An Integrated Potato-Planting Machine with Full-Film Mulching and Ridged Row Soil Covering

Abstract

This paper presents the design of an integrated potato-planting machine capable of full-film covering, creating micro-ditches on ridges, and covering seed rows with soil. The machine addresses the challenges of traditional methods, allowing for mechanized planting with complete film coverage and individual seed row soil covering. The key components of the prototype were analyzed and designed. This includes the seeding system, the pointed wing-shaped trencher for creating micro-ditches, and the straddling film-mulching device. Additionally, the operating mechanism of these core components was analyzed. Field trials demonstrated an 85% success rate for seed depth placement under the film. The machine also achieved a 90% qualified index for seed potato spacing, with a 6% repetitive seeding rate and a 3% missed seeding rate. Furthermore, the qualified rate for covered soil width on seed rows was 94%, and the qualified rate for covered soil thickness was 93%. The adjacent row spacing achieved an 88% success rate. The degree of mechanical damage to the exposed surface of the mulch film was minimal, at only 30.2 mm²/m². These results meet all the national and industry standards. The successful field trials confirm the effectiveness of the machine in performing integrated fertilization, sowing, ridging, full-film covering, and seed row soil covering. Compared to traditional methods, this machine significantly reduces labor intensity for farmers and enhances the economic value of potato planting.

1. Introduction

In China’s northwestern dry zone, ridge cultivation with plastic film mulching has become the dominant method for potato farming [1]. This approach typically involves two main techniques: (a) Sowing first, then covering with film, where seedlings are manually released after emergence, a labor-intensive process with the risk of seedling burn due to high temperatures if not released promptly [2]. (b) Mulching first, then sowing on film, which requires specialized film-seeding equipment. Existing handheld punchers suffer, however, from low efficiency, poorly sealed holes that contribute to moisture loss, and the inability to handle potatoes’ inherent ability to break through the film [2,3,4].

Studies have shown that potato shoots can naturally penetrate the film [3,4]. Therefore, following film sowing, covering the seeds with a 30–50 mm soil layer is crucial. This ensures darkness for the germinating buds, preventing cotyledon separation, and relying on natural forces—the upward growth of shoots and soil pressure—to achieve seedling emergence without manual intervention [5]. As a result, potato full-film coverage technology has become a significant advancement in crop planting [6,7,8].

Current practices for film mulching rely on simple machinery and manual labor, leading to low efficiency and inconsistent quality. Insufficient soil cover exposes the film to wind damage, causing misalignment and seedling burns. Addressing these challenges is critical for the wider adoption of this technology.

Therefore, developing a machine that integrates full-film mulching, micro-groove creation on ridges, and seed row mulching, all aligned with dry-crop potato-planting agronomic standards, is essential for improving potato yields.

Since the 1950s, developed countries like Germany, Britain, the United States, and Canada have leveraged their strong theoretical foundation and technical expertise to continuously improve potato-planting technology. As a result, potato-planting machines have evolved significantly, from small, single-function machines to large, multi-functional, highly automated equipment. This advancement has led to significant improvements in production efficiency and seeding quality, with reductions in reseeding rates, leakage rates, and seed potato damage. Foreign potato-planting machinery can be broadly categorized into large-/medium-sized and small models. Some notable examples of large-/medium-sized machines include the following:

GL860Compacta (cup-type): An eight-row potato planter by Grimme (Glimod, Germany) with adjustable sowing rows.

9500 series: A series of potato planters by Double L (Dubuque, IA, USA) offering adjustable sowing rows.

506P: A six-row potato planter by Lockwood (West Fargo, ND, USA) equipped with automatic and hydraulic control systems.

UP3760: A six-row potato planter by Underhaug (Oslo, Norway) featuring a hydraulic motor, and programmable controller for adjusting fertilizer application and seed spacing.

Examples of small-/medium-sized machines include the following:

SPA-2 potato planter: A two-row model by Speedo (Turin, Italy).

P-20M: A two-row potato planter by Small Farm Equipment (Worland, WY, USA).

These advanced foreign models often integrate multiple functionalities, performing tasks like ditching, fertilization, sowing, ridge formation, and suppression. They typically boast sophisticated hydraulic control systems for high levels of automation. However, a key limitation of these machines is the lack of a mulching operation, likely due to their design for specific regional operating climates. Additionally, their large size and high cost make them unsuitable for application in dryland potato production areas like northwest China. Since the 1980s, China has prioritized potato-planting mechanization as a key research area. Extensive research by domestic scholars has led to rapid development and significant progress in Chinese potato-planting machinery [9,10,11,12,13]. Some notable examples include the following:

Film-perforated potato-planting machine: Developed by Sun Wei from Gansu Agricultural University [14].

Triangular chain half-cup spoon-shaped potato-seeding machine: Developed by Duan from Huazhong Agricultural University [15].

1240-type hanging four-row potato-planting machine: Produced by MENOBLE company (Beijing, China).

2CM-4 series potato fertilizer-planting machine: Produced by Heilongjiang Dewo Science and Technology Company Limited (Harbin, China) [16].

2BSL-2 potato ridging seeder: Developed by Inner Mongolia Agricultural University [17].

These Chinese models are well suited for large-scale seeding operations in various northern regions, meeting the agronomic requirements of open-field cultivation.

While some Chinese manufacturers, such as Qingdao Hongzhu Agricultural Machinery (Qingdao, China) (2CM-1/2 model) and Gansu Jiuquan Zhu Long Machinery Manufacturing (Jiuquan, China) (2CMLF-2A model), have introduced film-mulching capabilities, these machines are limited to semi-film ridge cropping. This falls short of the full-film coverage cultivation and planting mode increasingly required for potato production.

Potato film full-coverage ridge furrow cultivation requires adjacent film edge docking, where the ridge furrow is completely covered by the film. Existing mulching planting technology basically adopts film-side soil extraction, requiring the film and the film between bare strips so that mulching institutions can take the soil and make the operating unit walk, which does not meet the full coverage of the film-ridged cultivation agronomic requirements. For this reason, an integrated machine with potato fertilization, seeding, ridging, full-film covering, seeding, and soil covering was designed, and field trials have been conducted to verify its performance.

2. Materials and Methods

2.1. Potato Planting Requirements

Figure 1 shows the ridge shape for potato planting with full-film covering, micro-ditches on the ridge, and soil covering over the seed rows. The planting parameters are as follows: the ridge width is 900 mm, with a height ranging from 150 to 200 mm, and a row spacing of 400 mm. The distance between the micro-ditches among the ridges is 1200 mm. Potatoes are planted on the ridge at a seeding depth of 130 mm. The method utilizes a black plastic film (Shandong Huaxin Plastics industry Co., Ltd., (Liaocheng, China)) measuring 1200 mm in width and 0.01 mm in thickness for full covering, which has drought resistance, water conservation, and good weeding effects. A layer of soil with a width of 170 mm and a thickness ranging from 30 to 50 mm covers the seed rows. To prevent soil crusting over the sprout rows, a mini rainwater collection ditch is set in the middle of the potato ridge to drill seepage holes in the plastic film and cover the micro rainwater ditch to drain excess water.

2.2. General Structure of Integrated Potato-Planting Machine with Full-Film Covering, Micro-Ditch on Ridges, and Soil Covering of Seed Rows

As shown in Figure 2, the integrated machine for potato fertilization, seeding, ridging, and full-film coverage soil covering comprises a frame, fertilizer distribution system, seed distribution system, a gearbox, ditch openers, ground wheels, straddling film-mulching device, ridge-shaping device, and a film-covering mechanism.

2.3. Principles of Operation

The integrated potato machine is connected to a tractor via a three-point suspension device. As the machine moves forward under the tractor’s traction, its ground wheels rotate to drive both the seeding and fertilizer distribution systems through an external chain linked to the wheels. The pointed wing-shaped trencher carves a “V”-shaped trench for seeding while two sets of spoon-chain seed distributors within the seed box cast the potato seeds into the trench, completing the seeding process. Simultaneously, the shaft coupler transmits the tractor’s power output through the gearbox to a sprocket engaging the chain over film soil-covering devices on both sides and a lateral conveyor. The trenching shovel scoops up the soil, lifting the soil over the film-covering mechanism and delivering it towards the lateral conveyor. After the straddling film-mulching device lifts the soil, it forms two ridges on the surface with a large ridge in the middle. The ridge-shaping device further defines these ridges, creating a shallow micro-ditch at their apexes. The film-covering mechanism spreads the film onto the shaped ridge surface while the soil-covering device evenly spreads the soil delivered by the straddling film-mulching device directly above the planting rows on both sides of the film, as shown in Figure 3. In one operation of the unit, a micro-ditch, a large ridge, and two seed rows are formed in the middle. In the next operation, the edges of the adjacent ridges and furrows are connected to each other to ensure full-film covering.

3. Design of Main Working Parts

3.1. Fertilizer Drainage System

By adopting the method of side-deep fertilization, the fertilizer is positioned under the seed potato, which facilitates easy absorption by the seeds without causing burning and ensures high fertilizer efficiency. The full-film covering, micro furrows on ridges, and seed row mulching potato-planting integrated machine uses an external groove wheel fertilizer-dispensing device to discharge fertilizer. Its working principle and structure are similar to those of the external groove wheel seed dispenser. However, different from the outer groove wheel seed-metering device, the diameter of the fertilizer-metering wheel is increased and the number of teeth is reduced, which increases the volume between grooves. During operation, the external groove wheel, driven by a chain, rotates within the ground wheel. The fertilizer fills the groove of the groove wheel by its own gravity and is rotated along with the groove for forced discharge. Additionally, a layer of seeds, located outside the groove wheel, is carried along by the rotation of the outer circumference of the wheel and the friction between the fertilizer particles. Finally, the fertilizer, forced out by the groove wheel and carried by this layer, falls from the fertilizer outlet into the fertilizer pipe and subsequently into the micro trench through the trencher.

According to the working principle of the outer groove wheel, the amount of fertilizer discharged per revolution of the groove wheel can be calculated according to the following formula [18,19].

$$\left\{\begin{array}{l}{q}_1=\rho \tau zsL/1000\\ q_2=2\rho \pi RL\lambda /1000\\ q=q_1+q_2\end{array}\right.$$

(1)

where $q$ is discharged fertilizer mass (g) after the groove wheel rotating one week, $q_1$ is the mass fertilizer (g) forced out by the groove wheel, $q_2$ is the mass of fertilizer (g/r) discharged between the groove wheel outer layer and shell (driven layer), $\tau$ is the coefficient of fullness of the fertilizer in the groove of the groove wheel, z is the number of grooves in the wheel, $\rho$ is the density of fertilizer particles (g/cm³), s is the cross-section of the individual grooves (mm²), L is the effective working length of the groove wheel (mm), R is the radius of the groove wheel (mm), and $\lambda$ is the fullness coefficient of the drive-layer fertilizer (mm).

The fertilizer discharge system of the potato full-film covering, micro-groove on the ridge, and seed row mulching integrated machine consists of two sets of fertilizer boxes, external groove wheel-type fertilizer dischargers, a fertilizer delivery box, a fertilizer discharge pipe, a centrally placed fertilizer discharge box, fertilizer volume adjusting handwheels, a tilted disc-type fertilizer application opener, and other components. Among these components, based on the characteristics of potato planting, the operating width B of the fertilizer boxes within the fertilizer discharge system was selected as 1200 mm. Consequently, the total volume of the left and right fertilizer boxes is determined accordingly [20].

$$V=\frac{1.1LB{Q}_{max}}{10000\gamma }$$

(2)

where V is the total volume of the fertilizer tank in liters; L is the fertilization distance covered by one fertilizer tank fully loaded with fertilizer, set to 1000 m; B is the working width of the fertilizer discharge system, taken as 1200 mm; Q_max is the maximum fertilizer application rate, taken as 370 kg/hm²; and $\gamma$ for the density of diammonium phosphate, taken as 0.80 kg/liter [21].

Calculated from Equation (2), the total volume of fertilizer tank C = 65.12 L.

3.2. Seed Discharge Systems

The spoon chain seed discharger is a type of seed-discharging device commonly utilized in small- and medium-sized potato planters currently. Its performance has a direct impact on the quality and efficiency of the seeding operation [22]. The spoon chain seed discharger was selected which consists of a seed replenishment box, a seed discharging box, a spacer, and an arch-breaking device. The spacer was installed between the seed replenishment box and the seed discharge box while the arch-breaking device was positioned in the lower part of the seed discharge box, as illustrated in Figure 4.

Ideally, the number of seed potatoes dropped into the seed furrow by a single seeding equals the number of seed potatoes discharged from the seed discharger. Subsequently, the equation is established [23].

$$\frac{V\Delta t}{L_2}=\frac{v\Delta t}{l_1}\mathrm{or}\frac{V}{L_2}=\frac{v}{l_1}$$

(3)

where V is the forward speed of the integrated machine, m/s, take 0.50~0.56 m/s; $v$ is the line speed of chain spoon seeder; in order to ensure the quality of seeding, take the maximum value as 0.55 m/s; $L_2$ is the theoretical spacing, based on the agronomic requirements of the two rows of planting in large ridges to take 130 mm; $l_1$ (mm) is the distance between the chain and the spoon; and $\Delta t$ (s) is the time.

Calculated from the above formula, the seed spoon spacing is 128~143 mm, with a middle value of 136 mm. The machine seed discharger adopts a 12A-type chain with a chain pitch of 19.05 mm. So, every seven sections are arranged with double side curved plates to install the seed spoon, as shown in Figure 5. Among the many factors affecting the performance of the spoon chain seeder, the size of the seed spoon and the seed capacity height (the length of the discharging chain buried in the seed layer) are the most critical. The weight of cubed potatoes is about 50 g, and the density of potatoes is between 1000 and 1200 kg/m³. Therefore, the equivalent diameter of cubed potatoes is between 34.2 and 36.2 mm. Considering the large differences in the shape of cubed potatoes, the inner wall of the seed spoon is SR30 mm spherical with a depth of 18 mm. Likewise, in order to improve the performance of seed filling, the height of the seed spoon’s opening is made greater than the height of its sides and the mouth of the spoon adopts a large radius arc.

3.2.1. Trapezoidal Seed Boxes

In field applications, it was found that leaked sowing, especially continuous leakage, often occurs in the early stages of sowing. In the traditional ladder-type seed box structures, factors such as round-trip travel, working width, and the maximum sowing volume per unit area are considered when calculating volume capacity. However, the structural size design of the seed box adopts an empirical design method that fails to consider the structural shape of the seed box and the influence of seed potato shape and body characteristics on potato mechanical distribution and transfer characteristics within the seed box. When seed potatoes are stored in the seed replenishment box, they are supported by the wall of the box and undergo mutual extrusion between seed potato particles that result in the seed potatoes arch at the outlet of the reseeding box. Due to the stable structure, the seed potatoes cannot fall by their own gravity, and the number of seed potatoes in the seed box cannot be guaranteed, thus affecting the accuracy of continuous sowing. Therefore, it is necessary to establish a seed potato contact mechanics model with the seed box as the boundary. At the same time, it is also important to establish the seed potato mechanical equation when the seed potatoes are arched and balanced in the box so as to reveal the arching mechanism. We also optimized and improved the traditional seed box and designed an arch-breaking device to complete continuous and effective sowing operations.

Due to the inherent physical properties of seed potatoes, when the discharge opening of the seed box is reduced to a certain critical value, a bridging phenomenon will occur. As shown in Figure 6, considering the potato group inside the seed box as a whole, the process of critical limit arching at the outlet of the seed box can be simplified into a mechanical geometry model.

In the arched seed potato layer (see Figure 6), assuming that the applied stress on the surfaces AB and CD of the seed box wall is $\sigma$, the stress can be divided into the shear stress ${\tau }_b$ and normal stress ${\sigma }_b$. Let A be the area of the hole and L be the perimeter of the hole. Assuming that the shear stress is approximately constant along the entire perimeter of the hole, when the seed potatoes inside the seed box reach a state of stress equilibrium, a stable arch is formed. The force balance equation [24] for the stable arch is as follows:

$$A\Delta h\rho g=L\Delta h{\tau }_b$$

(4)

where Δh is the height of the discrete cell (m), ρ is the seed potato bulk density (kg/m³), and g is the free-fall acceleration (m/s²).

Assuming that the seed potato is in limiting equilibrium at all points along the perimeter of the hole, by making a Mohr’s stress circle [25], there are:

$${\tau }_b={\tau }_0\left(1+\sin \phi \right)$$

(5)

where ${\tau }_0$ is the seed potato initial shear stress (Pa) and $\phi$ is the seed potato internal friction angle.

Based on the size of the seed scoop, for the rectangular discharge opening of this seed box, the gap between the discharge openings (the width of the rectangular hole) is denoted as b and the length of the hole is l. Combining Equations (4) and (5), the critical condition for the seed box to form an arch with the width of the rectangular seeding rows can be expressed as:

$$b=\frac{2{\tau }_{0}l\left(1+\sin \phi \right)}{l\rho g-2{\tau }_0\left(1+\sin \phi \right)}$$

(6)

According to the phenomenon and causes of arching, in order to prevent arching during seed discharge, it is crucial to disrupt the critical conditions that facilitate the formation of arches by seed potatoes in the design of seed boxes. This can be achieved by increasing the inclination angle of the seed box wall, utilizing asymmetrical shapes for the seed box, positioning the discharge opening along the vertical wall, and incorporating transitional seed boxes. These methods can effectively reduce the likelihood of arching to ensure the smooth discharge of the seed potatoes.

3.2.2. Arch Breakers

To prevent the arching of potato seeds, improve their flowability within the seed box, and avoid delayed replenishment issues from the main seed box to the planting seed box that could lead to missed sowing, the integrated machine adopted a mechanical vibration arch-breaking device based on methods commonly used in industrial material warehouses. The ground wheel drives the sprocket to rotate which generates an impact on the rubber plate installed at the position where potato flowability is poorest and the load is heaviest, which disrupts the stability of the potato cluster through the vibration of the rubber plate. To optimize the arch-breaking effect and determine the ideal installation position of the mechanical vibration device, we created a three-dimensional model of the potatoes using the SolidWorks 2019 software and imported it into the EDEM 2020 discrete element method (DEM) software from Altair [26]. To ensure controlled experimental conditions, we used intact potatoes weighing approximately 80 g in our study. The shape of the potatoes was approximated using a multi-sphere aggregation filling method, as shown in Figure 7a. The material parameters of the seed potatoes and seed boxes as well as the contact parameters between the seed potatoes and seed boxes were obtained from reference [27] as shown in

Table 1. Mechanical properties and contact simulation parameters of seed potato and seed box.

Material Parameter
Materials	Density	Shear Modulus	Poisson Ratio
Potato seed	1048	1.366	0.57
Seed box (steel plate)	7800	70,000	0.30
Contact Parameter
Collision Form	Collision Recovery Coefficient	Static Friction Factor	Dynamic Friction Factor
Plant potatoes and plant potatoes	0.79	0.452	0.242
Plant potato and seed box	0.71	0.445	0.269

. In the EDEM 2020 software, we selected the Hertz–Mindlin (no-slip) contact mechanics model. As depicted in Figure 7b, the simulation process aimed to replicate the flow behavior of the potatoes within the seed box and analyze load distribution during arch formation.

As shown in Figure 7c, the vibration device was installed in the part of the seed box where arching was most prone to occur. This arch-breaking device effectively eliminates or reduces the compressive stress and friction between arched potatoes on the free surface, thereby preventing arch formation. In subsequent field trials, this device demonstrated high effectiveness in mitigating missed sowing issues caused by poor potato flowability.

3.3. Sharp and Wing-Shaped Furrow Opener

The technology of promoting growth by covering soil above the film requires that the soil covering strip aligns up and down precisely with the seed row to prevent the stem sprouts from hitting the exposed mulch which can cause high-temperature damage to the seedlings. For this purpose, a sharp and wing-shaped furrow opener was designed. The dry-farming mulch-covering potato cultivation technique demands high uniformity, and stability in sowing and controlling seeding depth is also a crucial factor. As shown in Figure 8, the opener consists of a front blade, side wings, and a shovel handle. The front blade cuts through the stubble (in the dry-farming areas of the northwest Loess Plateau, potato or corn rotation is commonly used) and the side wings form a “V”-shaped seed trench, ensuring the stability of the potato pieces at the bottom of the trench. The height of the front blade h₂ is set as 130 mm consistent with the seeding depth; the height of the side wing plate h₁ is set as 270 mm, and the rear wing height h₃ is set as 100 mm; the width of the opener b₁ is slightly larger than the width of the seed protection trough set as 85 mm; to ensure the front blade’s slicing action on the soil, α₁ > π/2 + φ₁, where φ₁ is the friction angle between the soil and the blade, φ₁ = 14°~38°, and α₁ is set to 128°; and to allow the soil on the side wing surfaces to slide backward and reduce working resistance, β₁ < π − 2φ₁, and β₁ is set to 104° [28].

In Figure 8, h₁ is the height of the flank plate in mm; h₂ is the height of the front edge in mm; h₃ is the height of the rear wing in mm; α₁ is the rake angle of the front edge; β₁ is the flare angle of the flank plate.

3.4. Ridge-Shaping Device

Covering potato cultivation with plastic mulch not only helps retain moisture and increase temperature but also serves as a weed control measure. This requires the film to be tightly adhered to the ridge surface without any damage. One of the reasons for the damage to the plastic film is the unevenness of the ridge surface and the presence of soil clods on the ridge surface. To ensure a smooth ridge shape and prevent surface soil clods from damaging the integrity of the plastic film, a ridge-shaping device was designed. The structure of the ridge-shaping device is shown in Figure 9. During operation, the soil is pressed down by the pre-tensioning device to form the ridge shape [29].

3.5. Cross-Over Film-Mulching Device

Domestic research on film mulching mechanisms mainly focuses on half-film planting modes, including roller types, drum types, and rotary tillage types [27]. These types of soil-covering mechanisms all adopt the method of taking soil from the side of the film and transporting the covering soil transversely. However, this approach often leaves exposed strips between the mulch films which do not meet the requirements for full-film covering. Therefore, we designed a straddling film-mulching device that collects soil in front of the film. As shown in Figure 10, the film-mulching device consists of an open ditch soil shovel, scraper-lifting belt, lifter tensioning mechanism, lateral conveyor, mulching unit, drive wheel, and driven wheel. The film-mulching device is connected to the planting machine frame via positive and negative buckle adjusters. The installation angle of the overall device was set to ensure that the scraper-lifting belt operates at a 45° angle to the horizontal plane [28,29].

3.5.1. Trenching and Extraction Shovels

The primary function of the trenching sampler shovel is to dig up the soil and transfer it to the scraper. After excavation, a rainwater collection trench is formed on the ground with a rainwater collection surface between the two shovels. According to the agronomic requirements, the spacing between the two shovels is 400 mm. The cover of the shovel is designed in a trapezoidal shape with a width (b) consistent with the conveyor belt and set at 150 mm. To minimize the working resistance of the scraper conveyor belt and avoid the direct scraping of the bottom soil of the rainwater collection trench when the scraper moves vertically below the driven wheel, the front end of the trenching and soil excavation shovel should be lower than the apex of the scraper with a vertical distance (δ) of 20 mm. To prevent interference between the scraper and the rear end of the trenching shovel during operation, a clearance distance (δ′) of 25 mm was set. In order to ensure a smooth flow of soil on the trenching shovel without accumulation, after repeated experiments, the entry angle (α) of the trenching shovel is set at 30° and the length is set at 80 mm.

Within the time interval of the two scrapers taking soil successively, the distance traveled by the unit is s = l/i, then the soil lifting volume q

$$q\approx bHl/i$$

(7)

where b is the width of the lifting belt (mm), H is the excavation depth (mm), l is the spacing of scrapers (mm), and i is the ratio of the speed v′ of the lifting belt to the forward speed v.

The soil lifting volume q should be greater than the soil conveying capacity of the scraper, then

$$H>\left\{\begin{array}{cc}i{h}^2/\left[2\tan \left(\gamma -\psi \right)l\right]& forl\ge h/\tan \left(\gamma -\psi \right)\\ i/\left[h-l\tan \left(\gamma -\psi \right)/2\right]& forl<h/\tan \left(\gamma -\psi \right)\end{array}\right.$$

(8)

where γ is the angle between the scraper lifting belt and the horizontal plane (°), ψ is the angle of internal friction of the soil (°), and h is the height of the scraper (mm).

From this, it can be seen that the depth of the soil-lifting shovel in the soil affects the amount of soil lifted. In operation, due to differences in soil types and cultivation methods, the same structural parameters of the unit at different depths of subsidence lead to inconsistent soil depths. Therefore, to adapt to different working conditions, as shown in Figure 10, the positive and negative buckle regulator was designed to adjust the depth. If the soil is soft and the unit sinks more, it can rotate the silk sleeve so that the positive and negative silk rod, which are at the end of the silk sleeve, can be screwed in and the positive and negative buckle depth adjuster becomes shorter, and the soil lifting shovel digging depth becomes shallower, and vice versa.

3.5.2. Scraper Lift Belt

Figure 11 shows the movement analysis of the scraper. The soil surface on the scraper and the horizontal plane form an angle ψ which is the internal friction angle of the soil. The amount of soil on each scraper is the transport volume of the belt with a length l and the volume is obtained by multiplying the transverse area and the width of the scraper. Then, the amount of soil Q covered by the film of a certain length l′ is [20]

$$Q=\left\{\begin{array}{cc}\eta ib{l}^{\prime }{h}^2/\left[2\tan \left(\gamma -\psi \right)l\right]& forl\ge h/\tan \left(\gamma -\psi \right)\\ \eta b{l}^{\prime }i\left[h-l\tan \left(\gamma -\psi \right)/2\right]& forl<h/\tan \left(\gamma -\psi \right)\end{array}\right.$$

(9)

where η is the conveying efficiency which is mainly related to the filling factor and the slipping rate of the lifting belt.

In Figure 11, ω is the angular velocity of the driven wheel in rad/s; v is the forward velocity in m/s; H is the depth of plowing in mm; γ is the angle between the lifting belt and the horizontal plane; ψ is the soil internal frictional angle; r is the radius of the driven wheel in mm; h is the height of the scraper in mm; l is the scraper spacing in mm; v′ is the velocity of the lifting belt in m/s; δ is the clearance between the scraper and bottom in mm; α is the penetration angle of the trenching shovel.

According to the requirements of soil covering for row mulching cultivation, the width of soil to be covered on the mulch film is 170 mm with a thickness of 30–50 mm. The soil covering on a single side of the film edge is 100 mm wide with a thickness of between 30 and 50 mm. Therefore, the soil volume covered by the film per unit length is between 8.1 × 10⁻³ and 1.4 × 10⁻² m³. The equipment utilizes a 5 × 150 mm rubber canvas transmission belt with a scraper spacing l = 100 mm and a scraper height h = 60 mm. The ratio of the conveyor belt speed (v′) to the forward speed (v) is 1.35. According to Equation (3), the theoretical soil conveying capacity of the conveyor belt is calculated to be 0.016 m³ which meets the design requirements.

To adjust the tension of the belt, as shown in Figure 10, a tensioning mechanism was designed. By adjusting the length of the tie rods on both sides, the driven wheel axle moves forward and backward to achieve tightness adjustment. To prevent soil from adhering to the follower wheel and affecting its function, the assembly relationship is disrupted by changing the radius of the follower wheel. Additionally, a soil-clearing device is installed within the tensioning mechanism. The clearing device mainly consists of two rubber scrapers. One scraper is positioned against the driven wheel to clean off any soil adhered to it, while the other scraper is positioned against the back of the lifting belt to clear any soil that enters the back of the belt.

3.5.3. Counter-Row Mulching Devices

After the soil excavation process, ridge furrows are formed on the ground with a spacing of 1200 mm between them. This means that the distance between the centers of the two sets of soil-covering devices on the film is 1200 mm. The row spacing (refers to the distance between two trenchers) is set at 400 mm. In order to ensure that the soil is properly covered directly above the rows, the soil lifted by the conveyor belt needs to be laterally transported to a certain distance. To achieve this, a helical conveyor is used for lateral soil transportation as illustrated in Figure 12. The width of the scraper conveyor belt is b = 150 mm while the desired soil coverage width is 170 mm. To enhance the debris removal capability of the conveyor and prevent blockages caused by crop residues and stones, the helical conveyor was designed with an outer diameter D = 150 mm, a shaft diameter d = 48 mm, an auger pitch p = 150 mm, and a clearance λ = 5 mm between the blades and the bottom shell. Moreover, to improve the structural strength of the conveyor and protect the blades from damage, unequal thickness blades are employed with a thickness s₁ = 2.5 mm and a total thickness s = 5 mm [20].

In Figure 12, S is the blade thickness in mm; D is the outer diameter of the screw conveyor in mm; d is the shaft diameter of the screw conveyor in mm; p is the pitch of the screw conveyor in mm.

The screw conveyor transport volume Q′ is as follows [30]:

$$Q^{\prime }=\frac{\mathsf{\pi }}{24}\left[(D-2\lambda {)}^2-d^2\right]{\eta }^{\prime }pnC\times 10^{10}$$

(10)

where λ is the gap between the blade and the bottom shell (mm); η′ is the filling coefficient, taken as 0.3; auger pitch p = 150 mm; n is the rotational speed (rpm); and C is the conveyor inclined conveying coefficient (taken as 1) due to the horizontal arrangement of the screw conveyor.

At an operating speed of 1 m/s for the unit, the volume of soil transported by the screw conveyor should match the volume transported by the elevated belt calculated using Formula (4). The rotational speed of the screw conveyor is set at 140 rpm, and the resulting volume of soil pushed and transported by the screw conveyor is 0.016 m³ which meets the design requirements.

4. Results

4.1. Experiment Conditions

The field trial of the soil-covering device was conducted in Chaijiatai, Xiliugou Street, Xigu District, Lanzhou City, located in the arid farming area of the Loess Plateau in central Gansu Province. The experimental soil consisted of yellow loam with a moisture content of 17.83%, a bulk density ranging from 1.31 to 1.37 g/cm³, and a firmness below 254 × 10³ Pa. The field terrain was relatively flat with loose soil and minimal weed presence. The experimental site spanned a length of 100 m. The seed potatoes used in the experiment had average dimensions of 67.4 mm × 51.4 mm × 38.6 mm, a moisture content of 69.7%, and an average mass of 78.9 g per potato. The soil-covering device was paired with a Dongfanghong-300 tractor which provided a power output of 22.1 kW and was suitable for the experimental setup [31].

4.2. Experiment Program and Methodology

After the completion of the operation, the performance of the potato planter was evaluated according to the requirements specified in GB/T 25417-2010 “Technical Conditions for Potato-Planting Machines” and NY/T 1415-2007 “Technical Specifications for Quality Evaluation of Potato-Planting Machines” and NY/T 987-2006 “Quality Requirements for Film-Mulching and Hole-Seeding Machines [32,33,34]”. The experiment value of the qualification rate of planting depth, coverage width between rows, coverage thickness between rows, adjacent row spacing, mechanical damage to the light-transmitting surface of the film, and the spacing qualification rate of water seepage holes was measured [35,36].

The method used for determining the qualification rate of planting depth involved dividing the field into four quadrants by drawing a cross-line along the length and width of the plot. Two randomly selected diagonally opposite quadrants were chosen as the testing samples. Within each sample quadrant, five sub-plots were selected along the diagonal line with each sub-plot measuring 4.5 m in length (approximately 12 hole distances). Three rows were measured in each sub-plot with a total of 20 points measured using the holes as reference points. The soil bed was vertically cut open to measure the sowing depth and spacing between the seed potatoes on the profile.

$$\epsilon =\frac{k_1}{k_0}\times 100\%$$

(11)

$$\tau =\frac{k_2}{k_0}\times 100\%$$

(12)

where ε is the planting depth qualification rate (%); τ is the seed potato spacing qualification index (%); k₀ is the total number of measurements, one; k₁ is the number of qualified planting depth, one; and k₂ is the number of qualified seed potato spacing, one.

Method for Determining the Degree of Mechanical Damage to the Light-Transmitting Surface of the Film: Randomly select a 5-meter-long section of the film for measurement. Within this section, precisely measure both the length and width of the mechanical damage on the light-transmitting surface and the width of any flattened areas of the light-transmitting surface. Repeat this process for a total of 10 test areas, and calculate the average value to obtain the final test result.

$$\eta \prime =\frac{\Sigma L_i}{L\prime b\prime }$$

(13)

where η′ is the degree of the mechanical breakage of the light surface of the film (mm/m²); L_i is the seam length or edge length of the light surface mechanically broken at the I place in the experiment area (mm); L′ is the length of the experiment area, m; and b′ is the average value of the spreading width of the light surface in the experiment area, m.

Method for Determining the Qualification Rate of Coverage Width and Coverage Thickness between Rows: Randomly select measurement points and measure the coverage width and coverage thickness between the rows at each measurement point. Calculate the average values.

$$\zeta =\frac{m_1}{m_0}\times 100\%$$

(14)

$$f=\frac{m_2}{m_0}\times 100\%$$

(15)

where ζ is the qualification rate of seed row mulch width (%), f is the qualification rate of seed row mulch thickness (%), m₀ is the total number of measurement points, m₁ is the number of qualification points of seed row mulch width, and m₂ is the number of qualification points of seed row mulch thickness.

Method for Determining the Qualification Rate of Adjacent Row Spacing: After emergence, researchers should set up plots perpendicular to the adjacent rows, with each plot measuring 5 m in length. Within each plot, mark 10 measurement points evenly spaced along the adjacent rows and measure the adjacent row spacing at each point.

$$\sigma =\frac{n_1}{n_0}\times 100\%$$

(16)

where σ is the neighboring row spacing qualification rate (%), n₀ is the total number of neighboring row spacing determination points, and n₁ is the number of neighboring row spacing qualified points.

The results are shown in

Table 2. Results of field experiments.

Index	Potato Planter Prototype	2CM-2 Potato Planter	Technical Requirement
Qualified rate of sowing depth (%)	85.0	84.0	≥80.0
Qualified index of seed tuber spacing (%)	90.0	87.0	≥85.0
Reseeding index (%)	6.0	7.0	≤20.0
Miss-seeding index (%)	3.0	4.2	≤10.0
Qualified rate of soil width covered on planting line (%)	94.0	—	≥90.0
Qualified rate of soil depth covered on planting line (%)	93.0	—	≥90.0
Qualified rate of adjacent row spacing (%)	88.0	—	≥80.0
Damage degree of plastic film (daylight passing/surface area, mm/m2)	30.2	51.3	≤55.0

. Field trials have shown that the qualified rate of sowing depth under the film with the integrated machine for the fertilizing, ridging, and full-film covering of seed rows and soil covering is 85%. The qualified index of seed potato spacing is 90%, the repetitive seeding index is 6%, and the missed seeding index is 3%. The qualified rate for seed row covering soil width is 94%, the qualified rate for seed row covering soil thickness is 93%, the qualified rate of adjacent row spacing is 88%, and the degree of mechanical damage to the light-transmitting surface of the mulch film is 30.2 mm/m². According to Table 2, the designed integrated machine for the fertilization, sowing, ridging, and full-film mulching of potatoes meets the requirements of high-yield cultivation technology with full-film covering. The field performance experiment indicators meet the national and industry standards, and the seed placement performance index was higher than that of the 2CM-2 potato planter. Figure 13 shows the field experiment and effect of the integrated machine for the fertilization, sowing, ridging, and full-film mulching of potato seedlings.

The thickness of the plastic film in this experiment was 0.008 mm; the thickness of covering soil was 55 mm; the spacing of the seepage hole was 300 mm; and the potato variety was favorite.

5. Conclusions

Drawing upon the agronomic requirements of potato planting in full-film double-ridge furrows and considering the growth-promoting mechanism of soil sitting on the film top, an integrated machine for potato fertilization, sowing, ridging, full-film covering, and soil covering was designed.

• The main components of the prototype machine were thoroughly analyzed and designed. Specifically, the structure and working parameters of the seed discharge system, the sharp and wing-shaped furrow opener, and the straddling film-mulching device were meticulously determined. Additionally, the working mechanism of the core components was carefully analyzed. The designed straddle-type film-mulching device effectively meets the agronomic requirements of full-film seed row mulching. Furthermore, the seed discharge system consists of a seed replenishment box, a seed discharge box, and an arch-breaking device. This system has the ability to adjust the seed capacity of the seed discharge box, thereby enhancing the overall performance of the seed discharge system.
• The field trials have shown that the qualified rate of sowing depth under the film with the integrated machine for fertilizing, ridging, and full-film covering of seed rows and soil covering is 85%. The qualified index of seed potato spacing is 90%, the repetitive seeding index is 6%, and the missed seeding index is 3%. The qualified rate for seed row covering soil width is 94%, the qualified rate for seed row covering soil thickness is 93%, the qualified rate of adjacent row spacing is 88%, and the degree of mechanical damage to the light-transmitting surface of the mulch film is 30.2 mm/m². All of the field performance experiment indexes meet the requirements of the national and industry standards.