Morphological changes and spray coverage of pear leaves and canopy at different phenological periods during air-assisted spraying

The airflow of air-assisted spraying in orchards can effectively promote the deformation of leaves and canopies, broaden the droplet transport channels, and improve the uniform of droplet deposition. In this study, the single pear leaf and tree canopy were treated as research objects for micro and macro analyses. The morphological changes and spray coverage of leaves and canopies at the young fruit stage and fruit expansion stage were investigated from the micro and macro perspectives through wind tunnel experiments. Two high-speed cameras were utilized to record the morphological changes of pear leaves and canopies under wind speeds and the multi-point anemometer was used to measure the wind speed attenuation within the canopy. The image processing method was used to obtain the leaf windward area and spray coverage, canopy windward area, optical porosity and spray coverage. The experiments showed that the morphological changes and spray coverage of single leaves and canopies were moderately consistent. The leaf elastic modulus under different phenological periods affected the morphological changes of leaf and canopy, which together with the leaf surface contact angle affected the spray coverage. Within the experimental parameters, the highest total spray coverage in the pear canopy was observed at a wind speed of 6 m s⁻¹ and the spray application was reduced by approximately 36.96 %. In the orchard air-assisted spraying, considering the spray coverage of single leaf and canopy, it is recommended that the wind speed for pear trees at young fruit stage and fruit expansion stage are 3.5–6 m s⁻¹ and 5–7 m s⁻¹, respectively. This study proposes to adopt various spraying parameters at different phenological periods, which can provide a reference for the adjustment of spraying parameters and the optimization of spraying system.