Spray Deposition and Distribution on Rice as Affected by a Boom Sprayer with a Canopy-Opening Device

Abstract

In China, rice growers predominantly use boom sprayers. However, boom sprayers have several drawbacks related to poor penetration in the middle and late stages of rice growth. Several studies have shown that the use of the canopy-opening device can improve droplet deposition in the middle and under layers of rice. Some growers doubt the efficacy of canopy-opening boom sprayers, whereas others have questions about their use. This study aimed to address both doubts and questions by evaluating the effect of spraying rice using a canopy-opening device and a canopy-opening divider combination device. The tested rice variety was “Longliangyou 2010”. Three different boom sprayers were evaluated for this purpose: (1) a boom sprayer with a canopy-opening device, (2) a boom sprayer with a canopy-opening divider combination device, and (3) a traditional boom sprayer. The effects of the position of the canopy-opening device and the spraying velocity on the deposition of droplets were considered. The experiments showed that the droplet coverage was significantly affected by boom sprayers, the position of the canopy-opening device, the spraying velocity, and the interaction of the position of the canopy-opening device and the spraying velocity. Under the spraying distance of 60 cm from the rice root and the spraying velocity of 1.2 m s⁻¹, the spraying coverage of the paraxial surface of the whole canopy was higher than that of other treatment conditions when the canopy opening device was used. The positive spraying coverage rates of the upper, middle and lower layers were 95.18%, 88.41% and 94.99%, respectively. Compared with the traditional boom sprayer, the use of the canopy-opening device increased the average droplet coverage on the adaxial surface canopy by more than 72.91% and the average droplet coverage on the abaxial surface canopy by more than 6.88%.

1. Introduction

Rice plant protection operation is an important link in the process of rice management because pests and diseases occur throughout the rice lifespan. When spraying pesticides, the canopy structure has a great influence on the spread and retention of droplets [1,2]. Canopy volume and foliage density increase with rice growth. Spray droplets have less opportunity to reach the interior of the rice canopy and show a trend of attenuation layer by layer from top to bottom when spraying in the middle and late stages of rice growth due to the lush foliage and fewer pores in the rice canopy. The amount of spray droplet deposition in a dense canopy is 40% less than that in medium- and low-density canopies [3]. In this case, the overall deposition is extremely uneven and has a serious impact on the control of diseases and pests, further reducing rice yield. At the heading stage of rice, there are mainly diseases and pests such as rice blast and rice planthopper. Rice blast reduces global rice yield by 10–30% annually [4]. Rice planthoppers cause the most serious rice yield loss among global rice pests and diseases [5]. They occur mainly in the middle and lower layers of rice. Thus, implementing corresponding measures to enhance deposition uniformity and pesticide utilization has significant implications for rice production.

There are two main ways to increase the deposition of the lower part of the canopy: air-assisted spraying and canopy-opening spraying. Air-assisted spraying improved deposition or infiltration in crop canopies [6,7,8]. However, the cost of air-assisted sprayers is higher, and the use of large fans requires additional power [9]. Rice is planted in wetlands, and the wetland conditions limit the possibility to use air-assisted boom sprayers.

A canopy-opening device is an efficient, easily adjustable, inexpensive, and simple device that can improve the deposition or penetration in crop canopies [9,10]. The canopy-opening device usually consists of a conduit or pipe mounted on the spray boom in front of the nozzles. During spray operation, the canopy-opening device is in front of the spray area, and the upper canopy branches and leaves are moved to create the canopy space so that the droplets can smoothly enter the rice canopy and improve the deposition and distribution of droplets in the middle and lower canopies of the rice. Zhu et al. (2008b) studied the impact of the canopy-opening device on soybean plants, but the canopy-opening device they designed to come into contact with soybean plants was a rod [11]. If this canopy-opening device was applied to rice plants, it might increase the damage to rice. Additionally, the object of this research is only greenhouse crops, and the effect of the canopy-opening device when applied to rice remains to be verified. Wu et al. (2019) studied the mechanical interaction between the canopy-opening device and rice through computer simulation but did not apply it in practice. They only studied the impression of the position of the canopy-opening device on the displacement of the rice stem and did not consider that the spraying velocity is also an important parameter in actual use.

Divider devices can also create crop canopy space. During spray operation, the crops can be divided into two sides under the action of the divider device, which creates more space for spraying. For plant protection in the middle and late stages of crop growth, using a divider device can significantly improve the deposition of droplets in the middle and lower layers of the plant [12]. However, due to the problem of row spacing, the divider device cannot be used alone for rice crops. The canopy-opening device and the canopy-opening divider combination device are not widely applied to protect rice plants. At present, the canopy-opening device is only used in the laboratory and has not been popularized, because growers are still skeptical as to whether using the canopy-opening device and the canopy-opening divider combination device can improve the deposition of droplets in the middle and lower layers of rice. Therefore, to improve the viability of canopy-opening devices and canopy-opening divider combination device spraying, the accuracy of various parameter combinations and settings of the boom sprayer need to be carefully considered.

This study investigated spray deposition when using a boom sprayer with a canopy-opening device, a boom sprayer with a canopy-opening divider combination device, and a traditional boom sprayer. Three positions of each device and three spraying velocities were considered. The objective of the study was to obtain the best spray combination parameters by evaluating the effects of different spraying equipment, the position of the canopy-opening device and the spraying velocity on the droplet deposition.

2. Materials and Methods

2.1. Materials

The tested rice was “Longliangyou 2010”. Its growth period is the heading stage. The planting spacing, planting height, and leaf area index (LAI) were 10 × 18 cm², 0.8–1.2 m, and 8.7 m² m⁻².

2.2. Test Platform

The test platform was the Swan Group Essen SWAN3WP-500 boom sprayer. The length of a single spray boom was 5 m, and there were two spray booms in total. The spraying swath was 12 m. The spray boom was related to the frame through a parallelogram mechanism, and it lacked damping suspension. The height of the spray boom from the ground was adjustable between 0.46 m and 1.39 m through the double-acting oil cylinder. The pesticide storage tank capacity, engine power, and spraying velocity were 500 L, 17.1/3600 kW(PS)/rpm, and 0~11 km h⁻¹, respectively. Twelve conical nozzles were mounted on the whole spray boom. The nozzles were installed under the spray rod. The nozzle model, working pressure and flow were as follows: ARAG-422HCC035, 0.3~2 MPa, and 1.4~3.61 L/min. Nozzle spacing is 47 cm. The main parameters of the nozzle are presented in

Table 1. Characteristic parameters of the nozzle.

	Parameters
Position	Front
Nozzle model	ARAG-422HCC035
Pressure	0.3~2 MPa
Flow rate (one nozzle)	1.4~3.61 L/min
Nozzle spacing	47 cm
Number	12
Spraying angle	80° (vertically down)

. The SWAN3WP-500 boom sprayer was equipped with a GPS positioning system, which could display the spraying velocity in real time. The main parameters of the GPS are presented in

Table 2. Characteristic parameters of the GPS.

Performance Criteria.	Parameters
Signal	GPS L1/L2
Position accuracy (RMS)	1 cm + 1 ppm (parts per million)
Velocity accuracy (RMS)	0.03 m s−1
Time accuracy (RMS)	20 ns
Locator data refresh rate	20 Hz

.

Only one boom sprayer was used for the whole test to reduce the influence of other variables on the test. We added a canopy-opening device lifting system at the front of the sprayer and used hydraulic cylinders to control the up and down movement of the lifting device. The lifting system of the canopy-opening device is shown in Figure 1a. This study simply optimized the canopy-opening device to reduce the damage to rice plants. The actuator of the traditional canopy-opening device is a cylindrical rod, which has less contact area with rice. In order to reduce the possible damage to rice caused by the canopy-opening device, this study uses a bent rectangular iron plate as the actuator of the canopy-opening device, increasing the contact area between the canopy-opening device and rice. The 3D schematic drawing of the optimized canopy-opening device is shown in Figure 1b.

Based on the SWAN3WP-500 boom sprayer, the canopy-opening device was installed under the spray boom (Figure 2a). The total length of the canopy-opening device was 12 m. The height of the canopy-opening device from the ground was adjustable between 0.5 and 1.43 m. The spray booms were above the canopy-opening device and in front of the sprayer, behind the canopy-opening device. The vertical height of the spray boom from the canopy-opening device can be adjusted from 0 to 0.5 m, and the horizontal distance can be adjusted from 0 to 0.5 m (Figure 1b). Based on the boom sprayer with the canopy-opening device, the divider device was installed under the canopy-opening device (Figure 2b). The spacing, width, and height of the divider device were 30 cm, 15 cm, and 20 cm, respectively. The canopy-opening device and the divider device moved as a whole.

2.3. Test Design

2.3.1. Working Parameter Settings

An orthogonal experiment with three factors and three levels using SPSS v.20.0 software (SPSS Corporation, Chicago, IL, USA) was designed (

Table 3. Orthogonal experimental design.

Treatments	Spraying Equipment	Spraying Velocity (m s−1)	Height (m)
A	R1	V1	H1
B	R1	V2	H2
C	R1	V3	H3
D	R2	V2	H1
E	R2	V3	H1
F	R2	V1	H2
G	R2	V3	H2
H	R2	V1	H3
I	R2	V2	H3
J	R3	V1
K	R3	V2
L	R3	V3

) to evaluate the effects of different spraying equipment (R1, R2, and R3), spraying velocity (V1 = 0.8, V2 = 1.2, and V3 = 1.6 m s⁻¹), and the position of the canopy-opening device or canopy-opening divider combination device (H1 = 0.6, H2 = 0.7, and H3 = 0.8 m) on droplet deposition and coverage so as to reduce the test cost. Here, R1, R2, and R3 are, respectively, the boom sprayer with the canopy-opening divider combination device, the boom sprayer with the canopy-opening device, and the traditional boom sprayer. Since the traditional boom sprayer was not equipped with other devices, the spray bar was kept 40 cm higher than the rice canopy during the test.

2.3.2. Arrangement of the Sampling Point

The droplet penetration test was conducted in the Runguo agricultural experimental field in Jiangsu province. The spray test was conducted under windless or weak wind (wind velocity < 1.5 m s⁻¹) conditions. A water-sensitive paper (WSP, 25 × 75 mm²) was used as the sampling piece to receive the droplets [13]. WSP was placed on the adaxial and abaxial surfaces of each part, 70, 40, and 10 cm away from the ground, respectively (Figure 3), in which the transverse spacing (n = 4) and longitudinal spacing (n = 5) were 1 and 2 m, respectively. The spraying area for the droplet deposition distribution uniformity test is shown in Figure 4. The total number of sampling points was 20, and each point was collected repeatedly three times. The samples were collected after the droplets were completely dry. The WSP was carefully taken out with clean tweezers, and the recovered water-sensitive paper was marked and analyzed with image processing software [14].

2.4. Test Methods

2.4.1. Determination of Actual Droplet Diameter

Studies suggest that the volume median diameter of droplets had a critical impact in terms of reducing and effectively controlling the dosage [15]. The size of pesticide droplets directly changed the toxicity of pesticides to insects. The change in droplet size also affected the deposition density and deposition behavior of droplets on the target.

The equation to calculate the actual droplet diameter (ADD, μm) is shown in Equation (1) [14].

$$\mathrm{ADD}=\mathrm{b}\times {\left(\frac{4\mathrm{a}}{\mathsf{\pi }}\right)}^{\mathrm{c}\ast 0.5}$$

(1)

In Equation (1), a is the spot area (μm²) acquired from the image. b and c are constants for calculating the diffusion factor, which are automatically selected by the DepositScan according to the image contrast.

2.4.2. Droplet Coverage and Distribution Uniformity

The ratio of the number of droplet pixels covered by the analyzed droplet presented the coverage of the droplet on the water-sensitive paper [16], which was calculated using Equation (2).

$$\mathsf{\delta }=\frac{{{\displaystyle \sum }}_{\mathrm{i}=0}^{\mathrm{M}}{{\displaystyle \sum }}_{\mathrm{j}=0}^{\mathrm{N}}\mathrm{f}\left(\mathrm{i},\mathrm{j}\right)}{\mathrm{MN}}\times 100\%$$

(2)

In Equation (2), M and N represent the number of pixels in the width and length of the analysis area, respectively. f(i, j) is the value of the pixel at the relative coordinates of (i, j) in the binary images of the analysis area, respectively. If the pixel was black, then f (i, j) = 1; otherwise, f (i, j) = 0.

According to the numerical calculation results, the average values of droplet deposition (volume of target droplets) on the upper (0.7 m), middle (0.4 m), and lower (0.1 m) leaves of the plant target were counted (Figure 3). According to Equations (3)–(5), the coefficient of variation (CV) was calculated and CV was used to measure the uniformity of droplet distribution [17,18,19].

$$\overline{\mathrm{q}}=\frac{{\mathrm{q}}_1+{\mathrm{q}}_2+{\mathrm{q}}_3}{\mathrm{n}}=\frac{\sum \mathrm{q}}{\mathrm{n}}$$

(3)

In Equation (3), q₁, q₂, and q₃ are the droplet deposition per unit area of the upper-layer, middle-layer, and lower-layer blades (μL/cm²); $\overline{\mathrm{q}}$ is the average value of droplet deposition distribution (μL/cm²); and n is the sample size.

$$\mathrm{S}=\sqrt{\frac{\sum {\left(\mathrm{q}-\overline{\mathrm{q}}\right)}^2}{\mathrm{n}-1}}=\sqrt{\frac{\sum {\mathrm{q}}^2-\frac{{\left(\sum \mathrm{q}\right)}^2}{\mathrm{n}}}{\mathrm{n}-1}}$$

(4)

In Equation (4), S is the standard deviation of droplet deposition distribution.

$$\mathrm{CV}=\frac{\mathrm{S}}{\overline{\mathrm{q}}}\times 100\%$$

(5)

In Equation (5), CV is the ratio of the standard deviation to the average value of droplet deposition distribution.

2.5. Data Processing

In this field experiment, 1440 sediment measurements were carried out (12 experiments, 20 collection sites, and 6 different collection points). The model of WSP is 20301-1N. The Lenovo M7605D scanner was used to scan water-sensitive paper at 600 dpi. In addition to spray coverage (percentage of target covered), spray density (droplets cm⁻²), and liquid deposition ((µL cm⁻²) were also determined by DepositScan. The same device was also utilized to compare the droplet deposition impact of the canopy-opening device at different positions. All analyses were performed using SPSS v.20.0 software. The single-sample Kolmogorov–Smirnov (K-S) test was used to test the normal distribution of the droplet coverage and droplet deposition per unit area of WSP at different collection points. The data were subjected to factorial analysis of variance (ANOVA) to assess the influence of different research factors (boom sprayer, spraying velocity, and the position of canopy-opening device) on canopy deposition. Figure 5 shows an example of spraying results.

3. Results and Discussion

3.1. Analysis of Deposition Effect

After the K–S test was performed on the droplet coverage on the adaxial surface of the rice (Figure 6), it was found that the droplet coverage conformed to the normal distribution under the 95% significant condition (P = 0.18 > 0.05).

ANOVA showed that different boom sprayers had a significant effect on the droplet coverage on the front surface of rice leaves (F = 22.29, P < 0.05). Multiple comparison analysis using the least significant difference (LSD) method showed that the coverage provided by the boom sprayer with the canopy-opening device was significantly different from that provided by other boom sprayers. The position of the canopy-opening device had a significant effect on the droplet coverage on the adaxial surface of rice leaves (F = 5.28, P < 0.05). When the height of the canopy-opening device from the ground was 0.6 m, the droplet coverage was significantly different from other heights according to the LSD method. The spraying velocity had a significant effect on the droplet coverage on the adaxial surface of the rice leaves (F = 27.15, P < 0.05), and a significant difference was found between the velocity groups using the LSD method. Therefore, different boom sprayers, the position of the canopy-opening device, and the spraying velocity had different effects on the droplet coverage on the adaxial surface of the rice leaves.

Multivariate ANOVA on droplet coverage revealed an interaction between spraying velocity and the position of canopy-opening devices. The significance of the interaction between the two factors was 0.02, which was less than the significance level of 0.05. Therefore, an interaction was found between the position of the canopy-opening device and the spraying velocity, which had a significant impact on coverage.

3.2. Droplet Permeability

Table 4. Average droplet coverage under different treatments.

Average Droplet Coverage (%)	Layers	Treatments
		A	B	C	D	E	F	G	H	I	J	K	L
Adaxial surface	Upper	71.51	26.46	20.06	95.18	94.68	71.36	12.24	21.53	33.38	32.36	28.96	12
	Middle	42.55	12.78	13.57	88.41	34.21	66.79	8.56	13.47	13.12	15.08	13.4	5.04
	Under	20.32	17.27	14.44	94.99	51.94	55.29	7.13	22.94	11.57	12.41	8.95	5.06
Abaxial surface	Upper	0.36	0.75	1.67	13.59	9.47	1.12	0.24	1.08	1.37	0.39	0.13	0.22
	Middle	2.44	0.4	0.19	3.29	45.84	0.56	0.41	11.93	0.31	0.12	0.21	0.35
	Under	2.08	1.07	0.36	4.01	11.22	0.38	0.19	0.35	0.89	1.17	0.28	0.08

shows the differences between the spraying coverage of different boom sprayers, the position of the canopy-opening device, and the spraying velocity of different collectors. This gave a good idea about the spraying average depositions under different conditions and the relationship between them. All treatments showed much higher droplet coverage on the adaxial surface than on the abaxial surface. The adaxial surface droplet coverage of the rice canopy under D, E, and F treatments was much higher than under other treatments. The A, B, and C treatments showed that the droplet coverage of each canopy of rice showed a downward trend with the increase in the height and spraying velocity using the canopy-opening divider combination device. The J, K, and L treatments showed that the droplet coverage of each canopy of rice with the ordinary boom sprayer decreased with the increase in the spraying velocity. Under treatment D, the adaxial surface droplet coverage of the rice canopy was higher than under other treatments. The difference between treatment D and treatment I is only the height. The height of treatment G is higher than that of treatment E, and the height of treatment H is higher than that of treatment F, and the spraying velocity of both is the same. This shows that when the canopy-opening device is used, and when the height is 0.6 m, the droplet coverage rate of each canopy of rice is relatively large, and the coverage rate decreases with the increase in height. Compared with treatment E, treatment D has the same height, but the spray rate is lower than treatment E. Compared to treatment E, treatment D has the same height, but a lower spraying velocity. The same phenomenon is also observed when comparing F and G. However, the opposite phenomenon occurs in the comparison of H and I. Therefore, when the opening device is at the same position, the spraying velocity is 1.2 m s⁻¹, and the droplet coverage on the adaxial surface of each canopy has a better performance.

As shown in Figure 7, using the boom sprayer with the canopy-opening divider combination device at a lower spraying velocity (0.8 m s⁻¹) and lower position of the canopy-opening divider combination device (0.6 m) caused the deposition of a large number of droplets on the front side of the upper layer of rice. The ratio of droplet coverage of the middle and lower layers and the adaxial surface of the upper layer gradually decreased, but the spraying coverage of the abaxial surface of the upper layer gradually increased, with the increase in the spraying velocity and the position of the canopy-opening divider combination device.

The spraying coverage of the whole canopy adaxial surface under treatment A was higher than that under treatments B and C. The spraying coverage of the upper adaxial surface under treatments A, B, and C was 71.51%, 26.46%, and 20.06%, respectively. The spraying coverage of the adaxial surface of the middle and lower layers was much lower than that of the upper layer due to the interference of rice height and the leaf area index. Under treatments A, B, and C, the adaxial surface spraying coverage of the middle layer was 42.55%, 12.78%, and 13.57%, respectively, and the adaxial surface spraying coverage of the lower layer was 20.32%, 17.27%, and 14.44%, respectively. This result emerged from the belief that the canopy-opening divider combination device could help open the dense canopy of rice while the applicator was running, allowing more droplets to pass through the upper canopy to the lower layer.

Under the condition of treatment A, the spraying coverage on the abaxial surface of the middle and lower layers reached the maximum, which was 2.44% and 2.08%, respectively. Under the C treatment, the spraying coverage on the abaxial surface of the upper layer was the highest, reaching 1.67%. This result might be due to the stronger disturbance of the upper canopy thanks to the higher position of the canopy-opening divider combination device, meaning that more droplets were deposited on the abaxial leaf surface of the upper layer of rice.

As shown in Figure 8, using the boom sprayer with the canopy-opening device at the middle spraying velocity (1.2 m s⁻¹) and the lower position of the canopy-opening device (0.6 m) can cause the deposition of a large number of droplets on all layers of rice. The ratio of droplet coverage of the full canopy of rice showed a decreasing trend with the increase/decrease in the spraying velocity and the increase in the position of the canopy-opening device. Under the D treatment condition, the spraying coverage of the adaxial surface on the entire canopy was higher than that under the other treatment conditions. The frontal spraying coverage of the upper, middle, and lower layers was 95.18%, 88.41%, and 94.99%, respectively.

Under the condition of E treatment, the spraying coverage on the abaxial surface of the middle and lower leaves reached the maximum, which was 45.84% and 11.22%, respectively. Under the condition of D treatment, the spraying coverage on the upper and abaxial surfaces of rice leaves was the highest, reaching 13.59%. This was probably because, under the condition of the lower position of the canopy-opening device, the number of pores in the upper canopy increased with the increase in the spraying velocity. Therefore, more droplets penetrated the upper canopy and were deposited on the abaxial surface of the middle canopy.

As shown in Figure 9, the traditional boom sprayer had a high spraying coverage at a low spraying velocity (0.8 m s⁻¹). The ratio of droplet coverage of the adaxial surface of rice showed a downward trend with the increase in the spraying velocity, whereas the spraying coverage on the abaxial surface of the middle layer showed an upward trend, reaching 0.35%.

Overall, the combination of the canopy-opening device and the divider device did not achieve better results. Compared with the traditional boom sprayer, the use of the canopy-opening device increased the average droplet coverage on the adaxial surface canopy by more than 72.91% and the average droplet coverage on the abaxial surface canopy by more than 6.88%. This result showed that the use of the canopy-opening device significantly improved the spraying coverage in the entire canopy of rice.

3.3. Droplet Distribution Uniformity

The deposition amount of pesticide droplets is the premise for effectively controlling pests and diseases. The control effect is directly related to the uniform deposition and distribution of droplets on the plant [20]. The CV was introduced as the evaluation index of droplet deposition and distribution uniformity in the plant canopy to verify the deposition effect of different boom sprayers on droplets in the middle and lower layers of the canopy. The smaller the value, the better the deposition uniformity of the droplets in each layer.

The percent stacked column chart of Figure 10 shows the proportion of average deposition of different canopy layers under different experimental treatments. The treatment conditions with the highest distribution of droplet deposition in the upper, middle, and lower layers of rice plants were K, A, and D, which were 77%, 45%, and 34%, respectively. It can be seen from the figure that the distribution of canopy deposition under D and H treatments is more uniform. The droplet distribution of the upper, middle and lower layers under treatment D is 34%, 30% and 36%, respectively. The droplet distribution of the upper, middle and lower layers under treatment E is 32%, 36% and 32%, respectively. The droplet distribution of other treatments is not as uniform as that of treatments D and E.

The line graph in Figure 11 shows the average droplet deposition in different rice canopy layers under different treatments. Figure 10 shows that the rice canopy deposition under the DEF treatment is much higher than that under other treatments. It can be clearly seen from Figure 11 that under treatment D, the sediment amount in the rice canopy is higher than that of other treatments. The difference between treatment D and treatment I is height. The height of treatment D is H1 and that of treatment I is H3. The height of treatment G is higher than that of treatment E, and the height of treatment H is higher than that of treatment F. Additionally, their spraying velocity is the same. This shows that when the canopy-opening device is used, when the height is 0.6 m, there will be more canopy deposition, and the higher the height is, the less the deposition. Compared with treatment E, treatment D has the same height, but the spraying velocity is lower than that of treatment E. Compared with treatment E, treatment D has the same height, but the spraying velocity is smaller. Treatments F and G and treatments H and I have the same phenomenon after comparison. Therefore, when the canopy-opening device is in the same position, the slower the spraying velocity is, the higher the dosage is.

Figure 12 shows the CV of droplet deposition under different experimental treatments. Under the treatment of D, E, F and H, the coefficient of variation of droplet deposition is small, showing relatively uniform droplet deposition. These treatments all use canopy-opening devices. However, only D had the most uniform droplet deposition distribution, and the CV under D treatment was 2.9%. Therefore, the boom sprayer with the canopy-opening device improved the uniformity of droplet deposition in the whole canopy of the rice plant, which was more conducive to the control effect of diseases and pests in the middle and lower layers of the rice plant.

4. Conclusions

In conclusion, the comparison of the spraying test of different boom sprayers under different conditions showed that the combination of the canopy-opening device and the divider device did not achieve the ideal application effect, but was better than the traditional boom sprayer. The boom sprayer with the canopy-opening device showed the ideal spraying coverage and droplet deposition, and the droplet spray deposition distribution was the most uniform. This result is consistent with Zhu et al. (2008b)’s research.

Different canopy-opening positions and spraying velocities and their interactions had significant effects on the spraying coverage. Using the boom sprayer with the canopy-opening device at the spraying velocity of 1.2 m s⁻¹ and the position of the canopy-opening device being 0.6 m caused the ideal spray effect. This is similar to Wu et al. (2019)’s conclusion: when the canopy-opening device was located at the middle level of the rice canopy, optimal displacement was obtained. However, the spraying coverage of the full canopy of rice showed a decreasing trend with the increase/decrease in the spraying velocity and the increase in the position of the canopy-opening device.

The canopy-opening device could open the dense canopy of rice so that more droplets were deposited in the middle and lower layers of the rice plant, but we could only study the rice plant at the heading date. In practical applications, the depth of the canopy-opening device should be adjusted according to the different densities of rice.