Design and Simulation of a Combined Trencher for Transverse Sugarcane Planter

Abstract

The trencher design of the pre-cut transverse sugarcane planter is the basis for realizing deep planting and shallow burial. Aimed at the problems of insufficient seeding space provided by furrows and high resistance to trenching, a structural configuration of a combined trencher suitable for transverse cane planting agronomy was proposed to improve the stability, simplicity, and efficiency of trenching. The collaborative operations of components such as the soil lifting of the leak-proof plow, the soil fragmentation and throwing of the double-disc rotary tiller, the rebound of the fender, the lateral diversion of the furrowing plow, and the motion control of the double rocker arms were comprehensively utilized. The trenching principle of using double-sided guards to block soil backfilling to form a seeding space was applied, as well as pre-side diversion to reduce the forward resistance of plow surfaces. The simulation of the trenching process showed that the combined trencher was available in terms of soil particle transfer and dynamic space-forming capabilities, and the stress distribution of the advancing plow surface was analyzed. Moreover, based on the minimum resistance characteristics, the optimal spacing between the rotary tiller and the furrowing plow and the blade arrangement mode were configured, and the structural parameters of the furrowing plow were optimized to include a soil penetration angle of 20°, an oblique cutting angle of 75°, and a curvature radius of 280 mm. Field experiments have proven that the soil entry movement trajectory, the length and width of the accessible seed placement space, and the average planting depth of cane seeds could all achieve respective design anticipations of the combined trencher. The measured trenching resistance was 7609.7 N, with an error of 22.2% from the predicted value under the same configuration.

1. Introduction

In China, Guangxi currently accounts for over 60% of the planting area and sugar production, becoming China’s largest sugarcane cultivation area. However, due to the widespread hilly terrain and scattered small cultivation plots, it is challenging to promote mechanized planting, resulting in high sugar production costs that involve a lot of labor. Therefore, unlike the large multi-row sugarcane planters used in Australia, Brazil, and other countries, the double-row planters developed for hills tend to be small, lightweight, efficient, and integrated. In addition, the research has confirmed that compared with the vertical seed placement pattern, horizontal cane seed placement in rows with furrows can result in a higher emergence rate, less seed consumption, and higher sugar content and yield [1]. Moreover, by cutting the entire sugarcane stem into several double-bud segments and then going through prefabricated processes such as screening and disinfection, the field planting of such pre-cut seeds can effectively improve the nutrient supply quality and seedling emergence rate [2]. Meanwhile, the horizontal planting pattern of double-bud segments can improve the lodging resistance of high straw crops [3]. In summary, the key to developing corresponding pre-cut transverse planters is to use an automatic seed metering device in conjunction with a high-performance trencher to achieve a series of sugarcane planting processes such as stable trenching, continuous and uniform sowing, fertilizing, soil covering, and ridging [4]. In this regard, Taghinezhad et al. [5] analyzed the effects of rake tooth length and seeding speed of the seeding roller on the seed arrangement density. Li et al. [6] and Ma et al. [7] used a microcontroller to control the seed cutting or conveying rate to match the seeding speed to improve the precise and uniform effect of seeding.

However, regarding the requirement that the sugarcane must be planted horizontally in a furrow with a depth of 23~28 cm, the trencher significantly affects the planting depth and width available for placement at the bottom seed bed [8]. It has been proven that the root system of sugarcane seeds in deep trenches and loose soil grows more developed, which is beneficial to improving the lodging resistance and yield [9]. As the core operation assembly, the trencher forms an effective space for seeds to fall into by squeezing or shoveling the soil, so that the seeds and fertilizer can be guided evenly into the seed furrow by the seed guide tube and the fertilizer guide tube, respectively. Therefore, when facing the agronomic requirements of wide furrows, deep planting, and broken soil, it is difficult for traditional rotary tillers or tillage plows (divided into hoe type, wide wing shovel type, core-share type, disc type, etc.) to perform these combined functions by relying on a single soil-engaging component. It is also necessary to consider the trenching resistance that increases exponentially with depth and tillage width.

Regarding the research on components for the purpose of trenching, McLaughlin et al. [10] conducted field experiments on shovel and disc type trenchers at different forward speeds and tillage depths, and obtained the influence of operating conditions. In terms of structural design, Liu et al. [11], Bao et al. [12], and Hou et al. [13] studied the correlation between the inclination angle, soil separation angle, and diversion angle of the wide-winged shovel and core-share plow with the soil disturbance and seed ditch construction, and then obtained the optimal configuration of the trencher to improve the stability of furrow width and ridge height. Dai et al. [14] designed the trencher wings and diverter plates based on the stability of potato seeds attached to the seedbed. For the backflow analysis of trenched soil, He et al. [15] observed the tool movement of a disc trencher and the movement of soil block elements through high-speed images. On the other hand, in terms of trenching resistance, Liu et al. [16] and Tamás et al. [17] measured the trencher power consumption through the theoretical soil cutting–throwing model and soil discrete element model, respectively. Ibrahmi et al. [18] reverse optimized the surface design parameters of a core-share plow with the lowest power consumption as the goal.

In the design of a trencher that combines multiple soil-engaging components, their interacting configuration parameters play a key role in the furrow profile quality of the planter. Barr et al. [19] measured the distribution of seeds, fertilizers, and disturbed soil in a virtual simulation test using the discrete element method (DEM), and conducted a comprehensive optimization based on the interaction between these and the trencher. Liu et al. [20] designed a boat-shaped trencher with a combination of front and rear plows to achieve a trapezoidal trench depth of 19~23 cm and maintain stability above 90%. In addition, Qin et al. [21] explored the relative position and margin of the double-disc trencher, fertilizer applicator, and seed discharge opening. In summary, the formation of the seed furrow space is closely related to the movement relationship between soil and seeds, which depends on the structure and working parameters of the combined trencher.

Faced with the agronomic requirements for trenching in horizontal sugarcane planting, as well as the challenges of insufficient seed placement space and larger trenching resistance, this paper designs a structural configuration of a combined trencher for improved trench profile and resistance characteristics. Based on the specification for transverse double-bud seeding, the trenching principle and drag reduction method for forming a dynamic seeding space under the collaborative operation of multiple components were determined. Through discrete element simulation using measured soil parameters, the trenching process of the interaction between the main components of the combined trencher and soil particles was analyzed. The effects of the crucial configuration parameters of the rotary tiller and furrowing plow on the predicted trenching resistance were obtained based on virtual tests, and these parameters were subsequently optimized. Finally, field experiments were conducted to test the actual movement trajectory of the combined trencher into the soil, the length and width of the seed placement space, the average planting depth of sugarcane seeds, and the trenching resistance. A comprehensive evaluation and verification was carried out to determine whether various performances meet the requirements of transverse cane planting.

2. Materials and Methods

2.1. Agronomic Requirements and Challenges for Transverse Sowing of Cane Seeds

The histogram of the length of over 200 sugarcane seeds prepared using double-bud segments as the cutting standard is shown in Figure 1. It was found that the length of stem segments was mainly concentrated in the range of 26~32 cm, with the maximum length being 36 cm. Therefore, the width of the furrow for transverse seeding should be more than 40 cm to maintain a certain margin. The schematic diagram of the furrow profile is shown in Figure 2a, in which the effective planting depth is defined as the distance from the sugarcane seed to the horizontal ground. According to the agronomic principle of deep planting and shallow burial, the effective planting depth is required to reach 23~28 cm. Since there is still a floating soil layer of 2~3 cm thick at the bottom of cane seeds, the trenching depth needs to be 25~30 cm. For soil accumulated on both sides, the fragmentation rate (the proportion of particles with size below 2.5 cm according to the Guangxi Province Regional Standard [22]) is required to reach more than 70%. As shown in Figure 2b, the row spacing (R_s) required for double-row planters is 1.4 m, and the seed spacing is 30~40 cm. This planting model has better field ventilation, which is beneficial to improving the germination rate of sugarcane and extending the life of ratoons [23], as well as facilitating subsequent cultivating and mechanized harvesting.

In terms of achieving the above performance, the combined trenchers of planters in current production practice are usually prone to the following challenges:

• If the formed furrow bottom is not a rectangular plane but a V-shaped cross-section, cane seeds would collide with the soil when they fall into the furrow. The orientation of cane seeds may change and become suspended in the furrow, causing a small effective planting depth, as shown in Figure 3a.
• Due to the insufficient height of furrowing plow, a large amount of floating soil flows back, resulting in a large difference between the furrow depth and the effective planting depth. Moreover, there is a large amount of agglomerated soil in the middle of the double rotary tillage gearbox due to missed tillage, as shown in Figure 3b.
• When dealing with compacted clay, the trenching resistance and machine power consumption are too high. This in turn causes the problem of breakage of the support base such as plow handles or rotary blade handles, affecting the continuous reliability of the planter’s operation and the quality consistency of furrows.

2.2. Working Principle of Combined Trencher

2.2.1. Overall Structural Configuration

In response to the above problems, according to the functional modular design methodology, the structural configuration of the combined trencher of the double-row transverse sugarcane planter is composed of the following four parts as a whole, as shown in Figure 4a:

(1)

The front leak-proof plow breaks and lifts the leaked soil between the two chain gearboxes, and then guides the soil to both sides.

(2)

The double-disc rotary tiller and fender utilize rotary milling to cut deeper, rapidly breaking up the soil and throwing it up from the furrow, and then rebounding to the side ridges after collision with the fender. The front rotary tillage link improves the quality of soil tillage and helps reduce the forward resistance of subsequent trenching.

(3)

The rear furrowing plow lifts the broken soil materials along the plow surface and directs them to the side, and then uses the side guards to prevent soil from backflowing. The furrow cleared in this way cooperates with the built-in seeding opening to form a dynamic seeding space.

(4)

The cantilever-type movable frame that can be adjusted by dual hydraulic cylinders on the one hand transmits rotary tillage power internally, and on the other hand controls the relative position and cutting angle of the furrowing plow to the ground. The corresponding trencher assembly of the planter manufactured is shown in Figure 4b.

Figure 4. The structural configuration of the combined trencher. (a) Design drawing; (b) manufacturing entity.

Figure 4. The structural configuration of the combined trencher. (a) Design drawing; (b) manufacturing entity.

2.2.2. Principle of Seeding Space Formation through Trenching

The working principle of seeding double-bud stems is introduced as follows. First, the tractor outputs power to the rotary tiller for cutting the soil, and during the advancement, the hydraulic cylinders of the upper and lower arms extend so that the trencher engages into the soil at a predetermined cutting depth to form a seed furrow. In addition, power is input to the seeder and fertilizing mechanism through ground wheels, and the transverse cane seeds are discharged from the seeding opening according to a specific interval. In this process, the formation of a dynamic and effective seeding space is related to the rotary soil throwing, the rebound of the fender, the furrowing plow to clear furrows, the guards to block the soil backfill, and the operating parameters. Therefore, the key to determining spatial stability is the relative position between the seed opening and the trencher. Although the plow surface with a trenching depth of 30 cm and a width greater than the length of the sugarcane section can form a seeding space at once, due to the inherent characteristic of soil backflow on the side slopes of ridges, double-sided guards are needed to block soil backfilling in the seed furrow. Thus, its design length should exceed the seeding point, and its height should block soil from overturning to ensure that the seeding point is before the soil return point, so that the seeding space can effectively last for a period without the interference of backflow.

In terms of drag reduction, the combined trencher mainly reduces the overall trenching resistance in two ways. First, in the initial operation stage, the double rocker arms control the trencher to form a certain cutting-edge angle and gradually make its movement trajectory cut into tillage layers. As a result, the soil penetration resistance for the long-range device to reach a predetermined depth is reduced. Second, in the stable trenching stage, the topsoil is first pulverized by a rotary tiller at the front end, and the portion of the thrown soil is directed to the side by the fender for ridging. Therefore, the reduction in particle size and quantity reduces the forward resistance of the larger plow surface to push the soil.

2.3. Structural Design and Motion Control of Key Components

2.3.1. Design Parameters of the Leak-Proof Plow

The design of the leak-proof plow is aimed at the middle leakage area, which is mainly the surface generated by the guide curve. The guide curve with a total height of 380 mm is divided into a straight segment and a curved segment (with a radius of curvature of 295 mm) from top to bottom. In these circumstances, the opening was designed to be 115 mm to avoid excessive protrusion of the plow tip. In order to distribute the resistance evenly, the width gradually decreased from 150 to 60 mm from top to bottom. In addition, the smaller cross-section and the resistance of leak-proof plow allows for rapid soil entry. Referring to the V-shaped subsoiling component [24], the soil penetration angle was determined as 35°. Since the operation on cultivated land focuses on the diversion performance, the bottom and top opening angles are set to be larger at 65° and 80°, respectively, to facilitate the diversion of soil to the rotary tillage area. And a triangular reinforcement rib was added between the plow surface and the plow handle to establish a leak-proof plow structure, as shown in Figure 5.

2.3.2. Design Parameters of Core-Share Furrowing Plow

The furrowing surface of the core-share plow was mainly generated by a guide curve, which consisted of three segments, including a 140 mm long edge line for quickly cutting into the topsoil, an arc curve with a curvature radius of R_c (within the range of 245~280 mm), and a 250 mm long vertical line without overturning. In addition, as per practical experience, the height of the furrowing plow was generally 1.2 times the sum of the maximum trenching depth of 30 cm and the ridge height of 15 cm, equaling to 54 cm. Since the length of cane seeds is concentrated between 26 and 32 cm and less than 36 cm, the plow width (B) was greater than 1.4 times the average seed length, equaling to 40 cm. These described structural parameters are shown in Figure 6. Supplementally, since the length and width of furrowing plow used for horizontal sugarcane planting are both considerable, in order to balance the soil-engaging stroke and resistance, the soil penetration angle (α) and the oblique cutting angle (β) were selected within the ranges of 20~30° and 65~75°, respectively. Since the specific values of these two parameters along with R_c significantly affect the trenching performance, they were determined through subsequent simulation tests as design variables.

On the other hand, the design of the double-sided guards of the furrowing plow is critical, playing an important role in instantly blocking soil from backfilling the seed furrow and preventing damage to the seeding space. The length of the guard was determined to be 70 cm including the subsequent seeding point, and its height was the same as the plow height. As for the lateral deflection angle ξ of the guard, the upper width between the two guards should be larger than the lower width, that is, ξ was taken as 5° to prevent soil particles from sliding down the slopes on both sides of the furrow.

2.3.3. Parameter Design of Rotary Tillage with Fender

The focus in designing rotary tillage in a combined trencher is the soil crushing quality and the ability to transfer particles laterally. For this purpose, the single-sided configuration adopts a rotary tiller with double cutterheads and an upper fender. The effective tillage width of a single rotary tiller is 12.5 cm, which is divided into two cutting sub-areas. The total tillage width on both sides is 40 cm, which can cover over the width of subsequent trenching. A single cutterhead is equipped with a total of six left and right rake blades, each of which is welded by a 23 mm long handle and a curved blade with a certain angle.

The arrangement of these rake blades is an important factor affecting rotary tillage resistance, soil fragmentation, and throwing performance, taking into account the following requirements: (1) the left and right rake blades are inserted into the soil alternately to balance the lateral reaction force of cutting soil, reducing the deflection moment of the assembly in the horizontal plane and the axial impact load on the blade shaft bearing; (2) the soil cutting pitch of each tool in the sub-area should be similar to reduce the torque fluctuation of cutting resistance and ensure balanced fragmentation and wear; (3) the circumferential angle between the two adjacent rake blades with the same axial cross-section should be as large as possible to avoid clogging with soil and affecting throwing. Thereby, the three arrangements shown in Figure 7 were designed based on the staggered nature between two cutterheads: Mode-1 was set to a stagger angle of 0°, and the rake blade had a consistent deflection direction; Mode-2 was set to a staggered angle between cutterheads that was half the circumferential angle of the blade, so that the left or right rake blade formed three spirals; and Mode-3 was set to a staggered angle equal to a circumferential angle, so that the left and right rake blades were oppositely symmetrical.

Generally, the ratio of the rotary tangential speed of rotating blade tip to the forward speed (v_m) was defined as the rotary tillage speed ratio (λ), and its size corresponds to the different cycloidal motion forms of cutting tips, as follows:

$$\lambda ={\displaystyle \frac{\omega r}{v_m}}$$

(1)

where r is the rotary radius of the blade, equal to 29 cm and ω is the rotary angular velocity. Further, the cutting pitch (P, mm) is defined as follows:

$$P={\displaystyle \frac{6000v_m}{nz}}={\displaystyle \frac{\pi r}{5\lambda z}}$$

(2)

where n was the rotational speed of the blade axis and z was the number of blade installations per unit of cutting sub-area, which was equal to 3. The size of P directly affects the quality of soil crushing and the flatness of the furrow bottom. The larger the selected λ, the smaller the p value, implying a better crushing quality with less resistance. However, too low a forward speed can lead to low operating efficiency, so the values of these two parameters need to be reasonably matched. When trenching for planting sugarcane, the planter responds to a trench depth of 30 cm superimposed on a width of 40 cm. In this case, the amount of soil processed per unit time is large, so it is appropriate to select a slower gear Ⅰ (about 0.65 m/s) to match a larger rotating speed of above 200 r/min. The maximum soil cutting pitch was calculated to be 180 mm.

In addition, the function of the fender is to use a fixed slope to rebound soil particles thrown up by rotary tillage to the side accumulation, in order to assist in clearing the furrow and to prevent soil from spreading into the transmission box, fertilizer, seeder, and other parts. For this reason, the fender designed is shown in Figure 8a, which adopts a positive 45° skewed arc to intersect with a straight arc plate and a negative 45° skewed arc. Thus, the particles could be gathered and thrown to the side through the constraint effect of enveloping curved walls, as shown in Figure 8b.

2.3.4. Motion Control of Double Rocker Arms

Since the total length of the combined trencher is relatively large, it is important to control its attitude angle and movement trajectory in the initial stage of trenching to gradually cut into tillage layers. Thus, the goal is to achieve a smaller soil-engaging stroke and trenching resistance in the process of reaching the predetermined furrow depth. As shown in Figure 9, the trencher is suspended from the frame of the planter using double rocker arms. It can adjust the real-time soil penetration angle and the soil-engaging pressure supplied by the upper arm’s hydraulic cylinder independently of the tractor’s three-point suspension, thereby realizing feedback control of the cutting depth.

The control logic is as follows. In the initial state, the angle between the upper and lower arms is 90°, so that the trencher assumes a horizontal attitude. When starting cutting, a larger initial cutting angle (γ, generally taken as 15~18°) is selected to quickly cut into the ground. Subsequently, the hydraulic cylinder of the lower arm is extended to increase the soil penetration angle, and as the upper arm is extended, the cutting depth continues to increase linearly. When approaching the predetermined depth, the lower arm reduces the soil penetration angle to approach a smaller soil gap angle (γ₀, generally taken as 5~8°). After reaching the specified depth, the trencher returns to the horizontal attitude and fixes the hydraulic cylinders of upper and lower arms. The above is represented by the attenuation trajectory curve in Figure 9. Designing such a movement manner is conductive to obtaining the comprehensive minimum progressive trenching resistance [25].

The soil-engaging stroke (S) can be calculated as follows:

$$S={\displaystyle \frac{a}{\mathit{tan}\gamma }}$$

(3)

The smaller the value, the better the energy consumption performance of progressive cutting into the soil. It can be inferred that as γ increases, the stroke will become smaller, but the soil-engaging resistance will increase accordingly. A larger trenching depth can also lead to a larger S.

2.4. Simulation of Trenching Process

2.4.1. Establishment of EDEM Model

For soil samples taken from the sugarcane planting area in Fusui County, Chongzuo City, Guangxi Province, the average moisture content during the spring operation season was measured to be 8%. The soil property parameters such as recovery coefficient, static friction coefficient, and rolling friction coefficient between the soil particles and soil-65 Mn steel were measured by slope collision tests, friction-sliding tests, and angle of repose tests (as shown in Figure 10). Due to the apparent bonding phenomenon for the collected latosol clay, the contact model between particles adopted the Hertz–Mindlin with JKR model that mainly considered bonding force [26]. After a series of virtual calibrations, the mechanical parameters required for soil discrete element modeling were obtained, as shown in

Table 1. Soil mechanical parameters assigned in the DEM model.

Property Type	Parameters	Values
Soil particles	Density (kg·m−3)	1786
	Poisson’s ratio	0.46
	Shear modulus (MPa)	1.0
	Recovery coefficient	0.63
	Static friction coefficient	0.91
	Dynamic friction coefficient	0.07
	JKR surface energy (J·m−2)	5.59
Soil particle-65 Mn steel	Recovery coefficient	0.56
	Static friction coefficient	0.71
	Dynamic friction coefficient	0.10

.

Using the above parameters, a soil bin model with 1500 mm × 1000 mm × 400 mm was constructed in the EDEM software (2020 version), and the geometric model of the combined trencher was imported. The simulation model obtained is shown in Figure 11a, in which different tillage layers are divided at a height of 10 cm and displayed differentially by color to analyze the disturbed flow of particles. The Rayleigh step time was set to 20%, and the simulation duration was 3 s. The constant operating parameters used in the simulation are a rotary tillage speed of 200 r/min, forward speed of 0.65 m/s, and cutting depth of 300 mm.

2.4.2. Setup for Virtual Tests

The longitudinal relative distance between the rotary tiller and the furrowing plow is a crucial design parameter that affects soil congestion and collaboration performance, as shown in Figure 11b. Therefore, it was set as a virtual test variable (L, with a feasible interval of 45~89 cm) to find a better arrangement solution through single-factor virtual tests at five levels (taken as 45, 56, 67, 78, and 89 cm). The corresponding evaluation indicators were the cutting force of a single rotary blade and the trenching resistance extracted from the simulation results. In addition, for the design optimization of important structural variables of furrowing plow mentioned above, a three-factor, three-level orthogonal test was conducted as shown in

Table 2. Structural variables and level settings for the furrowing plow.

Test Factors	Level-1	Level-2	Level-3
Soil penetration angle, α (°)	20	25	30
Oblique cutting angle, β (°)	65	70	75
Curvature radius, Rc (mm)	245	262.5	280

, and the resistance to trenching was used as the response index.

2.5. Field Experiments

As shown in Figure 12a, about five acres of deeply loosened and leveled planting fields were selected in Fusui County, Chongzuo City, Guangxi Province. The average moisture content of the cultivated land was measured to be 8%. Double-bud segment cane seeds of Zhongzhe No. 9 variety were used in the field experiments. The manufactured combined trencher was used for joint operations of dual-row rotary tillage, trenching, fertilizing, and seeding. The working state of trenching at a cutting depth of 30 cm is maintained as shown in Figure 12b. By regulating the output throttle of the tractor and calibrated by a laser speedometer, the rotary speed and forward speed were brought up to predetermined 200 r/min and 0.65 m/s, respectively.

The evaluation of the field performance of the trencher mainly focused on two aspects, the planting depth and trenching resistance. The method of measuring the depth of the furrow profile is shown in Figure 12c, in which the height difference between the transversely buried cane seeds and the ground surface was defined as the planting depth (D_p). By pasting strain gauges (S₁~S₄) along different directions on different planes of the furrowing plow handle, the trenching forward resistance, bidirectional lateral force, and vertical positive pressure were measured. With the help of the stretching of the hoist and the calibration of the tensile dynamometer, the conversion relationship between the real-time strain value (ε_n) and the multi-directional trenching resistance (F_n) was determined as obeying the following:

$$F_n=10.94{\epsilon }_n-1039.26$$

(4)

Figure 13 shows the strain signals collected during the entire trenching operation. It was found that the forward resistance (F) after soil-engaging was significantly larger than others and had certain fluctuations. When the operation time reached 8.5 s, as the trenching depth reached 30 cm, the working state and forward resistance tended to stabilize. Therefore, the average force value corresponding to the 3 m stroke in the subsequent stable stage was calculated as the resistance index.

3. Results and Discussion

3.1. Analysis of the Simulated Trenching Process

The working status of the rotary tiller and furrowing plow in the combined trencher were extracted from the EDEM post-processing to analyze their respective interactions with soil particles. The soil disturbance during the rotary tillage process is shown in Figure 14a. It was found that with the forward feed, the effective cutting area involved multiple tillage layers within a depth of 0~30 cm. A large quantity of particles were thrown up to the rear and upper side along the tangential direction of the rake blade, indicating that rotary tillage has a strong transfer ability through particle throwing. This facilitates lateral transfer and soil accumulation after rebounding to the fender. The mixed distribution of particles after rotary tillage is completed is shown in Figure 14b, in which the mutual movement between layers is pronounced. The boundaries of the original tillage layer were disrupted relatively thoroughly, indicating that most of the cohesive bonds between particles were broken, making the soil soft and conducive to reducing the forward resistance of the subsequent furrowing plow.

The soil disturbance field induced by the furrowing plow at a cutting depth of 30 cm is shown in Figure 14c. During the advancement process, the particles are diverted along the curved surfaces on the left and right sides by the guide curve, so that the furrow bottom area with a longitudinal length of about 550 cm is clearly visible, forming a dynamic seed placement space that gradually moves forward. After the completion of the furrowing action, as shown in Figure 14d, it was found that the soil material originally accumulated on the side slopes had the effect of backfilling the furrow in a small amount, causing the seeding space to shrink. Therefore, sugarcane seeds should be sown before backfilling occurs so that they can be placed at the furrow bottom to reach the expected planting depth. In summary, the simulated trenching process indicates that the dynamic forming of seeding space was basically consistent with the trenching principle mentioned in the previous Section 2.2.2.

3.2. Analysis of the Simulated Trenching Resistance

The stress distribution on the furrowing plow surface during the trenching process is shown in Figure 15. For the plow tip that lifts the soil from the bottom, it is responsible for dividing and disintegrating the soil layers, so the bottom is subject to the greatest resistance. The upper curved surface serves to guide the soil upward with less resistance. The flat part at the top is subject to increasing stress as the soil in front continues to accumulate, until it stabilizes after 4 s. In addition, for the side guards, it is shown that the lateral pressure increases due to a large amount of soil being accumulated on both sides of the guard during stable trenching. This means that reinforcing ribs should be added between the guards to carry the inward force.

Under different configuration distances between the main rotary tiller and the furrowing plow of the combined trencher, the simulated trenching resistance and blade cutting resistance are shown in Figure 16a and Figure 16b, respectively. From the five sets of trials, it is clear that the trenching resistance increases with increasing the installation distance overall. The increase at the highest level of 89 cm is not obvious compared to the 78 cm level, which means that this is a critical point, after which the impact of rotary tillage on the trenching resistance tends to decrease. As for the cutting resistance of a single rotary blade, there is a gap in the alternating force results between different levels after 2.3 s. The cutting resistance generally decreases with the increase in the installation distance, which is exactly the opposite trend of trenching resistance. It is inferred that the smaller spacing between the rotary tiller and the furrowing plow allows for an increase in the amount of soil accumulated in the rotary area. And the blades repeatedly cut and throw the soil, which causes the power consumption for rotary tillage to increase. Due to the opposite trends of these two resistance characteristics, based on an estimated value of 7.5:1 in the energy consumption ratio they produced, L was determined to be an equal proportional value of 83.8 cm within its parameter range.

Under the three arrangements of the rotary blades, the simulated resistance and rotary power results as the number of blades per unit cutting sub-area change are shown in Figure 17. The average blade resistance decreased with increasing z, which could be inferred from Equation (2) to be related to the resulting decrease in the S, representing a decrease in the thickness of the soil cut by each blade. In comparison, Mode-2 had the lowest resistance to soil penetration and energy consumption for rotary tillage. It was analyzed to be related to the fact that Mode-2 had a thickness difference between adjacent cutting sub-areas equal to one quarter of S (illustrated in Figure 17b), so that Mode-2 allows multiple blades to successively cut into the soil. However, the difference in cutting thickness for both Mode-1 and Mode-3 is half the cutting pitch S.

3.3. Optimization of Furrowing Plow Parameters

The influence of the main design variables of the furrowing plow on the trenching resistance through orthogonal tests is shown in

Table 3. Orthogonal test results and range analysis of trenching resistance.

Trial No.		α	γ	Rc	F (N)
1		1	1	1	6026.67
2		1	2	2	6078.74
3		1	3	3	5916.68
4		2	1	2	6048.92
5		2	2	3	5952.03
6		2	3	1	6216.90
7		3	1	3	6148.45
8		3	2	1	6238.90
9		3	3	2	6260.50
F	$\overline{k_1}$	6007.36	6074.68	6160.82
	$\overline{k_2}$	6072.62	6089.89	6129.39
	$\overline{k_3}$	6215.95	6131.36	6005.72
	R	208.59	56.68	155.10

. The range analysis shows that the significant order of influence is the soil penetration angle, the curvature radius, and the oblique cutting angle. The ANOVA results in

Table 4. ANOVA of trenching resistance.

Source	DF	Sum of Squares	Mean Square	F-Value	p-Value	Sig
α	2	20,763.9	10,382.0	275.49	0.004	**
γ	2	235.7	117.9	3.13	0.242
Rc	2	6140.9	3070.4	81.48	0.012	*
Error	2	75.4	37.7
Total	8	27,215.9

Note: ** means that this item is extremely significant (p < 0.01), * means that this item is significant (p < 0.05).

also confirm this influential order. The relatively optimal parameter combination identified from the resistance performance of these groups in Table 3 is a soil penetration angle of 20°, an oblique cutting angle of 75°, and a curvature radius of 280 mm. The corresponding predicted trenching resistance value is the lowest 5,916.74 N.

3.4. Validation Analysis of Field Experiments

Using the rotary tiller arrangement, furrowing plow parameters, and configuration distance between components optimized by simulation, the field operation effect of the combined trencher is shown in Figure 18. As shown in Figure 18a, the actual measured soil-engaging stroke is about 1.46 m, which was not much different from the theoretically calculated value of 1.12 m, and the trajectory curve obtained by the movement of trencher is similar to the designed one. In addition, as shown in Figure 18b, the length of the effective seeding space formed is 53.8 cm, which is very close to the expected 55 cm. The error is mainly due to the small intrusion of rapid backfill soil into the dynamic space. And due to the lateral barrier function of the guard, the lateral width of the space has basically reached a tillage width of 40 cm, which is fully suitable for horizontal seeding.

The average planting depth of sugarcane seeds measured in the furrows excavated in Figure 18c is 29.5 ± 0.4 cm, the deviation range from the trenching depth of 30 cm is 1~3%, and the stability of long-row operations is good. It can also be seen that the cane seeds have been ideally arranged horizontally on the seed bed of crushed soil in the furrows. Therefore, it is comprehensively illustrated that the trenching and seed placement qualities of the designed combined trencher could meet the requirements of transverse deep planting of sugarcane, thus basically achieving precise transverse trenching. Meanwhile, the average resistance measured during trenching is 7609.7 N, and the error between the measured and predicted values under the same configuration is 22.2%, which is within the acceptable range due to the large number of clay blocks in the actual cultivated land.

4. Conclusions

(1)

A combined trencher structure was designed to address the issues of insufficient effective planting depth, soil backflow encroaching on the seeding space, excessive trenching resistance, and power consumption. The purpose is to effectively improve the stability and efficiency of trenching performance in the agronomic practice of the horizontal planting of sugarcane seeds. This machine and tool comprehensively utilized the soil lifting of the leak-proof plow, the soil fragmentation and throwing of the double-disc rotary tiller, the rebound of the fender, the lateral diversion of the furrowing plow, and the motion control of the double rocker arms. The working principle of trenching was proposed by using double-sided guards to block soil backfilling to form seeding space, and reducing the particle size and quantity of soil that could be acted upon in front of the plow face to reduce forward resistance.

(2)

The simulated trenching process showed that the designed rotary tiller had strong particle throwing and transfer capabilities to break bonds between particles. The dynamic seeding space was available during the gradual advancement process combined with the cooperation of the furrowing plow. The distribution of stress on the forward plow surface of the furrowing plow was analyzed. It was found that as the configuration distance between the rotary cultivator and the furrowing plow increased, the simulated trenching resistance and blade cutting resistance increased and decreased, respectively. Based on this, L was determined to be an estimated 83.8 cm. In addition, the cutting resistance decreased as the number of blades in the unit sub-area increases. The blade arrangement in Mode-2 with a quarter soil cutting pitch showed the smallest resistance and rotary tillage energy consumption.

(3)

The parameters of furrowing plow optimized to minimize trenching resistance were a soil penetration angle of 20°, an oblique cutting angle of 75°, and a curvature radius of 280 mm. Based on such a structural configuration, the soil-engaging trajectory of the trencher, the length and width of the accessible seeding space, and the average planting depth of sugarcane seeds could all reach their respective design expectations. The measured trenching resistance value was 7609.7 N, which had an error of 22.2% from the predicted value under the same configuration.