Exploring variable air flow rate as a function of leaf area index for optimal spray deposition in trellised vineyards

In 3D crops, excessive fan airflow speed may reduce deposition and increase spray losses due to canopy compression. To solve this problem, variable fan airflow rate as a function of canopy characteristics is a key in the context of a sustainable crop protection technology. The effects on spray canopy deposition of different air volume rates (low, medium, and high) generated by a 700 mm diameter axial fan, combined with 4 and 8 km h-1 forward speed, were assessed in a vineyard at an early and late growth stage. The objective was to identify the fan airflow setting (m3 h-1) which maximizes canopy spray deposition (% of applied) with the final aim to determine the relationship between leaf area index (LAI) and optimal fan airflow rate. The results confirmed that an excessive airflow rate significantly decreases spray deposits. When the forward speed increased from 4 to 8 km h-1, the airflow rate had to be increased from low to medium to maximize canopy spray deposition. The results showed the importance of total air volume applied per hectare (m3 ha-1) as a parameter to maximize the spray deposits, irrespective of forward speed. Finally, the relationship between the LAI (adim.), accounting for crop characteristics and canopy density, and the total air volume applied (m3 ha-1) to maximize the canopy spray deposition was identified.