Design and Experiment of Orchard Air-Assisted Sprayer with Airflow Graded Control

Abstract

The orchard air-assisted sprayer exhibits strong droplet penetration, allowing uniform adhesion on both the front and back surfaces of leaves. The spray deposition and spray drift are influenced not only by the amount of pesticide but also by the airflow provided by the air-assisted system. To meet the requirements for regulating airflow and pesticide application in orchards, a method based on the iris structure for continuous adjustment of the air inlet area was proposed. An airflow control mechanism for orchard air-assisted sprayers, which is easy to install, was developed, and a circular recirculating pressure-stabilized spray system was designed. Additionally, an orchard sprayer supporting graded airflow control was developed. Experiments were conducted to assess airflow variation within the tree canopy and the spray deposition and spray drift under different airflow levels. The results showed that the average airflow attenuation rates in the canopy were 63.0%, 71.8%, and 82.5% for the leaf areas and canopy thicknesses of 826.5 cm², 1409.8 cm², and 1931.1 cm², and 1.5 m, 2.0 m, and 2.5 m, respectively. Graded variable control of airflow based on canopy variation helps improve droplet uniformity within the canopy and reduce spray drift in non-target areas. When the airflow in the middle of the tree canopy exceeds 1.50 m/s, the spray deposition ratio on both sides of the leaves increases to 83.55%, and the coefficient of variation in the droplet deposition on both sides is less than 33.24%. These findings provide support for pesticide precision application and spray drift control in orchards.

1. Introduction

Air-assisted spraying is a method recommended by the Food and Agriculture Organization (FAO) of the United Nations for orchard pesticide application [1]. It is characterized by strong droplet penetration, allowing uniform adhesion on both sides of leaves, and is being rapidly promoted both domestically and internationally [2,3]. Pesticide deposition within the orchard canopy and off-target drift are influenced not only by the spray volume but also by the airflow supply of the air-assisted system [4,5].

During air-assisted spraying, the interaction between droplets, foliage, and airflow significantly affects the distribution of the droplet deposition in the canopy. Proper airflow can stress the droplets, facilitating their movement, causing the tree leaves to bend and deform, reducing canopy density, widening the droplet transport channel, and improving deposition uniformity [6]. The canopy volume and leaf area density of orchard trees vary significantly at different growth stages [7,8]. Even with precise pesticide volume control, insufficient airflow can lead to inadequate deposition inside the canopy, while excessive airflow may blow the pesticide out of the canopy [9,10], resulting in pesticide drift and pollution of the orchard ecosystem [11,12].

Scholars both domestically and internationally have conducted fruitful research on pesticide volume control techniques for air-assisted orchard spraying and have made significant progress [4]. These techniques allow precise control of the pesticide volume based on operational speed and tree targets [13]. With breakthroughs in pesticide volume control, the importance of airflow control has become increasingly evident, making it a current research hotspot. Airflow control in air-assisted spraying is primarily achieved by adjusting the fan speed, deflector angles, inlet area, and outlet area [14].

Khot [15,16] designed an orchard air-assisted sprayer based on outlet area control and found that air volume control at the outlet affects spray performance. Landers [17,18] used a louver-shaped air volume control mechanism, and experimental results showed that it could improve liquid deposition by 30%. Cross’s [19] research indicated that pesticide deposition within the fruit tree canopy could be significantly increased by adjusting the fan speed to achieve low air volume. Qiu [20] and Pai [21] connected sprayers to the power take-off (PTO) shaft of tractors to achieve fan speed variable control, which to some extent regulated the airflow of the sprayer; the control range was small and the precision difficult to maintain. Yan [22] and Dou [23] installed deflectors at the sprayer outlet, adjusting the airflow by independently controlling the angle of each deflector, but during adjustment, interactions between the deflector units affected the control results. Gu [24] designed a sprayer with an adjustable inlet opening size, using changes in the inlet area to control the outlet airflow speed, and conducted laboratory experiments. Mahmud [25] installed an opening size control device at the sprayer inlet and validated through orchard trials that airflow control could improve canopy deposition and reduce drift in non-target areas. Vigo [26] designed a multi-outlet sprayer with duckbill-type adjustable outlets, allowing independent control of the airflow speed at each outlet, though airflow interactions between the outlets still occurred. Jiang [27] designed a multi-duct air-assisted sprayer capable of differentiated airflow supply according to the fruit tree canopy. Orchard trials confirmed the importance of differentiated airflow supply for different canopies; however, during the independent control of airflow for each duct in this air-assisted sprayer, interactions between the airflow of the ducts occur. Doruchowski [28] designed the Crop Adapted Application System (CASA), developed to reduce airflow interactions between ducts during independent air volume control by simultaneously coordinating the control fan speed and inlet area; however, the air volume was regulated by control of the inlet area through an electric actuator, but this approach impacted air volume control accuracy.

The above studies have shown that pesticide volume control systems and airflow control devices for orchard spraying have been designed by scholars, with spraying equipment optimized and developed through laboratory or orchard trials. It has been demonstrated that airflow control helps improve droplet deposition within the canopy and reduces pesticide drift in non-target areas. However, further optimization of the existing airflow control devices and spraying systems was found to be necessary.

To address these issues, this paper proposes a method for continuously adjusting the inlet area based on an iris structure, designs an airflow graded control mechanism and a pressure-stabilizing spraying system, and develops an orchard sprayer that supports graded airflow control. The objective of this study was to evaluate the performance of the airflow graded control mechanism and the impact of graded airflow control on droplet deposition and off-target drift within the fruit tree canopy. These included measuring the outlet airflow speed of the sprayer using sensors, assessing the canopy airflow speed under different airflow grading controls, and using water-sensitive paper to measure the droplet deposition and off-target drift within the canopy. The research findings can provide a reference for the study of variable airflow control technology and equipment in air-assisted orchard spraying.

2. Materials and Methods

2.1. Structure and Principle

2.1.1. Machine Structure and Principle

Figure 1 shows the airflow graded control orchard air-assisted sprayer, which was primarily composed of a tracked chassis, an airflow graded control mechanism, a fan, a spray tank, a control system, and a spraying system. The sprayer was operated via a remote controller, which allowed control over the start and stop of the tracked chassis, the fan drive, and the pump of the spraying system. A throttle handle adjustment was provided to regulate the fan speed and the travel speed of the tracked chassis. Additionally, a generator was fitted to provide continuous power to the sprayer. The main technical parameters of the sprayer are listed in

Table 1. Main technical parameters of orchard air-assisted sprayer.

Parameters	Value
Overall dimensions (L × W × H)	1830 × 1060 × 1040
Airflow inlet diameter adjustment range (mm)	0–600
Airflow inlet area adjustment range (mm2)	0–282,600
Airflow outlet area (mm2)	709,890
Traveling speed (m·s−1)	0–1.2
Rotate speed of Fan (r·min−1)	0–1500
Spray tank (L)	300
Number of nozzles (units)	12
Nozzle spray rate (L·min−1)	0–1.5

.

When spraying, the airflow requirements for fruit trees at different growth stages were met through graded control. The airflow control mechanism was adjusted by rotating the handle to change the central opening size, thereby altering the fan’s inlet area and adjusting the pressure of the spraying system. The fan and spraying system were remotely started, and after the airflow at the sprayer’s outlet and the nozzle spray field had stabilized, the tracked chassis was activated to commence spraying operations.

2.1.2. Airflow Inlet Adjustment Method and Airflow Graded Control Mechanism Design

To achieve symmetrical, continuous, and wide-range adjustment of the airflow inlet, enabling graded variable control of the airflow at the outlet, a method based on an iris structure for regulating the inlet opening of the air-assisted sprayer was proposed. The control principle is shown in Figure 2. In the figure, components 1 to 6 and 19 were the fixed ends, while components 7 to 12 were the movable ends, and components 13 to 18 were the arc segments. The movable end 7 was driven by an external force and rotated around the fixed ends 5 and 19, causing the arc segment 13 to rotate. The simultaneous movement of 7 to 12 drove the rotation of the arc segments, thus controlling the central opening. This allowed for continuous and precise adjustment of the sprayer’s inlet opening.

During the opening and closing process, each arc plate rotates around the central rotational axis. The rotational angle of the i-th arc plate is θ_i, and the functional relationship between the angle rotated by the arc plate after time t and time is derived by Equation (1).

$${\theta }_i\left(t\right)={\theta }_0+kt$$

(1)

In the equation:

• ${\theta }_0$—Initial angle, °;
• k—Rotational speed coefficient;
• t—Rotation time, s.

After time t, the trajectory equation of the endpoint of the i-th arc plate is derived by Equation (2).

$$\left\{\begin{array}{c}{x}_i(t)=D_{max}\cdot \cos \left({\displaystyle \frac{\delta }{2}}\right)\cos ({\theta }_0+kt)\\ y_i(t)=D_{max}\cdot \cos \left({\displaystyle \frac{\delta }{2}}\right)\sin ({\theta }_0+kt)\end{array}\right.$$

(2)

In the equation:

• $\delta$—Arc plate radian, rad;
• D_max—Maximum diameter, mm.

During the opening and closing process of each arc plate, the relationship between the central opening diameter D and time t is derived by Equation (3).

$$D(t)=D_0+(D_{max}-D_0)\cdot {\displaystyle \frac{{\theta }_0+kt}{{\theta }_{max}}}$$

(3)

In the equation:

• $D_0$—Initial diameter, mm;
• ${\theta }_{max}$—Rotational angle at the maximum diameter, °.

In summary, the equation describing the relationship between the central opening area S and time t is derived by Equation (4).

$$S(t)={\displaystyle \frac{1}{4}}\pi {(D_0+(D_{max}-D_0)\cdot {\displaystyle \frac{{\theta }_0+kt}{{\theta }_{max}}})}^2$$

(4)

In the equation:

• $S$—Central opening area, mm².

Assume the transmission ratio between the adjustment handle and the arc plate rotational adjustment plate was $x=m/n$. Substituting $\omega =2\pi n$ and $\theta =\omega t$ into the above equations, the relationship between the inlet area and the handle rotational speed is derived by Equation (5).

$$S(m)={\displaystyle \frac{1}{4}}\pi {(D_0+(D_{max}-D_0)\cdot {\displaystyle \frac{{\theta }_0+k\frac{x{\theta }_{max}}{2\pi m}}{{\theta }_{max}}})}^2$$

(5)

Based on the aforementioned principles and adjustment methods, an airflow graded control mechanism was designed, as shown in Figure 3. It was mainly made of steel material. It was mainly composed of arc plates, an arc plate mounting base, arc plate limiting slots, and an arc plate rotational adjustment plate. One end of the arc plate positioning hole was connected to the base plate’s connection column, while one end of the arc plate limiting column was installed in the limiting slot of the rotational adjustment plate. Multiple arc plates were arranged in an interleaved pattern.

In conjunction with the inlet dimensions of the sprayer fan designed in this study, D_max = 600 mm, ${\theta }_{max}$ = 90°, the adjustment range of the airflow inlet diameter was 0–600 mm, the adjustment range of the airflow inlet area was 0–282,600 mm², the radian of the arc plate was $\delta$ = 3π/4 rad, the transmission ratio between the adjustment handle and the arc plate rotational adjustment plate was x = 36. The relationship between the inlet area S and the number of handle rotations q is derived by Equation (6).

$$S(q)=\pi \left({\displaystyle \frac{10,000}{9}}{q}^2-20,000q+90,000\right)$$

(6)

The airflow graded control mechanism operated by rotating the adjustment handle, which caused the connected bevel gear to rotate, subsequently driving the arc plate rotational adjustment plate to complete the opening and closing of the arc plates. This allowed for the continuous variation of the inlet diameter. The airflow graded control mechanism is shown in Figure 4. The vacuum airflow generated by the rotating fan was drawn into the fan through the inlet of the airflow grading control mechanism. After being rectified by the guiding cone and guiding plate, a uniform arc-shaped airflow field was formed. By adjusting the inlet area, the airflow at the fan’s outlet could be regulated, achieving graded variable control of the airflow.

2.1.3. Design of Annular Recirculating Pressure-Stabilized Spraying System

The annular recirculating pressure-stabilized spraying system primarily consisted of an annular nozzle mounting frame, a pump (LS-535; Zhejiang Luxion Jianxin Agricultural Machinery Co., Ltd., Taizhou, China), an ECU controller (C37; Beijing Yingzhijie Technology Co., Ltd., Beijing, China), a safety valve, a relief valve, a pressure sensor (LC-23; Ningbo Licheng Agricultural Spraying Technology Co., Ltd., Ningbo, China), a flow sensor (model C-3402; Lingli Electronics Technology Co., Ltd., Quanzhou, China), nozzles (Kross; Zhejiang Qiangu Machinery Co., Ltd., Quzhou, China), and a spray tank, as shown in Figure 5. During pesticide application, the inlet of the pump was connected to the spray tank to draw the pesticide. A pressure meter was installed at the pump outlet, which could display the pressure value in real time. The other outlet was connected to a three-way valve, with one portion of the pesticide liquid recirculating back to the spray tank and the other portion supplying the entire system. The pesticide liquid was filtered through a filter; passed through a safety valve, a pressure relief valve, an electric control valve, and a flow sensor; and finally flowed to the nozzle. The flow sensor and pressure sensor collected the flow and pressure values in the pipeline, converted them into pulse signals, and transmitted these signals to the ECU. The ECU then sent pulse signals to control the relief valve and electric control valve, thereby adjusting the flow and pressure within the pipeline. When the pressure sensor detected that the pipeline pressure exceeded the system’s preset value, the ECU opened the relief valve, allowing part of the pesticide liquid to flow back to the spray tank, thereby maintaining stable system pressure.

Equation (7) is used to calculate the nozzle flow rate of the spraying system [29,30].

$$Q={\displaystyle \frac{M{V}_{\mathrm{e}}B}{600N}}$$

(7)

In the equation:

• Q—Nozzle flow rate, L/min;
• M—Application rate per unit area, L/ha;
• V_e—Sprayer travelling speed, km/h;
• B—Sprayer operating width, m;
• N—Number of nozzles, N.

M = 600 L/ha, V_e = 3.6 km/h, B = 5 m, and N = 12. Substituting into the above equation, the result can be obtained as follows: Q = 1.5 L/min. There are 12 nozzles. The selected nozzle is the Kross model, produced by Zhejiang Qiangyu Machinery Co., Ltd., Shaoxing, China.

2.2. Tree Canopy Leaf Area Detection Experiment

The experiment was conducted in the orchard of the National Experiment Station for Precision Agriculture (Xiaotangshan, Beijing). Three distinctly different apple trees were selected for the experiment. To assess the differences in the canopies of the three fruit trees, the canopy point cloud data were obtained based on the LIDAR canopy detection system, as shown in Figure 6. Using the fruit tree canopy leaf area detection model that was constructed in the earlier stage [31], the leaf area information of the three fruit tree canopies was calculated. The equation is as follows.

$$y=0.199x+38.841$$

(8)

In the equation:

• y—Canopy leaf area, cm²;
• x—number of LiDAR point clouds, points.

The characteristic information of the fruit tree canopy is shown in

Table 2. Characteristic parameters of fruit trees.

Tree Number	T1	T2	T3
Tree
Point cloud image
Canopy Dimensions (W × D × H)/m × m × m	1.5 × 1.5 × 2.0	2.0 × 2.0 × 2.5	2.2 × 2.5 × 3.0
Number of point clouds (units)	3958	6889	9509
Canopy leaf area (cm2)	826.5	1409.8	1931.1

.

2.3. Single-Nozzle Flow Rate Measurement Experiment

To measure the flow rate of single nozzles, a nozzle flow rate test was designed using a self-developed nozzle flow testing device [32], as shown in Figure 7. During the experiment, the flow rates of a total of 12 nozzles (Kross; Zhejiang Qiangyu Machinery Co., Ltd., Shaoxing, China), located on both the left and right sides, were measured simultaneously. The nozzles at various positions on the sprayer outlet were labeled as L6, L5, L4, L3, L2, L1, R1, R2, R3, R4, R5, and R6. The nozzle clamp was attached to each nozzle, and the sprayer system was started. The pressure of the sprayer system was adjusted while the reading on the pressure gauge was observed. Once the pressure of the sprayer system stabilized at the desired value, the reading on the testing device was observed, and the data were recorded once the flow rate stabilized. The pressure of the sprayer system was set to 1.0 MPa [20,33], and each test group was repeated three times.

2.4. Outlet Airflow Speed Measurement Test

To investigate the airflow distribution and changes at the fan outlet under different airflow grades, the airflow at the inlet was divided into five different airflow grades based on the fan inlet diameter. The parameters for each airflow grade are shown in

Table 3. Airflow graded control parameter setting.

Control Parameter	Graded 5	Graded 4	Graded 3	Graded 2	Graded 1
Air inlet opening
Opening diameter	600 mm	500 mm	400 mm	300 mm	200 mm
Opening area	282,600 mm2	196,250 mm2	125,600 mm2	70,650 mm2	31,400 mm2
number of rotations	0	1.5	3	4.5	6

. To determine the airflow direction at each nozzle position, the airflow speed calibration method at the sprayer outlet described in reference [30] was referred to. According to the nozzle position numbering described in Section 2.3, a ribbon (1.0 m) was tied at each nozzle position. After the sprayer’s air-assisted system was started, the ribbons were blown by the airflow, and the direction in which the ribbons were blown indicated the airflow direction at each nozzle position. To measure the effect of different fan speeds on the outlet wind speed of the sprayer at the same airflow grade, the fan speed was set to 800 r/min, 1000 r/min, and 1200 r/min. The fan speed was adjusted to the set value, and the inlet opening diameter was set to the required grade for the experiment. An airflow speed sensor (Model: TSI-8455-300; TSI Incorporated, Shoreview, MN, USA; accuracy: 0.01, range: 0–60 m/s) was used to measure the airflow speed at the sprayer outlet along the direction indicated by the blown ribbon. The experimental data were recorded, with each test group repeated three times. The testing scene is shown in Figure 8.

2.5. Fruit Tree Canopy Airflow Speed Measurement Experiment

To measure the airflow speed at different positions within the fruit tree canopy under different airflow grades, an airflow speed sensor (Model: TSI-8455-300, accuracy: 0.01, range: 0–60 m/s) was used. The arrangement of measurement points within the fruit tree canopy is shown in Figure 9.

The airflow speed sensors were fixed at seven positions (A1–A7) in the fruit tree canopy—top, middle, bottom, left side, right side, front, and back—according to references [25,34,35]. The probe of the airflow speed sensor was fixed to one end of a double-headed clamp that could rotate in any direction, with the other end of the clamp secured to the fruit tree branches. The direction of the probe was adjusted to be perpendicular to the ground, and all airflow sensor probes were aligned in the same direction. A reference line was marked 2 m from the center of the canopy to serve as the path for the sprayer’s movement. Based on the canopy characteristics of the experimental fruit tree, the sprayer’s fan speed was set to 1200 r/min during the experiment. The sprayer traveled at a speed of 1 m/s. The airflow speed at each position was recorded in real time using the airflow speed sensors, with each test group repeated three times. The testing scene is shown in Figure 10. During the experiment, a meteorological station was placed 20 m from the test site. The meteorological station recorded an average wind speed of 1.1 m/s, a northerly wind direction, an ambient temperature of 22.65 °C, and a relative humidity of 24.56%.

2.6. Measurement Experiment of Droplet Deposition and Drift in Fruit Tree Canopy

To evaluate the droplet deposition and drift in the fruit tree canopy under different airflow graded control, a droplet deposition and drift measurement experiment was designed, as shown in Figure 8. A total of 14 sampling positions were set. The sampling positions within the fruit tree canopy were the same as the airflow speed sampling positions described in Section 2.5. Water-sensitive paper was placed on both the upper and lower surfaces of leaves at each sampling position, and the paper was fixed using paper clips. To measure droplet drift on the ground, three sampling positions were arranged at equal intervals on the ground based on the width of the fruit tree canopy. To measure airborne droplet drift, four sampling points were arranged behind the fruit tree canopy based on its height and width. Water was used as the spray liquid in this experiment. The testing scene is shown in Figure 11. The experimental procedure was the same as the airflow speed measurement experiment for the fruit tree canopy described in Section 2.5, with each test group repeated three times.

After the experiment, the water-sensitive paper was allowed to dry before being collected from each sampling position into labeled, sealed plastic bags and promptly brought back to the laboratory for analysis [36,37]. A scanner (TSN450, Tiancai Electronics (Shenzhen) Co., Ltd., Shenzhen, China) was used to scan the water-sensitive paper to obtain grayscale images. The images were then analyzed using droplet deposition analysis software (Chongqing Liuliushanxia Co., Ltd., Chongqing, China) to determine droplet deposition and foliar coverage [38,39].

2.7. Data Analysis and Visualization

Statistical analysis was performed using SPSS (version 27.0, IBM, Armonk, NY, USA). In this study, ANOVA was used to determine whether tree number, sampling position, and graded airflow had a significant impact on airflow speed, canopy deposition, and coverage. Three-way ANOVA was conducted, with airflow speed, canopy deposition, and coverage as dependent variables to determine if different trees, sampling positions, and airflow grades resulted in the same values (null hypothesis). If the null hypothesis was not accepted, a Tukey’s post hoc test for a multiple comparison was performed. A confidence level of 95% was considered for all analyses. To visualize the experimental results, three-dimensional bar graphs using Origin software were created (version 2022, OriginLab Corporation, Northampton, MA, USA). Furthermore, bar and scatter plots were created to demonstrate the distribution and trends of data across different categories.

3. Results and Discussion

3.1. Results of Single-Nozzle Flow Rate Measurement Experiment

The results of the single-nozzle flow rate measurement are shown in Figure 12. The average flow rate of a single nozzle was found to be 1.47 L/min, which met the application requirements. The coefficient of variation among the nozzles was calculated to be 0.036, indicating a small discrepancy, which was considered to have little impact on the subsequent experiments on spray uniformity and coverage.

3.2. Measurement Results of Airflow Speed at the Sprayer Outlet

The airflow speed distribution at the sprayer outlet under different fan speeds and airflow grades is shown in Figure 13. It was indicated that the airflow speed at the fan outlet changed significantly. Figure 13a shows the average airflow speed at the sprayer outlet when the fan speed was 1200 r/min. The results indicated that the airflow speed distribution on both sides of the sprayer outlet exhibited the same trend, showing a ‘W’-shaped pattern, and was generally mirror-symmetrical. On the same side, from bottom to top (L6–L1, R6–R1), the airflow speed at each nozzle position first decreased and then increased. The airflow speed was higher at the left and right nozzle positions (L6 and R6) and lower at positions L2, L3, R2, and R3. When the airflow grade was at grade 5, the airflow speed at each nozzle position reached its maximum value. As the airflow grade decreased, the airflow speed at the sprayer outlet decreased accordingly, showing a similar trend. The same results were observed at a fan speed of 1000 r/min (Figure 13b) and a fan speed of 800 r/min (Figure 13c). The experimental results indicated that the use of the airflow graded control device could maintain good consistency in the airflow speed changes at the sprayer outlet.

At the same airflow grade, different fan speeds were compared, and the experimental results indicated that the airflow speed at the sprayer fan outlet changed significantly. As the fan speed decreased, the airflow speed at the sprayer outlet also reduced, while the overall trend remained similar. As shown in Figure 14, the scatter plot illustrates the five airflow control grades and the outlet airflow speed at three different fan speeds. The experimental results demonstrated that the airflow control device was capable of achieving uniform variable control of the outlet airflow speed.

The airflow speed at the left nozzle positions was found to be greater than that at the right positions, which was consistent with the experimental results obtained by Vigo [26]. This phenomenon was caused by the rotational direction of the fan blades. According to the vortex effect and Poincaré’s vortex theorem, when the fan blades were rotated counterclockwise, the airflow from the top blades moved to the right, while the airflow at the bottom moved to the left, forming a vortex. The fan blades moved toward the left side, pushing the surrounding air, which resulted in more active airflow on the left side and a relatively higher airflow speed.

3.3. Measurement Results of Airflow Speed in the Fruit Tree Canopy

As shown in

Table 4. Results of the ANOVA statistical analyses conducted for airflow speed at a confidence level of 95.0%.

Variation Source	Sum of Square	DF	F Value	p Value 1
Model	145.040	104	115.303	1.066 × 10−15 ***
Tree number (TN)	49.895	2	2062.578	8.862 × 10−13 ***
Sampling position (SP)	51.265	6	706.402	3.045 × 10−13 ***
Airflow grade (AG)	32.660	4	675.051	1.301 × 10−11 ***
TN × SP	4.091	12	28.188	1.957 × 10−7 ***
TN × AG	0.408	8	4.221	1.030 × 10−5 ***
SP × AG	4.955	24	17.068	3.988 × 10−7 ***
TN × SP × AG	1.766	48	3.042	2.101 × 10−8 ***

¹ Statistical significance level: (***) p-value < 0.001.

, the ANOVA statistical analyses indicated that tree number, sampling position, and airflow grade all significantly affected airflow speed (Figure 15).

The distribution of airflow speed in the fruit tree canopy under different airflow control grades is shown in Figure 16. For the same fruit tree, the airflow speed within the canopy was found to change significantly under different airflow control grades. As the airflow grade increased, the airflow speed at each position within the canopy also increased, and the trend in airflow speed remained consistent. As the airflow volume at the fan inlet increased, the airflow volume at the fan outlet also increased, resulting in a greater volume of airflow passing through the fruit tree canopy per unit of time. This led to higher airflow speeds at all positions within the canopy.

When the airflow grade was set to grade 5, the airflow speed at all positions within the canopies of the three fruit trees reached its maximum. Among these positions, the highest airflow speed was observed at position A2, which was located at the front of the fruit tree canopy and was closer to the sprayer outlet, resulting in less airflow loss. The airflow speed values at positions A1 and A7 were lower; these positions were located at the top and back of the fruit tree canopy, respectively, and were relatively farther from the sprayer outlet, which resulted in greater resistance and higher airflow loss. Position A6, located in the middle of the fruit tree canopy, between A2 and A7, had an airflow speed greater than that at A7 but less than that at A2. The airflow speed values at positions A3, A4, and A5 were found to be generally similar.

At the same airflow control grade, the airflow speed at the seven positions in the T1 fruit tree canopy was found to be the highest, followed by that in the T2 fruit tree canopy, and the airflow speed at the corresponding seven positions in the T3 fruit tree canopy was the lowest. The T1 fruit tree had a smaller canopy leaf area, while the T3 fruit tree had a larger canopy leaf area. As the leaf area of the fruit tree canopy increased, the resistance also increased, which impeded the airflow from passing through the tree to reach the rear part of the canopy. As a result, more airflow was lost, penetration was weakened, and airflow speed decreased. Under different airflow control grades, the average airflow speed attenuation rates for the T1, T2, and T3 fruit tree canopies were 62.99%, 71.83%, and 82.48%, respectively. Therefore, during air-assisted spraying, to ensure effective leaf agitation within the fruit tree canopy and achieve more uniform droplet deposition on both sides of the leaves, the required airflow for the fruit trees was determined to be in the following order: T3 > T2 > T1.

3.4. Measurement Results of Droplet Deposition and Drift in the Fruit Tree Canopy

As shown in

Table 5. Results of the ANOVA statistical analyses conducted for deposition and coverage at a confidence level of 95.0%.

Variation Source	DF	Deposition				Coverage
		Upper Leaf Side		Lower Leaf Side		Upper Leaf Side		Lower Leaf Side
		F Value	p Value 1	F Value	p Value 1	F Value	p Value 1	F Value	p Value 1
Model	104	404.098	1.025 × 10−12 ***	155.716	4.248 × 10−15 ***	16.113	9.287 × 10−12 ***	17.496	6.451 × 10−15 ***
Tree number (TN)	2	859.201	8.826 × 10−14 ***	161.251	3.710 × 10−13 ***	87.449	2.353 × 10−8 ***	11,588.800	1.080 × 10−11 ***
Sampling position (SP)	6	47.244	2.748 × 10−8 ***	1108.920	5.279 × 10−15 ***	45.744	1.402 × 10−5 ***	75.508	1.962 × 10−9 ***
Airflow grade (AG)	4	28.747	5.664 × 10−8 ***	55.925	4.672 × 10−12 ***	4.684	1.217 × 10−3 **	77.977	9.964 × 10−6 ***
TN × SP	12	14.451	9.636 × 10−10 ***	20.488	2.632 × 10−12 ***	3.025	6.115 × 10−4 ***	3.172	1.475 × 10−11 ***
TN × AG	8	268.771	1.284 × 10−10 ***	11.084	4.950 × 10−13 ***	3.993	1.984 × 10−4 ***	10.145	1.246 × 10−15 ***
SP × AG	24	34.612	1.657 × 10−7 ***	276.671	6.808 × 10−14 ***	31.769	7.126 × 10−5 ***	7.554	7.369 × 10−9 ***
TN × SP × AG	48	404.098	1.025 × 10−7 ***	42.085	2.636 × 10−8 ***	7.853	7.976 × 10−7 ***	28.902	1.256 × 10−5 ***

¹ Statistical significance level: (**) p-value < 0.01; (***) p-value < 0.001.

, the ANOVA statistical analyses indicated that tree type, sampling position, and airflow grade all significantly affected deposition and coverage.

The droplet deposition and coverage distribution on both the upper and lower surfaces of leaves at different positions within the fruit tree canopy under varying airflow control grades, along with the off-target drift measurement results, are shown in

Table 6. Distribution of T1 canopy spray droplets under different airflow grades. Letters represent homogeneous groups obtained through the Tukey’s post hoc test (p ≤ 0.05). Groups with the same letters indicate no significant differences. Standard deviations for the mean are presented in parentheses. Labels A~E represent statistically significant differences in deposition between different airflow grades at the same sampling location. Labels a~d represent statistically significant differences in coverage between different airflow grades at the same sampling location.

T1
Graded		Graded 5		Graded 4		Graded 3		Graded 2		Graded 1
Sampling Location		Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)
Top	Upper	103.11(5.38) D	35.09(2.37) b	110.73(8.72) C	33.44(3.31) b	138.82(4.25) C	33.78(4.90) a	91.12(4.55) B	25.72(3.28) a	58.67(3.08) A	22.5(2.67) b
	Lower	129.42(3.46) C	29.29(5.90) bc	127.84(2.86) C	25.44(2.38) c	127.14(6.75) B	25.13(5.06) a	64.01(3.94) A	19.23(2.12) a	30.85(4.99) B	15.14(2.59) b
Front	Upper	99.56(5.42) C	52.56(8.95) a	97.7(9.72) B	54.57(5.57) b	115.98(4.42) A	55.81(7.05) b	70.62(4.46) D	32.53(2.56) b	50.66(1.93) D	40.25(2.14) b
	Lower	97.56(4.79) A	34.45(4.49) b	109.04(6.84) C	37.23(2.55) a	107.09(3.74) B	45.98(5.05) a	51.56(5.66) E	19.81(2.38) b	44.22(4.01) D	29.31(2.61) a
Bottom	Upper	141.72(7.32) A	33.92(3.28) ab	118.98(5.91) B	45.17(4.59) bc	134.55(3.92) C	46.75(6.34) bc	62.06(4.97) B	40.08(3.86) c	41.35(2.53) B	38.65(3.35) a
	Lower	163.14(5.68) A	30.89(9.28) a	138.67(9.45) D	31.78(1.95) b	123.12(5.18) C	38.06(3.24) a	80.66(4.67) B	13.44(0.52) a	36.53(2.55) D	24.64(3.60) a
Left side	Upper	61.56(3.42) C	44.71(6.33) c	76.93(5.66) D	39.63(2.97) b	84.76(4.56) C	37.56(0.98) b	50.59(7.63) A	40.95(3.05) ab	35.25(4.81) B	25.18(2.20) a
	Lower	40.97(5.09) C	21.31(5.62) b	48.36(7.35) D	39.34(3.71) ab	74.36(4.97) E	29.03(1.21) b	33.45(3.34) A	27.09(4.15) ab	13.54(3.33) B	11.69(1.63) a
Right side	Upper	84.15(7.00) C	43.42(9.67) bc	66.67(5.02) A	41.39(6.76) b	64.87(5.01) B	40.32(5.24) a	41.52(6.28) AB	22.32(2.10) c	20.48(3.77) C	26.47(3.65) c
	Lower	55.98(6.03) D	28.43(6.56) a	44.77(7.01) A	28.26(2.07) b	83.08(3.85) B	36.39(1.17) a	58.81(4.68) A	26.69(1.36) c	19.57(4.13) C	18.18(2.63) b
Middle	Upper	83.11(6.24) A	38.35(4.70) a	81.33(5.31) A	39.33(3.68) b	86.54(3.33) D	23.72(4.20) b	21.52(3.63) B	26.32(2.99) b	15.16(2.41) C	29.45(3.94) b
	Lower	82.95(4.59) B	22.78(2.94) a	78.57(8.67) A	22.78(3.17) ab	94.85(4.11) D	29.59(3.55) c	44.56(6.35) C	28.01(2.59) b	25.86(3.79) E	19.33(3.93) ab
Backside	Upper	48.36(3.18) D	31.86(2.44) bc	54.35(5.78) B	31.55(4.06) bc	73.11(6.78) B	35.05(1.93) b	45.66(5.12) C	29.07(3.02) a	10.41(2.37) A	29.22(4.12) d
	Lower	50.97(6.17) BC	22.82(2.69) c	66.09(6.80) B	22.11(3.34) b	65.56(6.28) C	30.34(0.36) ab	31.81(4.74) C	10.08(1.54) bc	14.25(2.16) A	12.08(1.63) a

,

Table 7. Distribution of T2 canopy spray droplets under different airflow grades. Letters represent homogeneous groups obtained through the Tukey’s post hoc test (p ≤ 0.05). Groups with the same letters indicate no significant differences. Standard deviations for the mean are presented in parentheses. Labels A~D represent statistically significant differences in deposition between different airflow grades at the same sampling location. Labels a~e represent statistically significant differences in coverage between different airflow grades at the same sampling location.

T2
Graded		Graded 5		Graded 4		Graded 3		Graded 2		Graded 1
Sampling Location		Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)
Top	Upper	116.97(3.61) B	29.99(6.22) d	123.04(6.78) A	24.12(6.28) c	98.98(8.62) C	23.11(3.36) b	51.47(3.55) B	20.57(2.51) a	18.02(2.44) C	9.42(1.45) e
	Lower	99.83(3.81) D	38.98(3.28) b	99.6(4.06) B	30.89(2.52) c	71.48(4.87) A	26.45(1.61) c	40.25(5.26) C	20.52(3.10) a	12.73(3.20) D	10.18(1.04) c
Front	Upper	104.55(6.01) A	42.19(3.80) b	118.94(5.34) B	44.57(4.69) a	81.23(4.18) B	44.72(3.58) c	50.79(2.25) C	46.08(4.06) d	31.45(3.48) C	49.65(5.19) c
	Lower	85.09(4.13) A	31.83(4.14) b	94.47(7.87) B	29.56(6.40) a	107.97(7.28) B	25.63(1.76) b	48.15(4.10) C	34.01(3.57) c	24.89(1.64) C	29.31(2.58) c
Bottom	Upper	118.83(5.60) A	46.51(5.57) c	109.09(8.04) D	35.17(4.42) c	104.59(3.79) D	33.95(2.95) b	66.75(5.21) C	38.89(2.09) a	21.34(2.89) B	40.02(4.52) bc
	Lower	109.04(8.38) A	31.44(3.17) a	108.24(7.09) C	21.78(1.91) c	118.81(8.18) B	20.14(3.13) a	69.12(8.24) B	20.93(3.49) ab	56.44(2.57) B	12.46(3.35) bc
Left side	Upper	93.96(7.08) D	39.95(3.48) c	99.83(7.95) B	28.96(3.67) a	65.37(4.59) C	29.68(3.55) c	59.08(5.04) A	26.56(2.60) bc	58.77(3.74) B	28.58(4.51) ab
	Lower	89.42(4.01) D	21.63(5.61) c	87.03(5.07) BC	35.23(4.36) a	84.82(5.28) C	25.89(2.78) ab	19.53(1.41) A	17.98(2.50) c	43.81(2.30) AB	11.69(3.04) ab
Right side	Upper	60.19(4.43) C	43.42(3.29) bc	76.93(5.29) BC	29.24(5.87) b	78.49(5.05) AB	47.32(1.04) a	35.22(1.61) A	42.78(2.63) c	30.92(1.53) D	16.41(1.68) b
	Lower	85.09(5.32) C	48.43(8.51) c	93.86(6.38) A	28.26(4.69) bc	90.13(9.83) BC	31.39(2.70) b	18.54(1.18) AB	21.92(3.45) a	14.58(4.51) D	18.88(1.15) ab
Middle	Upper	50.17(6.60) C	38.01(5.25) c	78.83(8.52) BC	25.56(3.36) b	52.14(2.90) AB	32.56(1.68) a	18.35(1.29) A	32.66(5.32) bc	15.35(3.46) D	17.45(2.75) b
	Lower	81.91(6.62) C	14.36(3.84) a	85.91(3.39) A	22.05(1.55) bc	34.99(2.59) C	19.08(2.15) b	16.54(3.54) B	25.53(5.83) c	15.76(0.81) D	5.33(1.14) bc
Backside	Upper	38.45(7.38) D	18.63(2.35) c	44.35(3.53) C	33.55(2.91) b	23.11(1.91) C	35.24(2.37) bc	18.09(1.29) B	21.15(4.35) bc	21.55(3.28) A	9.42(1.17) a
	Lower	21.25(1.06) C	12.82(2.82) c	30.09(4.65) B	23.78(3.09) c	20.56(1.25) B	19.99(1.65) a	11.15(1.61) B	14.06(2.10) c	10.87(1.94) A	10.01(0.74) b

,

Table 8. Distribution of T3 canopy spray droplets under different airflow grades. Letters represent homogeneous groups obtained through the Tukey’s post hoc test (p ≤ 0.05). Groups with the same letters indicate no significant differences. Standard deviations for the mean are presented in parentheses. Labels A~E represent statistically significant differences in deposition between different airflow grades at the same sampling location. Labels a~d represent statistically significant differences in coverage between different airflow grades at the same sampling location.

T3
Graded		Graded 5		Graded 4		Graded 3		Graded 2		Graded 1
Sampling Location		Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)	Deposition (drop/cm2)	Coverage (%)
Top	Upper	80.32(4.68) A	34.92(4.30) c	72.36(4.62) B	33.12(2.78) a	59.31(5.07) B	28.19(3.49) b	33.72(3.25) B	24.47(2.84) a	11.78(1.43) C	14.42(1.71) c
	Lower	99.26(6.51) B	27.08(3.13) a	88.46(5.93) B	28.07(3.84) b	70.16(6.61) A	20.81(4.93) a	45.39(5.52) A	14.32(4.11) b	6.96(1.68) C	5.28(1.42) c
Front	Upper	120.68(7.16) A	28.57(3.32) a	125.59(5.58) A	40.65(5.89) a	88.23(5.89) B	33.72(5.56) b	55.88(4.88) C	32.29(2.33) d	20.325.62) C	26.91(2.02) c
	Lower	115.09(2.95) A	33.13(4.93) a	91.99(4.09) B	26.78(2.76) a	108.09(7.83) B	23.81(1.08) ab	63.55(3.36) D	20.01(4.77) c	39.83(3.68) C	10.31(0.84) bc
Bottom	Upper	99.93(5.79) A	36.23(7.57) bc	109.24(6.48) C	25.27(3.82) cd	99.91(5.51) C	23.09(3.46) d	59.23(3.23) B	33.99(2.71) a	26.86(2.56) B	20.09(2.89) ab
	Lower	89.04(3.93) A	43.46(6.05) a	80.88(7.07) D	30.18(4.94) b	109.88(7.13) C	20.06(5.17) b	69.12(6.08) B	20.93(5.20) b	41.52(8.22) B	17.66(1.82) b
Left side	Upper	101.24(6.90) D	44.92(6.30) c	109.13(3.10) C	38.99(7.09) a	65.37(3.81) C	30.87(1.80) ab	44.96(4.72) A	29.61(3.01) c	21.29(3.16) B	27.89(2.78) ab
	Lower	91.19(2.77) C	26.39(3.70) c	82.37(8.20) B	25.98(3.43) a	85.25(6.44) B	20.22(2.26) b	30.23(5.90) A	19.44(0.94) b	23.68(6.44) A	10.44(0.66) ab
Right side	Upper	109.82(5.65) C	33.81(5.38) a	66.91(5.66) A	49.11(5.48) b	54.89(8.16) B	42.22(5.43) a	45.67()3.39 C	38.43(1.94) ab	33.63(3.80) D	14.25(0.26) b
	Lower	90.12(8.68) B	28.43(2.57) a	89.213(6.37) A	28.78(2.63) a	89.69(1.90) A	31.04(3.23) a	30.41(5.16) C	19.94(3.59) a	22.09(4.42) D	17.39(1.13) b
Middle	Upper	60.59(5.33) A	28.99(3.67) b	48.83(4.29) B	25.22(4.13) bc	32.18(4.73) E	21.68(3.79) d	20.88(4.10) D	18.73(2.50) c	10.98(2.13) C	19.95(2.58) a
	Lower	67.97(2.48) A	22.77(2.48) a	54.59(5.12) B	12.33(1.30) b	44.27(3.53) E	10.96(1.33) c	19.23(3.28) D	9.43(1.09) c	15.92(1.87) C	10.35(2.49) ab
Backside	Upper	33.37(3.32) C	21.52(2.20) c	24.98(1.63) B	6.65(1.07) bc	19.23(2.92) A	25.12(3.74) b	15.09(2.44) A	20.12(3.05) a	9.52(1.34) A	8.01(1.69) ab
	Lower	28.53(2.24) D	10.03(1.06) c	26.64(2.85) C	6.99(1.52) b	16.62(2.07) A	11.94(1.35) b	10.15(1.01) AB	15.36(1.55) b	2.81(0.83) B	4.32(1.17) a

and

Table 9. Distribution of Non-Target droplets drift coverage from T1, T2, and T3 fruit trees under different airflow grades. Letters represent homogeneous groups obtained by the Tukey’s post hoc test (p ≤ 0.05). Groups identified by the same letter did not differ significantly. Standard deviation for the mean is presented in parenthesis.

Graded		Graded 5	Graded 4	Graded 3	Graded 2	Graded 1
Test Tree	Sampling Location	Coverage (%)	Coverage (%)	Coverage (%)	Coverage (%)	Coverage (%)
T1	Ground	12.75(1.95) c	5.26(1.03) d	5.85(1.15) b	25.55(2.32) b	34.47(2.57) a
	Air	23.73(2.61) a	13.19(1.10) b	5.31(1.36) c	1.54(0.34) d	1.43(0.57) d
T2	Ground	21.83(1.87) ab	15.92(1.91) d	19.38(1.67) bc	19.95(2.58) bc	24.31(0.40) a
	Air	13.43(2.73) a	8.43(0.74) b	8.31(1.37) b	1.54(0.40) c	1.43(0.45) c
T3	Ground	15.83(1.46) c	27.23(2.86) b	29.83(2.42) b	30.46(2.06) b	35.96(1.15) a
	Air	10.03(1.70) a	9.95(0.98) a	3.31(0.55) b	1.43(0.45) c	0.43(0.36) c

, respectively. Differences in droplet deposition and coverage between the upper and lower surfaces of the fruit tree canopy leaves were observed. For the three fruit trees, as the airflow control grade was reduced, the deposition and coverage on the upper part of the canopy, as well as on the ground and in the air, were gradually decreased. With the reduction in airflow control grade, the airflow speed reaching the canopy was diminished, and the ability to transport droplets to or through the top of the canopy was weakened. Airflow speed was found to be greater at the front, upper, and lower parts of the fruit tree canopy. Through water-sensitive paper tests, it was observed that deposition at these positions was greater compared to other positions. In contrast, airflow speed was lower in the middle and rear parts of the canopy, resulting in reduced deposition.

For the T1 fruit tree, when the airflow grade was at graded 1, the droplet deposition on both sides of the leaves at the left side, right side, middle, and backside of the fruit tree canopy was less than 20 drop/cm², which, according to the General Test Method for Plant Protection Machinery JB-T 9782-2014 [40], does not meet the requirements for air-assisted spraying for pest and disease control. When the airflow grade was at graded 2, 3, 4, and 5, the droplet deposition ratios on both sides of the leaves were 66.52%, 85.91%, 72.59%, and 67.87%, respectively. The coefficients of variation for droplet deposition on both sides of the leaves are 36.16%, 26.45%, 34.75%, and 41.50%, respectively. In summary, airflow graded 3 is more suitable for spraying the T1 fruit tree, and at this airflow grade, the airflow speed in the middle of the fruit tree canopy is 1.76 m/s.

For the T2 fruit tree, when the airflow grade was at graded 1 and 2, the droplet deposition on both sides of the leaves at the top, left side, right side, middle, and back of the fruit tree canopy was less than 20 drops/cm², which did not meet the requirements for air-assisted spraying for pest and disease control. When the airflow grade was at graded 3, 4, and 5, the droplet deposition ratios on both sides of the leaves were 68.36%, 86.61%, and 77.11%, respectively. The coefficients of variation for droplet deposition on both sides of the leaves were 42.37%, 29.20%, and 35.94%, respectively. In summary, airflow graded 4 was found to be more suitable for spraying the T2 fruit tree, and at this airflow grade, the airflow speed in the middle of the fruit tree canopy was 1.55 m/s.

For the T3 fruit tree, when the airflow grade was at graded 1 and 2, the droplet deposition on both sides of the leaves at the upper, middle, and rear parts of the fruit tree canopy was less than 20 drop/cm², which does not meet the requirements for air-assisted spraying for pest and disease control. When the airflow grade was at graded 3, 4, and 5, the droplet deposition ratios on both sides of the leaves were 67.76%, 72.65%, and 83.55%, respectively. The coefficients of variation for droplet deposition on both sides of the leaves were 46.35%, 39.11%, and 33.24%, respectively. In summary, airflow graded 5 was more suitable for spraying the T3 fruit tree, and at this airflow grade, the airflow speed in the middle of the fruit tree canopy was 1.50 m/s.

As shown in Table 9, for the T1, T2, and T3 fruit trees, as the airflow grade increased, the airborne droplet coverage gradually increased, indicating greater airborne drift of droplets, while ground drift gradually decreased. This was likely due to the increased airflow, which enhanced droplet penetration through the tree canopy or carried more droplets around the canopy top to reach the next row. At lower airflow grades, airborne drift was reduced, possibly because the leaf area density within the canopy was higher, obstructing the airflow from carrying droplets through the canopy. Under the condition of meeting the requirements for air-assisted spraying for pest and disease control, for T1 trees, graded 3 and 4 exhibited less ground drift. In terms of airborne drift, graded 3 showed less airborne drift, further confirming that airflow graded 3 was more suitable for spraying the T1 fruit tree. Similarly, for spraying the T2 fruit tree, airflow graded 4 was more suitable, and for spraying the T3 fruit tree, airflow graded 5 was found to be more suitable.

Based on the above analysis, it was concluded that it is crucial to grade and regulate the airflow supply of the air-assisted sprayer according to the variation in the fruit tree canopy leaf area. When the wind speed in the middle of the canopy exceeds 1.50 m/s, the droplet deposition ratio on both sides of the leaves in the fruit tree canopy is greater than 83.55%, and the coefficient of variation for droplet deposition on both sides of the leaves is less than 33.24%.

4. Conclusions

(1)

A continuous air inlet area adjustment method based on an iris structure was proposed, and an airflow graded control mechanism, along with an annular recirculating pressure-stabilized spraying system, was designed. An airflow graded control orchard sprayer was developed, which allowed for the continuous adjustment of the air inlet area. The air inlet diameter adjustment range was 0–600 mm, and the air inlet area adjustment range was 0–282,600 mm². Additionally, the system was modified to be motor-driven in subsequent research, enabling future automatic control.

(2)

Experiments were conducted to measure the air outlet airflow speed distribution of the sprayer at different fan speeds and control grades. The results showed that the airflow speed trends on both the left and right sides of the sprayer outlet were consistent and generally mirror-symmetrical. The airflow speed at various nozzle positions followed a “W”-shaped distribution, first decreasing and then increasing. The graded airflow control mechanism was found to achieve effective variable control of the air outlet airflow speed.

(3)

Three fruit trees with canopy leaf areas and thicknesses of 826.5 cm², 1409.8 cm², and 1931.1 cm² and canopy heights of 1.5 m, 2.0 m, and 2.5 m, respectively, were selected for the canopy airspeed measurement experiment under different control grades. The results indicated that under the same airflow supply, differences in canopy leaf area affected airflow speed loss within the tree canopy. The average airflow speed attenuation rates for the three trees were 63.0%, 71.8%, and 82.5%, respectively. When applying air-assisted spraying, differentiated airflow supply was required based on the canopy leaf area to ensure uniform leaf movement and droplet deposition on both sides of the leaves.

(4)

Droplet deposition and drift experiments were conducted under different control grades, and the optimal grade for the three test trees was determined. Graded airflow control based on canopy leaf area during air-assisted spraying was shown to improve droplet deposition uniformity within the canopy and reduce droplet drift in non-target areas. When the airflow speed in the middle of the canopy exceeded 1.50 m/s, the droplet deposition ratio on both sides of the leaves in the canopy increased to 83.55%, and the coefficient of variation for droplet deposition fell below 33.24%.