and object-based image analysis

Abstract

Olive tree pruning is one of the most important crop management tasks and becomes a costly practice with implications in harvesting, nutrition, pest and disease control, or irrigation strategies. The type and intensity of the pruning strategy modifies the tree crown with a different degree of severity, which notably affects tree physiology, olive growing and fruit quality. In this research, it is reported a procedure based in combining UAV technology and advanced OBIA methodology to reach highthroughput quantification and detailed three-dimensional (3D) monitoring of an olive tree plantation in which their trees have been affected by three different pruning treatments (traditional, adapted and mechanized). Three flights were performed over the olive plot (before pruning, one month after pruning and almost a year after pruning) and interesting differences could be discerned among all analyzed variables for every tree: crown projected area, tree height and crown volume. The OBIA algorithm used achieved high percentages of trees correctly defined in all analyzed dates except in the areas where DSM had been generated with a lower accuracy. It was checked the olive trees located under adapted pruning, the treatment where a large amount of foliage was removed, showed the highest foliage extraction after pruning followed by trees under traditional pruning, but also experienced higher growths than the other ones, being quantified this response vegetative almost a year after pruning. The trees corresponding to the mechanized pruning treatment kept a more constant vegetative growth along the research. Due to there is almost no information about the assessment of different pruning treatments on the olive tree crown by UAV technology, this research opens the doors towards a wide study area in the agronomical sector, with interesting applications in precision oliviculture although also possibly in other woody crops.