Optimal Design and Discrete Element Method Model Development of the Acute Angle Hoe Opener for No-Till System

Abstract

A specialized hoe opener was engineered for no-till systems to apply substantial amounts of wheat seeds and granular fertilizers, effectively suppressing early stage weeds. This distinctive hoe opener plants wheat seeds within a 120 mm wide horizontal band, positioning granular fertilizers precisely at the band’s center, all accomplished in a single pass. Notably, the design excels at covering the fertilizer with soil aggregates, compacting it through a wheat separator, and concurrently depositing wheat seeds from above. Our primary research objectives centered on achieving a consistent seedbed post-fertilizer application and ensuring a uniform distribution of wheat seeds within the horizontal band. The DEM (Discrete Element Method) was exploited to optimize the hoe opener’s parameters. Through extensive simulations and comparisons with experimental outcomes, an optimal wing orifice AB length of 60 mm was identified, effectively covering granular fertilizers with soil aggregates and achieving compaction through the wheat separator. Furthermore, parameters of the wheat seed separator’s hump were fine-tuned using the Box–Behnken algorithm, resulting in an optimal dimension of 40 mm for the top radius (A), 140 degrees for the top angle (B), and 90 mm for the bottom length (C).

1. Introduction

No-tillage represents an agricultural tillage approach designed to conserve crop residues on the ground surface. This method serves to keep the soil from destruction caused by wind and water, while also minimizing overall soil disturbance, except for specific activities such as sowing and tasks related to agricultural traffic [1,2,3,4]. In the immediate term, adopting no-tillage practices leads to higher moisture retention in the uppermost soil layer. However, it also brings about reduced soil aeration and increased mechanical resistance to the penetration of plant roots [5]. Despite the short-term effects, sustained implementation of no-tillage practices over a 15-year period in semi-arid regions with loamy soil has demonstrated notable improvements in soil properties. This encompasses an augmentation in water-retaining and aeration porosity, along with a substantial enhancement in water-holding capacity at a greater depth of 0.15 m. Furthermore, it has been observed that no-tillage practices can increase water withdrawal rates by up to 28% when compared to conventional tillage methods [6,7]. The fundamental goal of implementing a no-tillage system in wheat farming is to minimize or completely eliminate the necessity for traditional tillage practices. This approach aims to decrease both the time and costs associated with cultivation in wheat farming [8,9,10]. Furthermore, a comparative experiment illustrates that the no-till system stands out as the most energy-efficient option, showcasing a remarkable 77.9% reduction in carbon footprint compared to conventional tillage practices [11]. Nevertheless, this study indicates that achieving yields comparable to conventional tillage systems in no-till systems is feasible when effective weed control measures are in place. Without effective weed control measures, no-till systems could lead to reduced crop yields [12]. The application of herbicides post-emergence is a widely adopted method for effectively managing weed populations in wheat fields [13]. The incorporation of machine learning and artificial intelligence into precision agriculture enables customized weed management, which has the potential to decrease or eliminate the need for pesticides [14,15,16,17,18,19]. Nevertheless, alternative non-chemical strategies for weed control show promise. Such methods encompass utilizing certified seeds, growing crop varieties with weed resistance, employing mulching strategies, and implementing nutrient management practices that favor crop growth over weed competition [20]. The outcome of the competition between weeds and crops hinges on factors like the timing of their emergence, the maximum heights they reach, and their varying responses to additional nutrients [21]. Given the challenges outlined earlier, researching the operational mechanisms of seeders within the framework of no-tillage systems becomes imperative.

The approach of applying granular fertilizers alongside wheat seeds is closely tied to the functionality of the seeder’s working body. This often entails the utilization of a hoe or disc opener, enabling the concurrent application of fertilizers and seeds in a single pass of the seeder [22]. However, the placement of granular fertilizers is contingent upon the arrangement of wheat seeds. These fertilizers can be administered at an equivalent depth to the wheat seeds, either positioned centrally amongst a pair of wheat seeds or mixed with the seeds. It is important to note that, when applying fertilizers and wheat seeds, caution is advised against using high doses of fertilizers, as they may have the potential to harm germinating wheat seeds [23]. Therefore, to mitigate the risk of potential harm to wheat seeds, it is recommended to administer fertilizers and seeds of wheat at varying depths or positions [24]. Granulated fertilizers and seeds of wheat may be distributed at varying depths by employing either two separate disc colters or two distinct hoe openers. Another approach involves using a single hoe opener, where granular fertilizers are applied at a greater depth, followed by seeds of wheat at a shallower level at the same time. The selection of these methods should consider variables such as moisture in the soil levels and the amount of plant remnant on the ground surface [25]. The pair of separate hoe openers are positioned in a not aligned but rather offset position, to either the left or right margin. This arrangement amplifies the pulling force compared to an individual hoe opener [26]. Furthermore, considering that weed seeds commonly inhabit the ground surface, employing a pair of distinct hoe openers situated on various rows, as opposed to a single hoe opener, will lead to the burial of a larger number of weed seeds. Consequently, this may contribute to an augmentation in the quantity of weed seeds within the ground seed reserve [27,28]. Additionally, there are individual hoe openers engineered to deposit seeds simultaneously in a pair of rows while applying granular fertilizers between and at a greater depth than the seed level in a single pass. With this approach, there is no necessity to bury the fertilizer layer beneath the soil since the seeds are not directly placed on top of it. However, organizing seeds in rows decreases the distance between them, which could increase the competition among the seeds [29,30]. The coexistence of a pair of identical types competing for the identical scarce asset makes it impossible to attain stability [31]. Thus, in the conventional till system, wheat seeds are typically administered in a horizontal strip [32]. Nonetheless, distributing the seeds evenly across the horizontal band can mitigate intra-seed competition when sowing in this manner [33,34,35,36,37]. Moreover, uniformly applying a significant quantity of wheat seeds to the horizontal strip amplifies the superiority of the crop over weeds in competition, especially in situations wherein resource scarcity or environmental stress factors do not restrict the total biomass yield [38,39,40]. It is crucial to determine the ideal seeding density to prevent rivalry among the seeds. Generally, the method of depositing seeds in a horizontal band while placing granular fertilizer in a narrow strip beneath it entails the use of two separate hoe openers [41,42,43]. Taking into account the considerations mentioned earlier, the primary research objective was to design an innovative single hoe opener capable of simultaneously depositing seeds in a horizontal band while placing granular fertilizer in a narrow band beneath the seeds. Consequently, the initial research goal involved investigating the interactions between the soil and the newly designed hoe opener. The aim was to ensure the proper coverage of the granular fertilizer layer with soil particles, ultimately creating a compacted seedbed. The second research objective focused on examining the interaction between the wheat separator hump and the wheat seeds to achieve an even spread of seeds across the seedbed. The innovation in using the hoe opener lies in its ability to bury the fertilizer layer with soil, compact the soil, and simultaneously deposit wheat seeds from above.

2. Materials and Methods

The starting point for creating a hoe opener capable of simultaneously applying granular fertilizers and wheat seeds involved selecting a hoe opener designed for the application of either granular fertilizers or wheat seeds (Figure 1a) as the foundational working body. Subsequently, the development of the hoe opener for simultaneously administering seeds and mineral fertilizers took shape (Figure 1b). The foundational hoe opener comprises an opener tip (1), opener (2), trapezoidal pipe shank (3), cylindrical drum (4), and a delivery tube for granular fertilizer or wheat seeds (5). The opener tip (1) is connected to the opener (2) through two bolts, and the trapezoidal pipe shank (3) is welded to the opener (2). The cylindrical drum (4), set with a trapezoidal pipe shank and opener, is capable of rotating on the vertical axis in both directions to prevent blockage with crop residues. Its length and outer diameter are 200 mm and 40 mm, respectively. The delivery tube for granular fertilizer or wheat seeds (5) is welded to the hoe opener. In this study, the hoe opener was enhanced to simultaneously apply granulated mineral fertilizers and wheat seeds (Figure 1b). In the upgraded hoe opener for applying granulated mineral fertilizers and wheat seeds, the fertilizer delivery tube (6) is welded into the trapezoidal pipe shank. Before welding, an orifice is cut in the trapezoidal pipe shank, and the granular fertilizer delivery tube (6) is deformed to insert into the orifice. The granular fertilizer delivery tube (6) runs parallel to the wheat seed delivery tube (7), with the wheat seed delivery tube being welded to the hoe opener at a 30-degree angle. The outer diameter and thickness of the cylindrical tubes for delivering granular fertilizers (6) and wheat seeds (7) are 30 mm and 2 mm, respectively. The wheat separator (8) is welded to the trapezoidal pipe shank, along with the right and left opener wings (9), which are also welded to the opener (Figure 1c).

The development process of the hoe opener involved designing it in CAD software (version: 2021), and subsequently, the designed parameters were used to construct the physical hoe opener. Initially, the base hoe opener was cut according to the dimensions outlined in Figure 2a. The distances between the opener tip and opener bottom, and between the opener bottom and inclined cut, were set at 15 mm and 25 mm, respectively. The 35 mm distance represented the separation between the granular fertilizer layer and the wheat seeds layer. The inclined cut angle was chosen to be 20 degrees. In the second step, the wheat separator was welded to the trapezoidal pipe shank and opener, with its position determined based on the opener cut. The plain surface of the wheat separator (Figure 2b) was connected to the trapezoidal pipe shank from the bottom, moving upward parallel to the trapezoidal pipe shank. When the edge, limiting the upward motion, connected with the cut opener, the wheat separator stopped moving upward, establishing its position. At this point, the wheat separator was welded to the trapezoidal pipe shank and the cut opener. The wheat separator, with an outer diameter and thickness of 100 mm and 2 mm, respectively, was cut from a stainless-steel cylinder, and its plain surface was deformed. Other parameters of the wheat separator were determined as illustrated in CAD, in coordination with the developed hoe opener. Lastly, the right and left opener wings were welded alongside the cut opener, taking into account the opener cut and the position of the wheat separator.

When the developed hoe opener moves forward, it carves through the soil, allowing granular fertilizers to fall into their designated position within the narrow fertilizer layer (Figure 3a). However, if the soil is not compelled to fill the carved area, it can lead to a mixture of granulated mineral fertilizers and wheat seeds, causing an uneven application of wheat seeds at different depths. To address this issue, the opener wings feature orifices designed to ensure that the soil fills the carved area, covering the narrow fertilizer layer with soil. This feature is a novel aspect of the designed hoe opener (Figure 3b). The process of how the carved soil area is filled and how the soil entering the opener is compacted relies on the dimensions of the orifices. The objective was to apply granulated mineral fertilizers at a greater depth than the wheat seeds’ depth and create a flat, compacted seedbed for the wheat seeds (Figure 3c). The wheat separator plays a role in compacting the soil entering the opener through the orifice. The importance of the compacted seedbed lies in enhancing the contact between the soil and wheat seeds, thereby improving water supply maintenance for wheat seed germination under diverse environmental conditions [44,45,46].

Several parameters govern the design of the orifice, and the selection of the main parameters should eliminate the need for consideration of other factors. The three-sided pyramid-like form of the opener orifice, through which the ground penetrates, is illustrated in Figure 4a. Both ∠AOC and ∠AOB angles are set at a right angle. The angle of the left and right wings concerning the ground surface is determined by the ∠OAC angle, which remains constant at 45 degrees. The ∠BOC angle is contingent on the ∠BAC angle. A ∠BOC angle of less than 90 degrees increases the risk of the opener orifice being obstructed by plant stalks or stones. △AOD is a triangle perpendicular to the direction of tillage. In this design, where the ∠BAC angle is 90 degrees, the ∠BOC is 105 degrees (Figure 4b). Consequently, the edge of AC does not align at 90 degrees with the travel direction. Additionally, the margins of the right and left wings, marked as AC, are angled at 45 degrees. This specific design ensures that crop stems encountered alongside the hoe opener’s path either slide down along the sharp AC edge or are cut. Larger stones that cannot fit through the hoe orifice will also slide downwards.

Considering these design considerations, the dimension AB is deemed a critical factor affecting the measurements of the △AOC triangle. If the △AOC triangle is below the optimal level, the seedbed may not be flat or compressed. On the other hand, if the △AOC triangle is larger than optimal, more soil particles than necessary may enter through the opener orifice, potentially leading to the blockage of the granular fertilizer tube. A blockage in the granular fertilizer tube poses more significant challenges than leaving the carved soil area uncovered. An oversized △AOC triangle can potentially result in the blockage of the opener orifice, leading to increased draft force requirements for the hoe opener and the formation of an inadequate seedbed. Therefore, determining the optimal parameters for the orifice in the hoe opener is crucial, as they have a substantial impact on the tool’s performance.

2.1. Evaluation of Horizontal and Vertical Forces Applied by the Engineered Hoe Opener during Soil Interaction

The specific pulling force exerted by working bodies of the seeder relies on multiple factors, including the characteristics and state of the soil, tillage velocity, tiller type, configuration, soil resistance properties, share sharpness, tilling depth, hoe slice width, and the nature of the attachments utilized [47,48,49]. The orientations of both vertical and horizontal pressures were investigated to assess the impact of the engineered hoe opener design, and this was compared with the performance of the original, or base, hoe opener. In general, the horizontal force $\left(F_h\right)$ must oppose the direction of travel and the vertical force $\left(F_v\right)$ should be oriented upwards to aid in the penetration for significant soil loosening tasks [50]. Nevertheless, at the critical stand angle ${\alpha }_c$, the orientation of the vertical force shifts from downward to upward [51,52], as demonstrated in Figure 5. This critical angle for a plane steel hoe opener is expressed as follows:

$${\alpha }_c=\frac{\pi }{2}-\delta$$

(1)

where ${\alpha }_c$—the critical stand angle; $\delta$—the soil–stand friction angle ($\delta =22.5 \mathrm{degrees})$.

The alignment of vertical forces exerted on both the opener tip and opener wings is crucial for aiding in soil penetration, especially when the critical stand angles are below 67.5 degrees. These vertical forces not only impact the hoe opener but also influence the motion of the wheat separator, leading the hoe opener to move either downward or upward. The existing literature extensively explores how the dimensions and configuration of the tiller determine the trajectory of soil particles [53,54]. The existing literature encompasses discussions on both the tractive strength and the response of soil particles during their interaction with the fundamental hoe opener [55]. Vertical and horizontal strengths imposed by both the standard and the adapted hoe openers are investigated in the soil container utilizing a volumetric dynamometer unit.

2.2. The Experimental Methodology for Identifying the Optimal Parameters of the Hoe Orifice Using DEM

The DEM proves to be an adequate tool for simulating soil–soil and soil–hoe opener interactions [56].

In this study, the optimization of the designed hoe opener parameters was carried out by monitoring the positions of soil particles during their interaction with the hoe opener throughout the tilling experiment. Initially, to comprehend the necessity of incorporating an orifice into the hoe wings, a simulation experiment omitting the orifice was conducted. Subsequently, the optimal parameters for the hoe wing orifice were determined using DEM modeling through a single-factor experiment involving variations in the dimensions of AB (50 mm and 60 mm).

The simulation involved creating a soil box and a soil factory within the soil box. The dimensions of the soil box were set to 300 mm in width, 500 mm in height, and 1000 mm in length (Figure 6a). The soil factory, located at a height of 300 mm above the base of the soil box, was a surface generating soil aggregates arbitrarily. The distribution shares of the four soil aggregates were set at 25%. A designed hoe opener was inserted and placed near the middle of the soil box, positioned 50 mm above the bottom. Following the calibration of all DEM input parameters, soil aggregates commence with an initial velocity of 0.5 m/s (Figure 6b). Within 5 s, one thousand aggregates are deposited into the soil container, and connections between soil aggregates become operational based on the provided variables’ data (Figure 6c). The contact model of Hertz–Mindlin was utilized, where soil particles are bonded together, rendering the geometries of the soil aggregates less significant [57]. The theory of the contact model of Hertz–Mindlin is clearly described in the literature [58]. At the conclusion of the experiment, the ultimate overall height of the soil within the soil box measured 120 mm. During the trial, the designed hoe opener advanced at a velocity of 0.81 m/s, engaging in soil tillage (Figure 6d). The deformation of the ground was promptly analyzed following the passage of the designed hoe opener. The focal optimization parameter was to ensure that the hoe wing orifices effectively funneled soil aggregates inward to compact them using the wheat separator. The outcomes of the optimized hoe opener wing orifice parameters were validated through practical experiments conducted on a real soil bin. In this study, four types of soil aggregations, namely Column, Lump 1, Lump 2, and Nuclei, were deposited in the soil box (Figure 6e) [59].

2.3. Preparation of the Soil Bin

The soil bin experiment took place in a designated area measuring 10 m by 2 m. The soil comprised loamy clay with a granular composition, which had originated from parent loess [60]. The starting ground moisture was about 6%. To enhance soil moisture, water was progressively administered to the ground and incorporated using a rotary tiller. The moisture level of the ground was evaluated using an SU-LPC moisture meter manufactured by Beijing Mengchuangweiye Technology (Beijing, China). If the intended ground moisture level was not achieved, the process was repeated. Upon reaching the desired ground dampness, the soil bin area underwent compaction using a roller with dimensions of 0.6 m in diameter, 1.5 m in length, and a weight of 1000 kg. Compaction activities continued until the soil ceased to harden. Soil hardness, varying with soil depth, was recorded every 2.5 cm down to a specified depth of 18 cm using an SC900 compaction meter manufactured by Spectrum Technology (Brigend, UK). For this experiment, soil hardness was monitored up to a depth of 10 cm, as the hoe opener applied granular fertilizers and wheat seeds within this depth range.

2.4. Quantifying the Vertical and Horizontal Forces Exerted by the Hoe Opener

Figure 7 illustrates the volumetric dynamometer unit (VDU) employed in the soil bin experiment [61,62,63]. The TCC-2.1 pulling machine, manufactured by Heilongjiang Bona Technology (Harbin, China), facilitated the soil bin experiment. The pulling machine (1) was connected to the VDU (2) through a three-point hitch (3). The hoe opener (4) was affixed to the VDU. The tillage depth was adjusted to 10 cm by altering the three-point hitch of the towing equipment, measured from the tip of the hoe opener to the surface of the soil. The VDU consisted of bottom and upper frames. Bolts connected the three-point hitch to the upper frame, while the lower frame was linked to the upper frame using six load sensors, utilized for measuring vertical and horizontal forces. The vertical and horizontal forces were critical for comparing the new hoe opener with the base hoe opener. The horizontal force was determined by adding together the values from the left and right horizontal sensors, while the vertical force was calculated by summing the values from all three vertical sensors. As the towing equipment initiated the movement of the VDU at a speed of 3 km/h, the sensor data were sent to the main computer through the CAN bus system and then logged into an Excel file. The trial was conducted three times with varying soil moisture contents—10%, 20%, and 25%—to assess the impact of soil moisture. The outcome was determined by averaging the results of the triplicate experiments. The values of the base hoe opener were then compared with those of the designed hoe opener. In this study, the speed remained constant, as previous research indicated that an increase in speed led to a rise in draft force [64,65,66]. Given this study’s objective to compare basic and designed openers, a single speed was deemed adequate for the experiments.

2.5. Establishing the Positioning of Granular Fertilizers and Wheat Seeds

An experiment in a soil bin was carried out using a seeder to ascertain the locations where wheat seeds and granulated mineral fertilizers would be deposited (Figure 8). The designed hoe opener (1) was installed in the seeder frame (2) using the fixed parallel mechanical system (3). The parallel mechanical system stayed stationary. Wheat seeds and granulated mineral fertilizer were delivered to the hoe opener through the wheat delivery tube (4) and fertilizer delivery tube (5), respectively. Wheat seed and granulated mineral fertilizer tanks were affixed to the frame of seeder, and metering devices (6) measured the granular fertilizers and wheat seeds at the fertilizer tank (7) and wheat seeds tank (8). The rollers of the metering equipment were the same, with the working length and rotation speed set at the maximum values of 60 mm and 60 rpm, respectively [67]. Both metering devices were operated using a 12-volt battery (9) and operated remotely. To clearly identify the locations where wheat seeds and granular fertilizers were deposited, especially when high doses were applied, the frame of the seeder was linked to the towing machine (10) through the three-point hitch (11). The level of the wheat seeds was regulated by adjusting the height controller (12). The initial seeding depth was established at 6 cm. As the pulling machine commenced towing the seeder, the metering devices initiated the discharge of wheat seeds and granulated mineral fertilizers from the tanks to the hoe opener through the delivery tubes. The locations of the wheat seeds and granulated mineral fertilizer were established by excavating the soil till reaching the level of wheat seed and the level of granulated mineral fertilizer. The experiments were conducted in triplicate under three different soil moisture conditions—10%, 20%, and 25%—to establish the locations of the wheat seeds and granulated mineral fertilizer under varied circumstances.

2.6. Parameters of the Wheat Separator Hump in the Designed Hoe Opener and Experimental Procedure

The depiction of the utilized designed hoe opener is illustrated in CAD (Figure 9a). The hoe opener comprises three primary components involved in interacting with the wheat seeds: a circle-shaped tube made of PLA material (1), an ellipsoid-shaped tube made of steel (2), and a wheat separator hump made of PLA material (3). The ellipsoid-shaped tube has two circular sides to connect to the hoe opener and the circle-shaped tube (Figure 9b). It is produced by deforming the middle section of the circle-shaped tube having an inner diameter measuring 30 mm. The purpose of the ellipsoid-shaped tube is to guide the fallen wheat seeds to the center of the wheat separator. The wheat separator hump is positioned on the surface of the wheat separator made of steel (Figure 9c). The primary four parameters of the wheat separator hump are established as follows: α—wheat spreader inclination, degrees; β—top angle, degrees; R—top radius, mm; and L—bottom length, mm (Figure 9d).

The designed hoe opener was introduced into DEM to simulate its interaction with the wheat seeds. Six boxes, each with a width of 20 mm, were generated at the bottom of the hoe opener, positioned 20 mm apart, to collect the wheat seeds once the hoe opener was inserted into the DEM (Figure 10a). The factory of wheat seeds was placed inside and at the top of the circle-shaped tube to generate the wheat seeds (Figure 10b). After generation, the wheat seeds fall due to gravity, accelerating along the circle-shaped tube and ellipsoid-shaped tube [68]. As the wheat seeds pass through the ellipsoid-shaped tube, they interact with the wheat separator and wheat separator hump (Figure 10c). The wheat seeds either slide or roll on the surface of the wheat separator hump, ultimately falling into the designated boxes (Figure 10d). The mass of the wheat seeds in each box was measured, and the standard deviation of the wheat seed mass was calculated. These boxes were connected, with sizes of 50 mm in width, 150 mm in height, and 20 mm in thickness.

2.7. Procedure for Investigating Wheat Seed Behavior before and after Interaction with the Soil Plate

After establishing the parameters of the wheat separator hump in the DEM, the behavior of wheat seeds before and after interacting with the soil plate was investigated. For this purpose, a designed hoe opener was inserted, and a soil plate with a wheat factory was generated on the DEM to simulate the interaction between wheat seeds and the soil plate (Figure 11a,b). The dimensions of the soil plate were 1000 mm in length and 120 mm in width. Positioned beneath the hoe opener, the soil plate allows the wheat seeds exiting the hoe opener to fall directly onto its surface (Figure 11c). Once all preparations are complete, the wheat factory initiates the generation of 100 wheat seeds per second in an even distribution. Wheat seeds produced by the wheat factory take approximately 0.5 s to exit the hoe opener. As soon as the wheat seeds begin to leave the hoe opener, the hoe opener starts moving forward at a velocity of 0.81 m/s, allowing the wheat seeds to collect on the surface of the soil plate. It is important to note that the soil plate is virtual for the hoe opener. The wheat factory moves at the same speed and direction as the hoe opener, ensuring that the wheat seeds fall onto the surface of the soil plate. In this study, the soil plate serves as a representation of soil since the interaction between wheat seeds and a soil drum, which represents soil, was calibrated in a previous study [69].

3. Results

3.1. Input Parameters for Simulating Soil and Hoe Opener Interactions in DEM

The input parameters for simulating interactions between soil aggregates and steel in the DEM, as well as the input parameters for wheat seeds and granular fertilizers, are presented in

Table 1. Values extracted from the literature for modeling on DEM.

Input Characteristic	Numerical Representation	Corresponding Studies
Density of soil aggregates, (kg m−3)	1346	[59]
Poisson’s ratio	0.4
Shear modulus, (Pa)	1 × 106
Soil–soil restitution coeff.	0.2
Soil–steel restitution coeff.	0.3
Soil–soil static friction coeff.	0.4
Soil–soil rolling friction coeff.	0.3
Soil–steel static friction coeff.	0.5
Soil–steel rolling friction coeff.	0.05
Density of steel, (kg m−3)	7850	[59,70,71]
Poisson’s ratio	0.3
Shear modulus, (Pa)	8.23 × 1010

,

Table 2. Soil aggregates’ bonding characteristics [59].

Input Characteristic	Numerical Representation
Normal stiffness, (N m−1)	2,400,000
Shear stiffness, (N m−1)	1,700,000
Critical normal stress, (Pa)	235,000
Critical shear stress, (Pa)	186,000
Bonding start time, (s)	5
Bonded disc radius, (mm)	3.5

and

Table 3. Parameters for wheat inputs extracted from the primary literature for modeling on DEM.

Input Characteristic	Numerical Representation	Corresponding Studies
Wheat seed density of, (kg m−3)	1370	[69]
Wheat seed Poisson’s ratio	0.22
Shear modulus of the wheat, (Pa)	1.13 × 107
Wheat seed–wheat seed static friction coeff.	0.15
Wheat seed–wheat seed rolling friction coeff.	0.36
Wheat seed–steel static friction coeff.	0.40
Wheat seed–steel rolling friction coeff.	0.33
Wheat seed–PLA static friction coeff.	0.30
Wheat seed–PLA rolling friction coeff.	0.35
Wheat seed–soil plate static friction coeff.	0.51
Wheat seed–soil plate rolling friction coeff.	0.38
Wheat seed–wheat seed restitution coefficient	0.30	[72]
Wheat seed–steel restitution coefficient	0.30
Wheat seed–PLA restitution coefficient	0.30
Wheat seed–soil plate restitution coefficient	0.30

, respectively. These interaction properties have been calibrated based on the shape of soil particles found in the existing literature [59,70,71]. Additionally, the input parameters for wheat seeds and granular fertilizers have been calibrated to optimize the parameters of the wheat separator hump [69,72,73]. It is important to note that, in this study, the contact model of Hertz–Mindlin is exploited to replicate interactions between the soil and hoe opener. However, it is worth mentioning that other researchers have utilized linear cohesion and hysteretic spring contact models to calibrate the interaction properties of soil particles with varying moisture contents [74].

3.2. DEM Simulation Outcomes for Soil and Hoe Opener Interactions

The visual representation of deformed soil aggregates by the designed hoe opener is presented in Figure 12. The hoe opener’s wings, without an orifice, demonstrate that soil aggregates do not fill the carved soil area (Figure 12a). The absence of soil filling in the carved area could lead to the escape of wheat seeds and granulated mineral fertilizers. Additionally, the failure to fill the carved soil area may result in a significant variation in the depth of the wheat seeds, impacting their non-uniform germination. The hoe wing orifice directs soil aggregates into the hoe opener, and the carved soil area is adequately filled when the AB length of the hoe wing orifice is 50 mm and 60 mm (Figure 12b,c). However, it is essential to ensure that the seedbed is compacted to enhance the contact between wheat seeds and soil. With a 50 mm AB length in the hoe opener wing orifice, the moved soil aggregates did not provide sufficient volume to compact the seedbed. In the absence of soil compaction, the central part of the seedbed remains loose, causing variations in the depth of wheat seeds when compacted by wheels. On the other hand, with a 60 mm AB length in the hoe opener wing orifice, the volume of soil aggregates moved into the carved soil area was adequate for seedbed compaction. Further increases in the AB length of the hoe opener wing orifice did not offer additional benefits. These simulations were conducted without considering the impact of the wheat separator to observe the behavior of soil aggregates based on orifice parameters.

The impact of the wheat separator on seedbed compaction with a 60 mm AB length is depicted in Figure 13. To analyze the behavior of soil aggregates when interacting with the hoe opener, the color of soil aggregates changes based on their speed of movement, revealing the deformed soil structure (Figure 13a). The color differentiation represents the speed of soil movement along the z-axis, aligned with the direction of the hoe opener. This visualization illustrates that the change in color around the moving hoe opener not only carves the soil but also propels soil particles forward due to the friction between the hoe opener and the soil. A specific area of the soil is selected for a detailed examination of soil aggregate behavior near the hoe opener, with a vector indicating the direction of soil movement (Figure 13b). As the hoe opener advances and reaches the selected soil area (Figure 13c), the behavior of soil aggregates within the hoe opener becomes visible from the rear, with reduced opacity in the wheat separator (Figure 13d). The alteration in color and direction of the soil aggregates indicates that the moving hoe opener guides soil particles into the hoe opener through the left and right-wing orifices, filling the carved soil area. It is important to note that the soil aggregates entering the orifices are already deformed by the hoe opener during soil carving. The shift in color in the soil aggregates inside the hoe opener, from yellow to bluish, signifies an acceleration in the forward movement speed as they interact with the wheat separator. The wheat separator moving forward changes the direction of the soil particles and moves them downside [40]. The compaction of the seedbed with the wheat separator becomes evident when the soil aggregates return to their default view on DEM (Figure 13e).

3.3. Comparison of Horizontal and Vertical Forces Exerted by the Base and Modified Hoe Openers across Different Soil Moisture Levels

The experimental outcomes from the soil bin, which assessed the horizontal and vertical forces of both the base and new hoe openers utilizing the volumetric dynamometer unit, are outlined in

Table 4. Forces influencing the base and designed hoe openers at various soil moisture conditions.

	Moisture of Soil, 10%		Moisture of Soil, 20%		Moisture of Soil, 25%
	Designed, N	Base, N	Designed, N	Base, N	Designed, N	Base, N
Horizontal left	124 ± 3	142 ± 1	126 ± 4	1038 ± 61	1339 ± 21	−110 ± 9
Horizontal right	189 ± 18	122 ± 16	742 ± 21	−268 ± 2	−262 ± 4	1058 ± 47
Horizontal	314 ± 18	265 ± 17	869 ± 26	770 ± 61	1076 ± 26	948 ± 40
Vertical 1	268 ± 5	239 ± 5	497 ± 5	247 ± 20	431 ± 16	582 ± 21
Vertical 2	494 ± 16	571 ± 6	87 ± 6	218 ± 31	−82 ± 45	−57 ± 42
Vertical 3	96 ± 6	64 ± 7	388 ± 13	484 ± 25	618 ± 9	355 ± 27
Vertical	859 ± 15	875 ± 5	972 ± 11	950 ± 14	967 ± 19	880 ± 6

. The designed hoe opener was scrutinized in comparison to the base hoe opener across varying soil moisture levels. A maximum soil moisture content of 25% was chosen due to concerns about the soil becoming sticky during compaction with the drum at higher moisture levels. The total horizontal force was computed by summing the forces from the right and left sides, while the total vertical force was calculated by summing forces from three different vertical sensors. Soil moisture exhibited a pronounced impact on horizontal force, but not on vertical force. Horizontal forces increased for both hoe openers with rising soil moisture. However, the horizontal force of the designed hoe opener surpassed that of the base hoe opener across all soil moisture conditions. This difference was attributed to the presence of hoe opener wings and a wheat separator in the designed hoe opener, introducing additional friction [75]. The vertical force exerted by the hoe opener wings was directed downward, while the vertical force from the wheat separator was directed upward. Consequently, the vertical force generated by the designed hoe opener exceeded that of the base hoe opener when the soil moisture was at 20% and 25%, but was less pronounced at a 10% soil moisture. It is hypothesized that, in the compaction of dry soil, the top layer retains a softer consistency compared to the deeper layers. Conversely, in the compaction of wet soil, the upper layer becomes harder than the deeper layers (Figure 14). The upper layer of the soil exhibited greater hardness when the soil moisture was at 25% than at 20%. This observation confirms that the vertical force applied by the hoe opener was directed upward, resulting in less vertical force for the base hoe opener when the soil moisture was at 25% compared to 20%. Previous studies have explored experiments aiming to reduce tiller draft force by narrowing the tiller width [76,77,78]. Nevertheless, this study specifically aimed to reduce the planter draft force by utilizing a single hoe opener while simultaneously applying granular fertilizers and wheat seeds at different depths. It is noteworthy that the fuel consumption of tractors was not taken into account in this research, as prior studies have established that a reduction in draft force leads to decreased fuel consumption [65,79,80]. If we regard the horizontal force as a draft force, the fuel consumption of the designed hoe opener would be lower than when using two base hoe openers. It is important to note that these findings were obtained at a tilling velocity of 0.81 m/s, and the impact forces may vary with changes in tilling speed. The increase in the tilling speed increases the draft force [77].

3.4. Granular Fertilizers and Wheat Seeds Positioning Depending on Soil Moisture

The location of the wheat seeds and granulated mineral fertilizers applied by the designed hoe opener at different soil moisture levels are shown in Figure 15. Mixtures of granular fertilizers and wheat seeds did not occur at any soil moisture. The distance between granulated mineral fertilizers and wheat seeds varied in the range of 30–35 mm. At soil moisture levels of 10 and 20%, soil deformations were less pronounced than at a soil moisture level of 25%. Due to the hygroscopic characteristics of the granular fertilizer, the position of the granular fertilizer was evident when scraping the soil, as the granular fertilizer became liquid and changed the color of the soil. The wheat separator compacted the soil, moved into the hoe opener, and created an even seedbed, and the wheat seeds were placed on the even and compacted seedbed. At 25% soil moisture, it was easy to determine the position of wheat seeds, since the sizes of the compacted soil aggregates covering wheat seeds were larger than the soil aggregates under conditions of 10% and 20% soil moisture. During the experiments, the number of wheat seeds in the middle was greater than at the edges of the seedbed. To address this, the parameters of the wheat separator hump must be further optimized for an even distribution of the wheat seeds on the seedbed.

3.5. Results and Analysis of the Wheat Separator Hump Parameters

The levels of the wheat separator hump parameters to optimize based on the Box–Behnken design are shown in

Table 5. The Box–Behnken design to optimize the wheat spreader hump parameters.

Factor	Name	Unit	Minimum Level	Maximum Level
A	Top radius (R)	mm	30	50
B	Top angle (β)	degrees	135	145
C	Bottom length (L)	mm	80	90

. The levels were determined by initially provided simulation experiments on DEM. Initially, four factors influenced the behavior of the wheat seeds. However, based on previously provided DEM simulation results, three factors were chosen for the experiment. α—wheat spreader inclination was considered as an exclusion factor and was chosen to be 17.5 degrees. If the wheat spreader inclination is less than 17.5 degrees the wheat seeds will easily stop on the surface of the wheat separator hump, causing the wheat seeds to accumulate on the surface of the wheat separator hump. It is believed that this phenomenon is caused by the shape of the wheat seeds formed on the DEM with a sphericity of 60% [69]. If the sphericity of the particles was close to 90%, the particles would rotate rather than slide [73,81]. If the wheat spreader inclination exceeds 17.5 degrees, the levels of other factors are limited.

The experimental results to determine the wheat spreader hump’s optimal parameters are shown in

Table 6. Experiment results to determine the wheat spreader hump parameters.

	A	B	C	Box Order, g						Σ	Standard Deviation
				1	2	3	4	5	6
1	30	135	85	22.10	48.00	31.00	28.40	41.40	34.50	205.40	9.30
2	50	135	85	20.10	36.80	41.90	42.30	39.80	26.30	207.20	9.20
3	30	145	85	19.77	50.90	26.70	26.30	54.80	29.20	207.67	14.52
4	50	145	85	15.38	42.80	39.00	41.60	49.10	20.30	208.18	13.56
5	30	140	80	14.72	56.10	26.20	27.20	54.80	28.60	207.62	16.89
6	50	140	80	13.77	43.60	39.30	41.50	50.40	16.99	205.56	15.12
7	30	140	90	28.40	40.60	28.60	29.20	44.80	34.30	205.90	6.97
8	50	140	90	19.11	41.20	41.00	41.50	40.30	25.20	208.31	9.93
9	40	135	80	16.55	46.10	33.90	35.70	48.60	25.50	206.35	12.15
10	40	145	80	16.33	47.10	33.00	34.30	55.70	20.70	207.13	15.04
11	40	135	90	24.20	36.30	37.70	39.00	39.50	28.90	205.60	6.26
12	40	145	90	20.40	44.50	33.20	33.80	49.10	26.90	207.90	10.69
13	40	140	85	22.10	42.40	37.60	35.60	40.30	27.80	205.80	7.81
14	40	140	85	22.90	38.10	39.30	34.10	41.10	30.40	205.90	6.80
15	40	140	85	24.80	43.70	34.90	38.00	38. 20	26.00	205.60	7.44

Note: Σ shows that Sum of box order items 1–6.

. The sum of the wheat seed mass in six boxes varied little but was considered to be eliminated. The standard deviation in the wheat seed mass was calculated by collecting wheat seeds in six boxes. The purpose was to minimize the standard deviation of the wheat seed mass falling to the boxes.

The ANOVA of the determination of the optimal parameters of the wheat separator hump shows the model to be extremely significant (

Table 7. ANOVA of the determination of the optimal parameters of the wheat spreader hump.

Source	Sum of Squares	df	Mean Square	F-Value	p-Value
Model	166.23	9	18.47	15.86	0.00 **
A	0.00	1	0.00	0.00	0.97
B	35.70	1	35.70	30.66	0.00 **
C	80.33	1	80.33	68.99	0.00 **
AB	0.18	1	0.18	0.16	0.71
AC	5.59	1	5.59	4.80	0.08
BC	0.59	1	0.59	0.51	0.51
A2	26.26	1	26.26	22.56	0.01 *
B2	8.03	1	8.03	6.90	0.05 *
C2	15.62	1	15.62	13.42	0.01 *
Residual	5.82	5	1.16
Lack of Fit	4.24	3	1.41	1.78	0.38
Pure Error	1.59	2	0.79
Cor Total	172.05	14

R² = 0.96; Adj R² = 0.90; Pred R² = 0.58; Adeq precision = 12.70; CV = 9.98%. Note: * shows that the item is significant (p < 0.05); ** shows that the item is extremely significant (p < 0.01).

). The top radius (A) in the model is not significant. We assume that this is because the distance between the minimum and maximum levels was little to determine the effect. Nevertheless, the levels were determined by initial experiments conducted on DEM. The increase in A would direct the wheat seeds to the middle of the seedbed and the decrease would direct the wheat seeds to the edges of the seedbed. It is believed that the standard deviation is not an adequate response to determine the direction of the fallen wheat seeds, as it does not estimate the order of the boxes, but is an adequate response to compare the various configurations of wheat separator hump parameters. The top angle (B) and the bottom length (C) were extremely significant in the model. The increase in B and the decrease in C would minimize the standard deviation (Equation (2)). The optimized parameters of the wheat separator hump A, B, and C are 40 mm, 140 degrees, and 90 mm, respectively (Figure 16). Experimenting on DEM with these parameters decreased the standard deviation to 5.40.

$$\mathrm{St}.\mathrm{dev}=2.11\mathrm{B}-3.17\mathrm{C}+2.67{\mathrm{A}}^2+1.47{\mathrm{B}}^2+2.06{\mathrm{C}}^2$$

(2)

3.6. Wheat Seed Behavior before and after Interacting with the Soil Plate

After determining the wheat separator hump parameters, the wheat behavior was examined before and after interacting with the soil plate. To examine the wheat seed behavior, the velocity and falling direction of the wheat seeds were compared when the hoe opener was not moving and when it was moving forward (Figure 17a,b). When the hoe opener was not moving, the falling direction of the wheat seeds inside the tube and on the wheat separator hump surface was parallel to the interacting surface. This shows that the wheat seeds are sliding or rotating on the interacting surface and, in the end, the wheat seeds leave the hoe opener with some velocity. When the hoe opener was moving forward with a velocity of 0.81 m/s, the falling direction of the wheat seeds shifted to the hoe opener’s moving direction. This happened because the wheat factory moves forward with the hoe opener with the same velocity and direction and the initial velocity of the generated wheat seeds will coincide with the hoe opener velocity. The wheat seeds interacting with the wheat separator move back relative to the hoe opener and when the wheat seeds leave the hoe opener the velocity of the wheat seeds will be lower than the hoe opener velocity. At the velocity of 0.81 m/s of the hoe opener, the wheat seeds were still moving forward. This shows that, when the wheat seeds leave the hoe opener, the wheat seeds will rotate or slide on the soil surface forward direction until stopping [82]. This phenomenon is a common problem for seeders. To prevent this, it is recommended to cover seeds with soil when the seeds leave the hoe opener so that the wheat seeds become stuck where they fell between the soil particles [82].

The influence of the optimized wheat separator hump was determined by comparing the hoe opener with and without the wheat separator hump (Figure 18a,b). The wheat seeds fell to the middle side of the soil plate when the hoe opener was without the wheat separator hump. However, the wheat seeds were distributed along the soil plate when the hoe opener was with the wheat separator hump. There were wheat seeds gathering on the soil plate because the hoe opener increased its velocity instantly on DEM. This shows that the instant change in velocity influences the wheat seed distribution in the soil.

4. Conclusions

A specially designed hoe opener was created to distribute granular fertilizer and wheat seeds concurrently at two distinct levels, with the fertilizer positioned below the seeds, across a 12 cm wide flat seedbed. To ensure that the granular fertilizer was deposited deeper than the wheat seeds, openings were incorporated into the wings of the hoe opener to accommodate the fertilizer layer, guiding the soil toward the center from both sides. The innovation in using the hoe opener lies in its capability to bury the fertilizer layer beneath the soil, compact the soil, and simultaneously deposit wheat seeds from above. The parameters of the hoe opener wing orifice were optimized using the DEM software (version: 2022). The ideal length for the hoe opener wing orifice, AB, was found to be 60 mm through real experiments conducted in a soil bin using a volumetric dynamometer unit, across various soil moisture levels. The wheat separator compressed the soil, ensuring a uniform seedbed and evenly distributing the wheat seeds across a 12 cm wide area. The results of the volumetric dynamometer unit show that the draft force of the designed hoe opener was larger than the base hoe opener in all soil moisture conditions, but the vertical force of the designed hoe opener was greater than that of the base hoe opener when the soil moisture levels were 20% and 25%.

To distribute wheat seeds on the seedbed evenly, the wheat separator hump parameters were optimized. Initially, the main four parameters of the wheat separator hump of the wheat separator were determined: wheat spreader inclination (α), top angle (β), top radius (R), and bottom length (L). The wheat spreader inclination (α) was determined to be 17.5 degrees based on previously provided simulations on DEM. The other parameters such as top angle (β), top radius (R), and bottom length (L) of the wheat separator hump were optimized based on Box–Behnken design at 40 mm, 140 degrees, and 90 mm, respectively. Experimenting on DEM with these parameters decreased the standard deviation to 5.40.

The compaction of the wheat seeds after being covered with the soil is drastic. Therefore, the shape of the compacting wheel and pressure should be further investigated. We recommend using ring spurs to compact the soil. Thus, the surface of the soil remains loose, and the deeper side is compacted.