Design and Experimentation of an Aerial Seeding System for Rapeseed Based on an Air-Assisted Centralized Metering Device and a Multi-Rotor Crop Protection UAV

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An aerial seeding system for rapeseed based on an air-assisted centralized metering device and a commercialized multi-rotor crop protection UAV (unmanned aerial vehicle) is presented.

Abstract

To improve the overall mechanization level of rapeseed production in China, especially in some hilly regions where ground machinery cannot enter the fields or can only enter with very low economic benefits, a special aerial seeding system for rapeseed based on a miniature air-assisted centralized metering device was designed and tested in this study. Unlike existing commercial aerial seeding systems, the proposed seed meter was a miniaturized version derived from the traditional air-feeding seed meter on ground planters. The new version contained a redesigned seed feeding component to overcome problems of serious air backflow to the seed box and difficult seed feeding after miniaturization. Three groups of experiments were designed and conducted to optimize the parameters of the seed meter and test its performance. Results from the orthogonal experiment showed that the seed feeding component performed best when the seed layer thickness was 45 mm, the rotational speed of the gear disc was 45 r/min, and the airflow pressure was 2450 Pa. Results from the static workbench test showed that the designed seeding system had a maximum average total sowing efficiency of 537.17 g/min, with the maximum values of the stability variation coefficient of total seeding rate (seven ports) and the consistency variation coefficient between each port was 2.37% and 4.89%, respectively. Field tests further proved that the designed aerial seeding system could work stably, uniformly, and efficiently, so that the agronomic requirements of rape crop planting could be well met.

1. Introduction

Rapeseed is one of the most important oil crops in the world. Aside from its oil crop function, it is also planted as important production sources of honey, forage, and manure and as tourist attractions [1]. Its multi-function application attributes determine that it is planted in different regions of China from plains to hills and from river valleys to shore fields. This situation also leads to a diversity of rapeseed planting methods including direct seeding and transplanting by manual labor, direct seeding and transplanting by ground machines, and direct seeding by aerial vehicles. Overall, the current mechanization level of rapeseed seeding in China is still quite low, far below grain crops such as wheat, rice, and corn. To exploit the multi-function application potential of rapeseed, increase the growers’ income, and strengthen their enthusiasm to keep on planting it, there is an urgent need to raise the mechanization level of rapeseed planting in China to save production costs.

Near-ground aerial seeding is a seeding method worth studying. Since the field surface is not touched while the unmanned aerial vehicle (UAV) works at high speeds, it can work in fields of different terrain conditions [2,3,4]. Aerial seeding would be a beneficial method supplementary to ground planting, providing a solution for rapeseed planting in regions where ground machines cannot enter or can only enter with very low economic efficiency. Furthermore, the fact that rape seeds are small and can germinate and grow easily after being spread to the soil surface increases the potential of applying aerial seeding.

European and American countries have a long history of aerial seeding, especially for cover crops grown in forests and prairies, and the operation is usually done by manned helicopters or fixed-wing aircraft platforms [4,5]. These kinds of equipment are large and expensive, and the seed landing spots are not accurately controlled. These features make them unsuitable for use in small-size fields, which are very common in southern China. In recent years, with the continuous advancement of technologies such as positioning and navigation, battery, and flight control, the application of small multi-rotor UAVs is developing rapidly, and they have been applied successfully in agricultural operations including remote sensing, mapping, and plant protection [6,7,8].

Some tech companies in China have started adding aerial seeding capabilities into their agricultural UAVs to make them more versatile and acceptable. Enterprises such as Zhuhai Yuren, Shenzhen D.J. [9], and Guangzhou X.A.G. [10] have added spreading devices or systems for granular materials to their commercial UAVs to expand their aircrafts’ functions rather than plant protection only. The spreading system of DJ and some other enterprises adopted a centrifugal-disc seeder that was first proposed by Li et al. [11] from South China Agricultural University. Then, the XAG JetSeedTM spreading system and the system reported in Song et al. [12] utilized an external grooved wheel seeder to quantify seed supply and a ducted fan to accelerate the seeds’ movement. Huang et al. [13] from Huazhong Agricultural University proposed a special centrifugal seeding system based on an XAG P20 UAV. The system could realize seeding rape seeds in lines with the help of a specially designed seed guiding tube. However, the tube was required to be manually hitched to the UAV by a person when the UAV was hovering, which posed an operational risk.

Unlike the above aerial seeding systems, the aerial seeding system in this study was based on a miniature air-assisted centralized seed meter adopted from a ground rapeseed planter [14]. However, the seed meter was redesigned to fit a six-rotor UAV’s structure and dimensions, especially on the seed feeding component to overcome problems of serious air backflow and difficult seed feeding after miniaturization. The main contributions of this study are summarized as follows: (1) an aerial seeding system for rapeseed based on a miniature air-assisted centralized meter was designed, with its main parameters determined to fit a multi-rotor agricultural UAV; and (2) the performance of the aerial seeding system was tested and evaluated in workbench experiments and field experiments, based on which a new aerial seeding solution for rapeseed was proposed.

The remainder of this paper is organized as follows. The overall structure and working principle of the rapeseed seeding system with its key components are introduced in Section 2. Then, three experiments including a standard orthogonal experiment, a static workbench experiment, and a practical field experiment are introduced in Section 3. Results and discussions are presented in Section 4. The conclusions are drawn in Section 5.

2. Design of Structure and Main Parameters

2.1. Agronomic Requirements for Rapeseed Sowing

Winter rapeseed (Brassica napus L.) is widely cultivated in China, especially in the middle and lower reaches of the Yangtze River. This crop is sensitive to season conditions, especially temperature, when sowing. In winter rapeseed growing regions, a suitable temperature for the seeds to germinate is 16~22 °C. Therefore, the sowing operation generally occurs from late September to mid-October, no later than the end of October. It is best to sow the rapeseed in the morning one day before or after a rain. The seed sowing amount is about 6 kg/hm², and the population density of rape seedlings is about 2.0~6.0 × 10⁵ per hm² [15].

In aerial seeding, the field soil is not touched by the machine, and unlike ground seeding, there are no ditching and soil covering processes. To ensure enough germination, three operation modes of aerial seeding for rapeseed are usually utilized in practice [13]: (i) aerial seeding after tillage with a rotary tiller, in which the seeds can fall into the gaps between soil clods; (ii) aerial seeding without any field treatment, and then covering the seeds with soil from trenching by a ground trencher or just by manual labor; and (iii) aerial seeding without any ground operation, only increasing sowing density to ensure enough seedlings per area. In addition, if the previous crop is rice, it would be best to carry out aerial seeding 2–3 days before the rice is harvested. The seeds are more likely to be covered by crushed rice straws and soil after rice harvesting, and can then germinate more easily due to better surface moisture.

2.2. Overall Structure and Working Principle

A commercial six-rotor agricultural UAV (model: 3WDM6-10, Lockheed Co. Ltd., Wuhan, China) was selected as the seeding platform. After removing the original spraying module, we added the aerial seeding system. The whole hardware structure with the air-assisted centralized metering device is shown in Figure 1. The whole system is composed of three main modules: aircraft, seed supply module, and seed distributing and guiding module. The seed supply module is used to get seeds from the seed box at a preset seed flow rate and deliver them to the distributor via airflow from the fan. The seeds are accelerated under the airflow and divided into several rows by the distributor. In each row, seeds proceed to move through the hose and hard tube, and then they drop from the seeding tube toward the field.

Removing the aircraft platform, the remaining seeding system can be seen as a scaled-down version derived from a traditional air-feeding seeding system on a ground planter designed by Lei et al. [14]. However, the whole system was redesigned to match the aircraft’s structure and operating characteristics. In particular, a new seed feeding component was built to overcome the problems of serious air backflow and difficult seed feeding after miniaturization. The aircraft wheelbase (the distance between two motors at opposite corners) is about 1.2 m, so the width of the seeding device was designed to be about 1.8 m with seven seed outlets. Correspondingly, the working width of the aerial seeding system was 2.1 m. The nominal maximum takeoff weight of the aircraft was 20 kg, and the nominal maximum working speed was 8 m/s. The net weight of the aerial seeding device was about 3 kg, and the UAV could carry about 5 kg rape seeds at a time.

2.3. Seed Feeding Component

The seed feeding component is a key component that affects the stability of seed discharge [16,17,18]. As shown in Figure 2, the redesigned seed feeding component in this aerial seeding system consists of a seed filling chamber, a seed gear disc, and a seed delivery tube. Seeds drop from the seed box to the seed filling chamber via gravity, proceed to fill into the gaps between adjacent racks of the gear disc, and form a seed layer. The seed feeding motor rotates the gear disc and pushes the seeds into the vertical channel of the seed delivery tube. The seeds falling into the channel are carried upwards into the distributor by the airflow generated by the fan.

The process can be divided into four steps: seed filling, seed carrying, seed cleaning, and seed dropping. The seed gear disc not only transfers the seeds from the chamber to the vertical tube continuously and quantitatively, but also prevents the airflow from going back to the chamber and seed box.

To guarantee the number of seeds per unit area, more seeds should be sown when the UAV works at a higher flying speed, and a higher rotational speed of the gear disc/seed feeding motor should be set. A formula was used to calculate the seeding quantity as follows:

$$G_Y\ge \frac{GB{V}_f}{10}$$

(1)

where G_Y is the seeding quantity per second (g/s); G is the quantity of seeds per unit area according to the agronomic requirements (kg/hm²); B is the working width of the aerial seeding system (m); and V_f is the flying speed of the UAV (m/s).

According to the agronomic requirements introduced in Section 2.1, G is 6 kg/hm², since B is 2.1 m, and if we choose V_f to be 5 m/s, then we get G_Y ≥ 6.35 g/s. This means that the seed feeding component should deliver 6.35 g seeds per second or 381.00 g per minute at least.

To calculate the seed feeding quantity according to the structure parameters of the gear disc and the rotational speed of the feeding motor, we proposed another formula as follows:

$$G_S=\rho t\left[\pi \left(R^2-r^2\right)-Zh\left(R-r\right)\right]N/(6\times {10}^7)\ge G_Y$$

(2)

where G_S is the theoretical seed feeding quantity per second; N is the rotational speed of the gear disc; ρ is the density of the seed bulk; π is the mathematical constant Pi; t is the thickness of the gear disc; Z is the number of racks or gaps; and R, r, and h are the structure parameters as shown in Figure 2.

A small-size, lightweight but high-torque digital servo motor (model: LX224, Hiwonder Co. Ltd., Shenzhen, China) was chosen as the feeding motor. This is a serial bus servo motor that can work continuously and stably at 25 ~ 45 r/min with a torque range of 15 ~ 20 kg·cm. We chose N as 35 r/min for the average speed. The measured seed bulk density ρ was 674.5 kg/m³ [19]. Considering the structure strength, installation space limitation, and air tightness requirements, we set h = 2 mm, Z = 15, R = 35 mm, and r = 20 mm, then we found t ≥ 7.54 mm, which means that the gear disc thickness should be 7.54 mm at least and was rounded up to 8 mm at last.

2.4. Distributor and Fan

After seeds are sent to the vertical tube, the airflow has an important role to carry and make them move along the channel until they are blown out of the system and drop to the field. In the process of moving upwards to the distributor, the airflow should overcome the gravity of the seeds and the resistance force along the channel path. According to the particle suspension speed theory, the airflow speed to blow rape seeds upwards should be at least 6–7.5 m/s [20]. Considering the load and volume restrictions of the aircraft, a small but powerful fan (model: WS9250-24-240-X200, Wonsmart Co. Ltd., Ningbo, China) was chosen as the main power source of airflow, which needs a work voltage of 24 V DC with a 6.5 A current. Weighing 400 g, it can generate 42 m³/h airflow and 8 kPa air pressure in nominal.

The function of the distributor is to split the single seed stream into multiple strands equally via the airflow. A small-scale distributor with seven channels was designed as shown in Figure 3, according to the conventional air assisted centralized metering device of the ground planter. This was fabricated by 3D printing based on FDM (Fused deposition modeling) with PLA material.

3. Experiments

To test the performance of the aerial seeding system, three experiments were designed and carried out following a step by step procedure. The rapeseed variety used in the experiments was “Huayouza-62”, a winter Brassica napus variety developed by researchers at Huazhong Agricultural University in 2011 and is now widely planted in central China.

The first experiment was an orthogonal experiment [21]. The aim was to investigate how the performance of the seed feeding component was influenced by the main working parameters and to obtain the best combination of parameter values. The three factors considered in the experiment were the thickness of the seed layer, the rotational speed of the gear disc, and the air pressure of the fan. For each factor, three levels were set as shown in

Table 1. Factors and levels of the orthogonal experiment.

Factor Level	Seed Layer Thickness (mm)	Rotational Speed (r/min)	Air Pressure (Pa)
1	15	25	1960
2	30	35	2450
3	45	45	2940

. According to the orthogonal experimental design method [22], assuming that the influences of the three factors were independent, an L9 (3⁴) experimental plan was chosen (L9 (3⁴) stands for a standard orthogonal experiment of nine tests in total, four influencing factors, and three levels for each factor). For each level, three tests were carried out, and for each test, the seeding system worked for 1 min.

The second experiment was a static workbench test of the aerial seeding system. Figure 4 shows the setup of the experiment. The aim was to obtain the performance indexes while fixing the values of unimportant factors and varying the values of the most important one from the first experiment. The definitions of the performance indexes [14] are given as follows:

The stability variation coefficient of the total seeding rate C_VT is calculated by the following formula.

$$C_{VT}=\frac{{\sigma }_T}{{\mu }_{xT}}\times 100\%$$

(3)

where σ_T and μ_xT are the standard deviation and average value of the total seeding rate, respectively.

The consistency variation coefficient of the sowing quantity between each port C_VE is calculated by the following formula.

$$C_{VE}=\frac{{\sigma }_E}{{\mu }_{xE}}\times 100\%$$

(4)

where σ_E and μ_xE are respectively the standard deviation and the average value of the seeding rate between each port.

To further test the performance of the aerial seeding system in practice, a field experiment was carried out on 10 October 2019 on the outskirts of Maqiao Town, Xianning City, Hubei Province. Since the test fields for the UAV to fly on were surrounded with overhead power lines, ditches and ridges, and the sizes of the fields were small, to ensure absolute safety, a conservative test plan was adopted in which the flying speed was restricted to 4 m/s. Through a preliminary trial using mud boxes on the ground, the flying height was determined at 2 m for the designed working width B = 2.1 m. The natural wind force was smaller than level 2 during the experiment.

Given the quantity of seeds per unit area G = 6 kg/hm², the working width B = 2.1 m, and the flying speed V = 4 m/s, the corresponding seeding quantity per second G_Y was calculated to be 5.04 g/s using Equation (1). Then, a preliminary static workbench trial was conducted to determine the rotational speed of the gear disc.

To compare the performance, the seeding operation was also performed using another two systems: one was a ground planter Weiye 2BFG-4 from Hunan Province and one was an aerial seeding system based on an XAG P20 UAV. The second aerial seeding system was also developed by our team and some results have been published in [13]. Figure 5 shows the processes of the three systems in the field operation.

Both aerial seeding operations were conducted under the first operation mode (see Section 2.1), in which the field was lightly tilled by the rotary tiller on the ground planter without seeding. For all three seeding operations, subsequent investigations were conducted including counting seed germination rate on 10 November 2019 (30 days after seeding), monitoring seedling growing status in later months, and calculating yields and counting stubbles after harvesting on 10 May 2020. Figure 6 shows pictures taken during subsequent investigation processes. The yield and the stubble number for an area of 1 m² were calculated for comparison with the ground planter and the other aerial seeding system.

4. Results and Discussion

4.1. Standard Orthogonal Experiment

The L9 (3⁴) experimental plan and the corresponding results are shown in

Table 2. Results of the standard orthogonal experiment.

Test Number	A/Seed Layer Thickness	B/Rotational Speed	C/Fan Air Pressure	D/Blank Column	Seed Feeding Rate (g/min)
1	1(15)	1(25)	1(1960)	1	355.90
2	1	2(35)	2(2450)	2	352.00
3	1	3(45)	3(2940)	3	501.30
4	2(30)	1	2	3	359.70
5	2	2	3	1	345.30
6	2	3	1	2	478.30
7	3(45)	1	3	2	326.50
8	3	2	1	3	354.70
9	3	3	2	1	547.80
k1	403.07	347.37	396.30	416.33
k2	394.43	350.67	419.83	385.60
k3	409.67	509.13	391.03	405.23
Range	15.23	161.77	28.80	30.73
Ranking	B D C A
Optimal parameters	B3 C2A3

.

We can rank the importance of influencing factors by comparing the calculated ranges of all the factors. From Table 2, the range of factor B, the rotational speed of the gear disc, was much larger than that of A and C, which indicates that the rotational speed of the gear disc was the most important factor. Factor D was a blank factor and was treated as random errors. Since we have D > C > A and B > (C + A + D), we can treat the influences of seed layer thickness and fan air pressure also as errors. It should be noted that the three level values we set for each factor in the orthogonal experiment were within the normal operational limits. Only when the parameter values are within the limits can the influences of factors A and C be treated as errors. From Table 2, the combination of factor levels that output the best seeding performance was B₃C₂A₃ (i.e., the seed layer thickness was 45 mm, the rotational speed of the gear disc was 45 r/min, and the fan air pressure was 2450 Pa).

4.2. Static Workbench Experiment

The stability variation coefficient of total sowing quantity and the consistency variation coefficient of sowing quantity between each port are the two most important indicators to evaluate the performance of the centralized seeding system. In the static workbench test, the values of the two less important factors were fixed, in other words, the fan air pressure was set to 2450 Pa, and the seed layer thickness was set to 45 mm. The value of the most important factor (i.e., the rotational speed of the gear disc) was set to five levels (25, 30, 35, 40, 45) r/min. The relationship between the total sowing quantity and the rotational speed was studied, and the results are shown in

Table 3. Effect of rotational speed on seed metering performance.

Seeding Rotational Speed (r/min)	Seeding Rate of Each Port (g/min)								Total Seeding Rate (the Sum of Seven Ports) (g/min)	Stability Variation Coefficient of Total Seeding Rate CVT (%)	Consistency Variation Coefficient of Seeding Rate between each Port CVE (%)
	Test No.	Port 1	Port 2	Port 3	Port 4	Port 5	Port 6	Port 7
25	1	44.10	45.70	46.70	49.10	46.30	45.50	47.20	324.60	2.37	2.83
	2	43.80	39.80	45.30	46.10	43.20	46.20	45.20	309.60
	3	42.90	45.40	44.80	45.70	47.40	44.90	46.80	317.90
	Average	43.60	43.63	45.60	46.97	45.63	45.53	46.40	317.37
30	1	48.50	46.70	49.30	47.60	43.30	48.30	47.20	330.90	1.00	2.38
	2	45.70	48.90	49.70	43.50	47.60	46.10	43.80	325.30
	3	46.50	46.70	47.40	49.70	46.20	48.70	45.90	331.10
	Average	46.90	47.43	48.80	46.93	45.70	47.70	45.63	329.10
35	1	54.80	58.60	52.90	59.40	54.70	51.60	53.80	385.80	1.85	4.89
	2	52.10	56.20	51.20	56.40	51.40	49.80	54.70	371.80
	3	53.00	54.90	53.80	57.40	52.60	48.60	57.60	377.90
	Average	53.30	56.57	52.63	57.73	52.90	50.00	55.37	378.50
40	1	63.80	67.40	68.20	66.30	67.90	64.50	66.10	464.20	0.87	2.44
	2	62.10	66.90	67.80	63.80	64.70	63.60	68.40	457.30
	3	63.90	68.10	65.40	67.60	66.30	65.20	67.80	464.30
	Average	63.27	67.47	67.13	65.90	66.30	64.43	67.43	461.93
45	1	72.30	71.30	81.20	79.60	79.60	82.10	72.50	538.60	0.56	3.93
	2	74.80	73.90	79.10	79.40	76.80	80.70	74.50	539.20
	3	74.90	74.10	77.90	78.60	78.10	76.30	73.80	533.70
	Average	74.00	73.10	79.40	79.20	78.17	79.70	73.60	537.17

and Figure 7.

It can be seen from Table 3 and Figure 7 that:

(i)

The maximum average total seeding rate was 537.17 g/min when the rotational speed of the gear disc was 45 r/min, equivalent to 8.95 g/s, which indicated that the agronomic requirement of quantity of seeds per unit area could be met when the flying speed of the aircraft is 7.11 m/s theoretically.

(ii)

Both the stability variation coefficient of the total seeding rate and the consistency variation coefficient of the seeding rate between each port were very low, with the maximum values being 2.37% and 4.89%, respectively. This means that the system can ensure stability and uniformity in both the total seeding rate and the seeding rate of individual ports.

(iii)

The total seeding rate Y (g/min) increased with the rotational speed of the gear disc X (r/min) according to a polynomial fitting Y = 0.46014X² − 20.7614X + 544.78086 with R² = 0.9934.

4.3. Field Experiment

Since the flying height of the UAV influences the falling and final landing of the seeds to a large extent, before the formal field experiment, we performed a trial seeding test in which several mud boxes were placed on the ground to collect the seeds, and the seed landing effects of different flying heights were compared. Through the trial, the proper flying height was determined to be 1 m. Then, the formal field experiment of the aerial seeding operation process was conducted in the autonomous operation mode in which the working width was 2.1 m, the flying work speed was 4 m/s, the rotation speed of gear disc was 25 r/min, the seed layer height was 45 mm, and the wind pressure was 2450 Pa, which was compared to another two seeding modes. They used roughly equivalent seed quantity per hectare with the same kind of rape seed and field management.

After seeding, further investigations were followed including counting the seed germination rate after 30 days, monitoring seedling growth situation in later months, and calculating yields and counting stubble after harvesting. The results of the yields and the crop stubble numbers by three different seeding systems are shown in

Table 4. Yield investigation and stubble counting results.

Seeding Mode No.	Seeding System	Area (m2)	Yield (kg)	Estimated Average Yield (kg/hm2)	Crop Stubble Number per Square Meter N1	Estimated Average Crop Number per Hectare N2
1	Aerial seeding system in this study	997.4	168.3	1409.56	46.0 ± 7.2	4.19 × 105 × (1 ± 14.1%)
2	Aerial seeding system in study [13]	986.0	165.9	1338.54	42.7 ± 6.8	3.84 × 105 × (1 ± 14.4%)
3	Ground planter (Weiye 2BFG-4)	928.0	135.15	1192.13	45.5 ± 7.8	4.10 × 105 × (1 ± 15.4%)

. The average crop number per hectare N₂ was estimated by proportionally enlarging the crop stubble number per square meter N₁ and removing the gutter area by multiplying a coefficient of 0.9, that’s N₂ = N₁ × 10⁴ × 0.9.

From the data in Table 4, we found that:

(i)

The area of fields tested for three different systems were similar from 928.0 m² to 997.4 m² with corresponding yields of 135.15 kg to 168.3 kg.

(ii)

Further calculations resulted in estimated average yields from 1192.13 to 1409.56 kg/hm², in which the first mode had a slightly superior performance (5.30% and 18.24% greater) to the other two modes. The yields of all three modes were lower than the normal value in general for this rape variety of Huayouza-62. This might be due to some uncertain common problems in the field management and the relatively low soil fertility of the original fields.

(iii)

Average crop numbers per hectare, which was estimated by converting the stubble number while removing the area of the drainage ditch, were equal within error and met the agronomic technical requirements of seedling number per hectare. The first mode had the highest value of crop number and the best average yield. The second mode had the smallest value but the second average yield. The third mode had the second value of crop number, but the worst average yield. Two factors might be the cause of the above results. One would be the counting errors and sampling spot differences. The other might be the differences in soil fertility between fields.

5. Conclusions

A special aerial seeding system for rapeseed based on a miniature air-assisted centralized metering device was proposed. The system was designed and tested based on a commercial six-rotor plant protection UAV from Lockheed Co. Ltd. In the field tests, it was compared with two other rape seeding modes based on systems including a ground planter of Weiye 2BFG-4 from Hunan Province and another aerial seeding system with XAG P20 UAV. The main research conclusions are presented as follows:

(i)

The designed aerial seeding system could work stably, uniformly, and efficiently, well meeting the agronomic requirements of rapeseed planting. It resulted in an equivalent average yield and crop numbers per hectare compared with the other two seeding modes.

(ii)

Results from the standard orthogonal experiment showed that the rotational speed of the gear disc was the main influencing factor, followed by the fan air pressure, and the seed layer thickness. The best combination of parameter levels for the seed filling effect was B₃A₃C₂ (i.e., the seed layer thickness was 45 mm, the rotation speed was 45 r/min, and the fan air pressure was 2450 Pa).

(iii)

Both the stability variation coefficients of the total seeding rate and the consistency variation coefficient of the seeding rate between each port were very low, with the maximum value being 2.37% and 4.89%, respectively. The total seeding rate Y (g/min) increased with the rotational speed of the gear disc X (r/min) according to a polynomial fitting relationship Y = 0.46014X² − 20.7614X + 544.78086 with R² = 0.9934.

6. Patent

Huang, X.; Liao, Y.; et al. An aerial seeding method based on an air-assisted centralized metering device. Chinese Patent ZL2019104896088, 2019-06-06.