Interactive Effects of Traction Speed and Operating Distance on Spraying Performance of an Air-Assisted Sprayer in Apple Orchards

This study aims to investigate the effects of operating distance and traction speed on droplet characteristics, deposition distribution, and pesticide deposition efficiency of an air-assisted sprayer in apple orchards, and to clarify the interaction mechanism between these two parameters, so as to provide a theoretical basis for precision spraying in orchards.

A two-factor field experiment was conducted in a wide-row densely planted apple orchard using an SS-1000 self-propelled air-assisted sprayer. Three operating distances (0, 0.5, and 1.0 m) and three traction speeds (2.48, 4.10, and 5.98 km·h^-1) were set, resulting in nine treatment combinations. The droplet size (volume median diameter, VMD), droplet density, and droplet coverage were measured using the water-sensitive paper method. Foliar deposition and ground deposition were determined using the Allura Red tracer method combined with spectrophotometry, and the pesticide deposition efficiency was calculated. Range analysis and analysis of variance were employed to evaluate the main effects and interactions of the factors.

At the same operating distance, as traction speed increased, droplet size, droplet coverage, foliar deposition, and ground deposition exhibited a decreasing trend, while droplet density and pesticide deposition efficiency showed an increasing trend. At the same traction speed, as operating distance increased, droplet size and density increased, whereas droplet coverage, foliar deposition, and pesticide deposition efficiency showed opposite trends. The ratio of inner to outer canopy deposition ranged from 0.400 to 0.682, with the highest value (0.682) observed at the combination of 0 m operating distance and 2.48 km·h^-1 traction speed. Orthogonal analysis revealed that the order of factors influencing foliar deposition was traction speed > interaction between traction speed and operating distance > height > operating distance. Traction speed had a highly significant effect on foliar deposition (P < 0.01), the interaction between operating distance and traction speed showed a significant effect (P < 0.10), while height had no significant effect (P > 0.25). The optimal combination for maximizing foliar deposition was 0 m operating distance and 2.48 km·h^-1 traction speed. For ground deposition, the order of influencing factors was traction speed > operating distance > direction > interaction, and the optimal combination for minimizing ground deposition was 0 m operating distance, 5.98 km·h^-1 traction speed, and north direction. A regression model (R² =0.90) confirmed the antagonistic interaction between operating distance and traction speed, and the predicted optimal parameters (0 m, 2.48 km·h^-1) were consistent with the measured results.

Operating distance and traction speed exhibit a significant antagonistic effect on spraying performance, meaning that operating distance negatively regulates the effect of traction speed. As the operating distance increases, the sensitivity of traction speed's impact on deposition decreases. The combination of short distance and low speed is conducive to improving inner canopy deposition and pesticide deposition efficiency. The combination of long distance and high speed can enhance operational efficiency, but tends to result in insufficient canopy penetration and increased ground loss. Therefore, in practical production, operating parameters should be synergistically optimized according to the control objectives.