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Article

Effects of Wet Soybean Dregs on Forming Relaxation Ratio, Maximum Compressive Force and Specific Energy Consumption of Corn Stover Pellets

by
Tianyou Chen
1,2,
Wenyu Zhang
2,
Yuqiu Song
2,* and
Yanlin Wang
1
1
School of Mechanical and Electrical Engineering, Lanzhou University of Technology, Lanzhou 730050, China
2
College of Engineering, Shenyang Agricultural University, Shenyang 110866, China
*
Author to whom correspondence should be addressed.
Agriculture 2025, 15(16), 1727; https://doi.org/10.3390/agriculture15161727
Submission received: 3 June 2025 / Revised: 5 August 2025 / Accepted: 5 August 2025 / Published: 11 August 2025
(This article belongs to the Special Issue Valorization of Agri-Food Waste Bioresources for Sustainable Livestock Feeding)
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Abstract

This study aims to explore the influence mechanism of wet fermented soybean dregs on corn stover formation, improve the forming quality of straws and reduce the power demand and specific energy consumption of forming equipment. This study takes 2 mm and 4 mm corn stover sizes as the objects and explores the influence of different amounts of fermented soybean dregs on the volume relaxation ratio, maximum compressive force and specific energy consumption of straw forming pellets under compression displacements of 90 mm and 92 mm. Different amounts of water are selected according to the total moisture content of the mixed feed, and the effects of adding water and fermented wet soybean dregs on feed forming are compared and studied. The results indicate that, under certain conditions, adding water or wet fermented soybean dregs to straw is beneficial for shaping. Adding wet fermented soybean dregs to straw can improve the nutritional value of feed and promote the utilization of agricultural waste. Therefore, adding wet fermented soybean dregs is an effective method for processing high-quality feed pellets. Taking into account the quality and specific energy consumption of mixed feed processing, the optimal pelleting process for corn stover and wet fermented soybean dregs in a mixed feed is as follows: straw particle size of 4 mm, added mass ratio of wet fermented soybean dregs of 5% and compression displacement of 92 mm. These results support the research and development of technology and devices for high-quality and low-energy mixed formation using fermented soybean dregs and straw, and they offer a new route for the utilization of other high-moisture feeds.

1. Introduction

Crop residue is an important renewable resource. Every year, a huge quantity, more than 5 billion megagrams of agricultural residue, is produced globally [1]. China is rich in crop straws; the total national output of crop straws was nearly 900 million tons in 2020 [2]. Straws are mainly composed of cellulose, hemicellulose and lignin, and they can be used as feeds, fuels and so on. However, the looseness and wide distribution of straws make their transport and storage inconvenient [3]. Densification is the easiest and most effective method to solve the low density of straws. Moreover, granulation can improve the palatability of straws and increase the feed intake, digestibility and daily weight gain of animals. These techniques also effectively solve the problems of seasonal and annual supply–demand imbalance, high transportation and storage costs and time-consuming and labor-intensive feeding of feeds, and they are the key to promoting the development of intensive, large-scale and grain-saving breeding [4,5]. Straws are limited by poor bonding, low forming quality, a large power demand for equipment, high energy consumption and a low feed utilization rate [6].
The existing research utilizes additives and forming processes to achieve high-quality and low-consumption forming of materials. Gageanu et al. found that adding corn starch and beets improved the durability of alfalfa, wheat and rapeseed straw-formed pellets [7]. Obidzinski et al. showed that the density of formed pellets increased when 10% potato slurry was added to buckwheat husk [8]. Matkowski et al. showed that the density of wheat straw-formed pellets was maximized after the addition of 4% cassava starch or calcium carbonate [9]. Chojnacki et al. studied the effects of fruit pomace and vegetable residues on the hardness and density of barley straw pellets, and they found that the residues improved the quality of straw pellets [10]. Miladinovic et al. found that the addition of enzymes, xylanase and phytase in degreased microalgae reduced the flow resistance of raw materials in the mold and decreased the energy consumption of material formation [11]. Guo et al. reported that the addition of potato slag contributed to straw formation and decreased the relaxation ratio of pellets [12]. In terms of the forming process, the influences of the moisture content, particle size and compression force on straw formation have been explored. When the compression force was enhanced, the relaxation density and durability of the particles increased, but energy consumption rose accordingly [13,14]. Generally, straws with a smaller particle size can be more easily formed, and the density and durability of the formed pellets are greater [15]. Hou et al. showed that the forming effect was better for 5–8 mm corn stover at a moisture content of 8–12% [16]. Wang et al. found that the relaxation density of formed pellets declined as the water content in 16–100-mesh corn stover rose from 8–24% [17]. Ding Ning et al. concluded that the optimal forming moisture content of chopped corn stalks was 24.26% [18]. Hence, the optimal moisture content of straws varies with the variety and particle size.
Soybean dregs are the by-product of soy product processing [19], with an annual output of over 20 million tons [20]. Soybean dregs are rich in dietary fibers, proteins, lipids, vitamins and minerals, and they have high nutritional value. However, the high moisture content (>75%) and rich nutrients of fresh soybean dregs are suitable for the breeding and habitation of microorganisms. Hence, fresh soybean dregs are extremely prone to decay and deterioration, and they cannot be stored for long time, affecting their high quality and efficient use. Fermentation can decrease the anti-nutritional factors affecting soybean dregs. Fermented soybean dregs can be easily digested and absorbed by animals and are a substitute for soybean meal and other protein feeds. Nonetheless, inappropriate storage will induce mildewing [21,22]. Currently, only 10% of soybean dregs are processed and used, but abundant soybean dregs are applied in fertilizers or discarded, which causes severe waste [23].
In summary, the moisture content of straw and the type of added material affect the pelleting effect of straw. After being crushed, transported and stored, the moisture content of straw is relatively low, lower than the optimal moisture content for straw pelleting [12,24]. Generally, wet soybean dregs need to be stored and transported, a process that takes a long time. Due to their high moisture content, wet soybean dregs are prone to spoilage and have a low utilization rate. Therefore, it is necessary to ferment wet soybean dregs. Fermented wet soybean dregs can be stored for long time. Mixing straws with fermented wet soybean dregs can provide moisture for feed pelleting. In addition, granulation of wet fermented soybean dregs mixed with straws can improve the nutritional value of feed, and it has great potential for development and utilization, making it an effective method for processing feed pellets. The mixed and extruded feed pellets can be used by ruminant animals such as cattle and sheep.
Our preliminary research results indicate that adding wet soybean dregs can significantly improve the molding quality of corn stover [24], but the impacts of adding wet soybean dregs on the maximum molding force and specific energy consumption of stover are still unclear. Moreover, the existing research cannot provide any reference. Herein, the effects of adding wet-fermented soybean dregs versus water on the volume relaxation ratio, maximum compressive force and specific energy consumption of corn stover formation were comparatively studied, aiming to clarify the effects of fermented soybean dregs on corn stover formation. This study will support the optimization of a mixed soybean dreg and corn stover high-quality and energy-saving formation process and instruments and offers a new route for the utilization of high-moisture feeds.

2. Materials and Methods

2.1. Materials and Treatment

Fresh soybean dregs were bought from a tofu processing factory (Shenyang Agricultural University Tofu Processing Factory, Shenyang, China), and a fermentation agent for soybean dregs (Wangnongbao Biotechnology Co., Ltd., Zhengzhou, China) was added at a ratio of 1 mL: 1 kg. The microbial strain of the fermentation agent is Enterococcus faecalis, which had greater than 2 × 106 CFU/mL. According to the instructions of the fermentation agent, after adding the fermentation agent and fermenting the mixture under anaerobic conditions for 3–5 days, a sour taste can be smelled, indicating that the fermentation is complete and it can be used. Generally, fresh soybean dregs need to be fermented, transported and mixed with straws for pelleting. Therefore, this study chose a fermentation time of 10 days for wet soybean dregs. The fermented soybean dregs had a moisture content of 80%. As for the nutrient composition, the air-dried fermented soybean dregs were composed of 91.86% dry matter, 88.22% organic matter, 17.23% crude proteins, 4.85% crude fats, 36.15% neutral detergent fibers and 17.78% acidic detergent fibers. For feed pellets, the required straw particle size is usually smaller than 5 mm [25]. Hence, the corn stover (variety: Suyu28) was crushed in a pulverizer, and then it was screened using 2 or 4 mm sieves. The resulting straws contained 8% water.

2.2. Methods

2.2.1. Instruments and Program

A feed molding test device (Figure 1) is composed of a pressure head, a mold (inner diameter: 20 mm, height: 103.5 mm), a plug plate, a base, etc. The pressure head is connected to a microcomputer-controlled electronic universal testing machine (model: WDW-200, Jinan Shijin Group Co., Ltd., Jinan, China). In the forming process, feeds were added to the mold, and then the universal testing machine was started and operated at a rate of 100 mm/min. When the preset displacement was reached, it was held for 30 s [26]. Then the plug plate was rapidly removed manually, and the formed pellets were pushed out at the rate of 180 mm/min. Finally, the indenter returned to the initial position.

2.2.2. Design and Execution of Experiments

Wet fermented soybean dregs are composed of dry matter and water. In order to investigate the influences of wet fermented soybean dregs on the molding effect and rheological parameters of corn stover under different straw particle sizes and compression conditions, the study included the following experimental parameters. Preliminary experiments found that, when the compression displacement was less than 90 mm, the quality of feed molding was poor and even non-molding occurred. When the compression displacement was greater than 92 mm, the molding effect of feeds did not show significant improvement, while the maximum molding force and energy consumption significantly increased. Therefore, this study included feed compression displacements of 90 mm and 92 mm. As mentioned earlier, for the raw materials of feed particles, the straw particle size is generally required to be less than 5 mm [25], and this study includes particle sizes of corn stover of 2 mm and 4 mm. For the 2 mm straws, the compression displacements of 90 and 92 mm were marked as T11 and T12, respectively. For the 4 mm straws, the compression displacements of 90 mm and 92 mm were marked as T21 and T22, respectively. Generally, when the moisture content of feed exceeded 25%, the molding quality was poor. Meanwhile, for ruminant animals, the addition of 5% to 24% soybean dregs in the diet had a negative impact on their DM intake or productivity [27,28,29,30]. Therefore, this study comprehensively considered the effects of feed molding and animal feeding, and the addition levels of fermented wet soybean dregs were 0%, 5%, 10%, 15%, 20% and 25%, with 0% as the control group. To compare and explore the effects of feed moisture content and fermented wet soybean dregs on molding, it was necessary to prepare feeds with a consistent moisture content. Therefore, the amount of water added was determined separately through calculation.
The mass of straws for each test was determined in pretests to be 4 g. The corn stover samples of 4 g (8%, w.b.) at sizes of 2 mm and 4 mm were weighed with electronic scales (BS200S, Sartorius, Gottingen, Germany) and sealed in bags. The wet fermented soybean dregs of 0.2, 0.4, 0.6, 0.8 or 1.0 g were weighed and evenly added to the corn stover samples of 2 and 4 mm separately. Then the mixtures were blended and placed in sealed bags to obtain mixed feed samples (the added levels of fermented soybean dregs were 5%, 10%, 15%, 20% and 25%). The mixed feed samples were keptfor 48 h at room temperature. For the control group (0% soybean residue), only 4 g of straw was packed in a sealed bag for testing. For the straws that needed water regulation, 4 g of straws was weighed. Then the straws of each group were sprayed with 0.15, 0.31, 0.45, 0.60 and 0.74 g of water separately. Next, the mixtures were blended manually and sealed in bags for 48 h to make the water evenly distributed. Each treatment was replicated six times. The study was conducted in 2023.

2.2.3. Detection Indices and Methods

(1)
Volume relaxation ratio
In the existing research, the ratio of ‘compression density’ to ‘relaxation density after 5 h of placement’ is used to reflect the forming effect of materials [12,31]. The mass changes little in the placement, and the change is mainly attributed to volume relaxation. Wang Ruili et al. measured the forming effect using the volume relaxation ratio [32]. This study showed that the size of the formed pellets stabilized after 7 days of storage, so the volume relaxation ratio can be used as an indicator, which can be calculated according to Equation (1):
S r = V V 0 × 100 %
where Sr is the volume relaxation ratio; V0 is the compression volume, m3; V is the relaxation volume, m3. A smaller relaxation ratio means the material has a better forming effect.
(2)
Maximum compressive force
The force during feed formation can be tested, recorded and saved in real time using a universal testing machine, and the maximum compressive force of the material can be obtained through screening.
(3)
Specific energy consumption
Specific energy consumption refers to the energy required for straw formation per unit mass, and it is one important indicator for evaluating the cost of material densification. It consists of specific energy consumption for compression and specific energy consumption for extrusion and can be calculated according to Equation (2) [33]:
E m = ∫ 0 x 1 F 1 ( x ) d x + ∫ 0 x 2 F 2 ( x ) d x m
where Em is the specific energy consumption of formation, J/g; F1(x) and F2(x) are the forces of compression and extrusion, respectively, at different positions, N; x1 and x2 are the positions of the indenter during the compression and extrusion, respectively, m; m is the dry matter mass of the material, g.

2.2.4. Data Analysis

Data were analyzed using SPSS 26.0. General linear models were used to analyze the influence degrees of experimental factors and interactions on indicators. The comparative mean method was used to analyze the differences in the average values of indicators within the group under different addition levels of moisture or wet fermented soybean dregs. The differences were compared by Duncan’s range test at a significance level of 5%. Data were expressed as mean ± standard deviation (SD), and figures were generated using Origin 8.0.

3. Result Analysis and Discussion

3.1. Volume Relaxation Ratio

3.1.1. Effect of Moisture on Volume Relaxation Ratio of Straw Formation

Analysis of variance was conducted with the experimental data of the volume relaxation ratio of straw molding under water addition conditions, and the results are shown in Table 1. According to Table 1, the straw particle size, compression displacement and water addition mass all have an extremely significant impact on the volume relaxation ratio of feed pellets. The interaction between straw particle size and water addition mass and the interaction between compression displacement and water addition mass both have an extremely significant impact on the volume relaxation ratio of feed pellets. The interaction between straw particle size and compression displacement has a significant impact on the volume relaxation ratio of feed pellets. The effects of moisture on the volume relaxation ratio of straw formation are shown in Figure 2. For the 2 mm straws, the volume relaxation ratio first increased and then dropped with the rising water addition, and it was minimized when the water addition was 0.15 g (water content of 11.33% in straws) (Figure 2). Compared to straws without water addition, significant differences were observed in the volume relaxation ratios; specifically, the relaxation ratios at 90 mm and 92 mm compression decreased by 9.23% and 8.06%, respectively. For the 4 mm straws, as the water addition increased, the relaxation ratio increased, then decreased and increased again. There was no significant difference in the volume relaxation ratio of straw formation from 0–0.45 g of water addition. The reason is that the optimal forming moisture content varies with the particle size of straws. When the moisture content exceeds the optimal value, the straw elasticity is enhanced, the bonding effect is weakened and the relaxation density of the particles is reduced [34,35]. Reportedly, as the moisture content of straws rises, the relaxation ratio of crushed and fibrillated corn stover first declines and then increases, and it is very small when the moisture content is 15% [31] or 13.3% [32].
Compared with the 2 mm straws and under the same compression displacement, the volume relaxation ratio of the 4 mm straws was larger at a low moisture content but was smaller at a large moisture content. The reason was that the interaction between the water addition amount and the straw particle size significantly impacted the volume relaxation ratio of feed pellets. Small-particle-size straws have good filling, flowing and compression characteristics, tight interparticle bonding and small relaxation ratio [36]. At a high moisture content, the bonding between straws was weak. Compared to the 2 mm straws, the 4 mm straws had a larger contact area and a smaller rebound. For straws with the same particle size, the straw particles under compression displacement of 90 mm versus 92 mm had higher stability and smaller volume relaxation ratio under a low moisture content. However, at a large moisture content, the elasticity and resilience of straw particles were enhanced, and the relaxation ratio was larger.

3.1.2. Effect of Fermented Soybean Dregs on Volume Relaxation Ratio of Straw Formation

Analysis of variance was conducted with the experimental data of the volume relaxation ratio of feed pellets after fermented wet soybean dregs were added, and the results are shown in Table 2. The straw particle size and the added mass ratio of soybean dregs both have an extremely significant impact on the volume relaxation ratio of feed pellets, while compression displacement has no effect (Table 2). The interaction between the straw particle size and the added mass ratio of soybean dregs and the interaction between compression displacement and the added mass ratio of soybean dregs both have an extremely significant impact on the volume relaxation ratio of feed pellets. The interaction between straw particle size and compression displacement has no significant impact on the volume relaxation ratio of feed pellets. The effects of fermented soybean dregs on the volume relaxation ratio of feed formation are shown in Figure 3. With an increase in the added amount of fermented soybean dregs, the volume relaxation ratio decreased first and then increased, and the optimal amount was 5–10% (Figure 3). For the 2 mm straws, when the addition amounts of fermented soybean dregs were 5% and 10%, there was a significant difference in the volume relaxation ratio of feed molding compared to no addition, and the ratio decreased by 13.71–16.15% and 6.45–10%, respectively. For the 4 mm straws, when the amounts of fermented soybean dregs were 5% and 10%, there was a significant difference in the volume relaxation ratio of feed molding compared to no addition, and the ratio decreased by 7.59–8.82% and 9.56–12.41%, respectively. Compared with the 2 mm straws, under the same compression conditions, the 4 mm straws had larger volume relaxation ratio, which was different from the forming rules of pure straws, indicating the soybean dregs have a better bonding effect on small-particle straws under the large addition of soy dregs. The effect of compression displacement on the volume relaxation ratio of mixed feed formation was the same as that on straws. However, Guo et al. found that the relaxation ratio of mixed straw–potato residue materials decreased when the compression density increased [12]. The reason for the difference might be due to the different shape-maintaining time. In the above study [12], 900 s of shape maintaining could relax most of the residual stress in the formed material, so the particle size stability was always higher under larger compression density.
Comparison of Figure 2 and Figure 3 showed that, when water or wet fermented soybean dregs were added to the straws and the total moisture content of the feeds was the same, the volume relaxation ratio of the feed pellets added with fermented soybean dregs was lower than that of pellets added with water. This result indicated that the reason why adding fermented wet soybean dregs to straws improved the feed formation quality was that both the moisture it contained and the dregs played a positive role. Guo et al. found that adding wet potato residue to straws could also improve the molding quality [37]. Wet soybean dregs and wet potato residue both had high moisture contents, and with sufficient moisture, water-soluble carbohydrates in biomass could serve as binders [38]. Differently, potato residue contained a large amount of starch, and the lignin and starch in the mixture acted as binders when heated [37]. Moreover, soybean dregs contained a large amount of proteins and soluble dietary fibers composed of pectin, viscose and plant gum [39], which enhanced the adhesion between feed particles.

3.2. Maximum Compressive Force

3.2.1. Effects of Moisture on Maximum Compressive Force of Straws

Analysis of variance was conducted with the experimental data of the maximum compressive force of straws under water addition conditions, and the results are shown in Table 3. The straw particle size, compression displacement and water addition mass and their two-way interactions all had an extremely significant impact on the maximum compressive force (Table 3). Figure 4 shows the influence of moisture on the maximum compressive force of straws. For the 2 mm straws, the maximum compressive force decreased with the increase in straw moisture content at compression displacements of 90 and 92 mm (Figure 4). Compared with the untreated straws, when the amount of added water was 0.74 g (straw moisture content was 22.36%), there was a significant difference in the maximum compressive force, and it decreased by 45.44% and 43.41%, respectively. For the 4 mm straws, under the compression displacement of 90 mm, the maximum compressive force was weakened as the moisture content of straws increased. Compared with the untreated straws, when the amount of added water was 0.74 g (straw moisture content was 22.36%), there was a significant difference in the maximum compressive force, which decreased by 28.88%. When the compression displacement was 92 mm, the maximum compression force first decreased and then increased. When the amount of added water was 0.15 g (straw moisture content was 11.33%), the maximum compression force of straws was the smallest, and there was a significant difference compared to the straws without water; the maximum compression force was reduced by 21.12%. The reason for the above phenomenon was that, when the moisture content increased, the straws were softened, and the maximum compressive force was weakened. However, for the straws with a large particle size, when the moisture content and compression displacement were both large, the straw particles could not easily combine with each other, and the potential layer formed inside made the particles mutually repel [40], so the forming force was strengthened instead.
Under the same water addition amount and compression displacement, the maximum compressive force of the 4 mm straws is higher compared with the 2 mm straws, and there is a significant difference between the two samples in each group. The reason was that small-particle-size straws had stronger compression rheology and could fill in gaps, while large-particle-size straws had a large compression elastic deformation and a large forming force [41]. For straws of the same particle size and moisture content, when the compression displacement increased, the maximum compressive force was increased significantly. The reason for the above phenomenon was that the straws were loose in the early stage of compression, where the gaps between straws were eliminated first, so the straws contacted each other. In the later stage of compression, the straws were mainly close to each other or inlaid mutually, and the forming force was strengthened rapidly [14,42].

3.2.2. Effects of Fermented Soybean Dregs on Maximum Compressive Force of Straws

Analysis of variance was conducted with the experimental data of the maximum compressive force of feeds after the addition of fermented soybean dregs, and the results are shown in Table 4. The straw particle size, compression displacement, added mass ratio of soybean dregs and their two-way interactions all have an extremely significant impact on the maximum compressive force (Table 4). Figure 5 shows the influence of fermented soybean dregs’ addition on the maximum compressive force of feeds. With an increase in the added amount of fermented soybean dregs, the maximum compressive force decreased first and then increased (Figure 5). For the 4 mm straws, under the compression displacement of 90 mm, the maximum compressive force increased and then decreased. The reason may be that, as the amount of soybean dregs increased, the influence of moisture on the maximum compressive force surpassed the bonding effect of the soybean dregs. For the 4 mm straws, under the compression displacement of 92 mm, when the added mass ratio of soybean dregs increased from 10% to 25%, the maximum compressive force significantly increased. The reason was that the bulk density of the 4 mm straws was higher, and the increase in the added mass ratio of soybean dregs led to an increase in the feed mass in the mold. At this time, the feeding amount of feeds had a significant impact on the maximum compressive force. For the 2 mm straws, the appropriate addition amount of fermented soybean dregs was 5% or 10%. Compared with the untreated straws, the maximum compression force decreased by 9.03–10.81% and 19.37–21.23%, respectively. When the addition amount of fermented soybean dregs was 5%, there was a significant difference between the two groups, while when the addition amount was 10%, there was no significant difference between the two groups. The optimal addition amount of fermented soybean dregs for the 4 mm straws was 5%. Compared with the untreated straws, the maximum compression force decreased by 7.39–8.55%, but there was no significant difference.
When the added amount of soybean dregs and the particle size of straws were the same, there was a significant difference in the maximum compressive force at the compression displacements of 90 mm and 92 mm. When the added amount of soybean dregs and the compression displacement were the same, there was a significant difference in the maximum forming force between the 2 mm and 4 mm straws. The main component of the mixed feeds is straws, which is similar to the phenomenon after the addition of water to the straws. The reason has been explained earlier.
Comparison of Figure 4 and Figure 5 showed that, when the addition amount of water was the same, the maximum compressive force of the feeds added with fermented soybean dregs was greater than that with direct addition of water. It was indicated that suitable moisture could soften the straws and was conducive to the compression rheology of the straws, thus reducing the maximum compressive force. The soybean dregs had a bonding effect that hindered the compression rheology of the material, causing an increase in the maximum compressive force.

3.3. Specific Energy Consumption of Forming

3.3.1. Effect of Moisture on Specific Energy Consumption of Straw Forming

The research results indicate that the specific energy consumption of straw formation is mainly compressive specific energy consumption, accounting for 94.86–98.71% of the total energy consumption. Therefore, this study mainly analyzed the compressive specific energy consumption. The variance analysis of the experimental data on the compressive energy consumption of straws under water addition conditions is shown in Table 5. The straw particle size, compression displacement and water addition mass all had an extremely significant impact on the compressive specific energy consumption (Table 5). In the interaction, all two-way interactions had an extremely significant impact on the compressive specific energy consumption. The effect of moisture on the compressive energy consumption of straw molding is shown in Figure 6. With the increase in water addition mass, the compressive specific energy consumption decreased (Figure 6). For the 2 and 4 mm straws, when the compression displacements were 90 and 92 mm and the water addition was 0.74 g (straw moisture content was 22.36%), there was a significant difference in compressive specific energy consumption compared to that of straws without water, with a reduction of 23.87–42.23%. Wang et al. found that, when the moisture content of corn stover increased from 8% to 24%, the specific energy consumption for compression dropped by 8–46% [17], which was the same conclusion as our study. The reason was that, with the increase in moisture content, water can form a liquid bridge, and the liquid film could act as a lubricant. During the formation, the friction between straws and the friction between straws and the mold could be reduced, so the compression energy consumption of straws and the extrusion energy consumption of formed pellets decreased [43,44]. Li et al. showed that, when the moisture content rose from 5–20%, the energy consumption of formation decreased [45]. When the moisture content was 25%, the added water caused the extrusion of carbohydrates and proteins, which increased the viscosity between the particles and the inner surface of the mold and reduced the relative movement between the materials, thus increasing specific energy consumption.
With all other conditions unchanged, the 4 mm straws compared with the 2 mm straws consumed more compressive specific energy, and there was a significant difference between the two samples in each group, because the low bulk density and poor compression rheological properties of large-particle-size straws resulted in a high compressive force. The compressive specific energy consumption was significantly greater when the compression displacement was 92 mm versus 90 mm. The reason was that the forming force in the later stage of compression was enhanced rapidly, so the compressive energy consumption was significantly greater. Cui et al. found that, when the maximum compressive force increased from 80 to 120 MPa, the compressive energy consumption of the materials rose by 43.9% [33].

3.3.2. Effects of Fermented Soybean Dregs on Specific Energy Consumption of Straw Formation

The research results indicate that the specific energy consumption of the straw and soybean dregs mixed feed molding is mainly compressive specific energy consumption, accounting for 94.84–98.71% of the total energy consumption. Therefore, this study mainly analyzed the compressive specific energy consumption. Variance analysis was conducted on the experimental data of the compressive specific energy consumption of feeds under the addition of fermented soybean dregs, and the results are shown in Table 6. The straw particle size, compression displacement, added mass ratio of soybean dregs and their two-way interactions all had an extremely significant impact on the compressive specific energy consumption (Table 6). The effect of the addition amount of fermented soybean dregs on the compressive specific energy consumption of feed formation is shown in Figure 7. With an increase in the added amount of fermented soybean dregs, the compressive specific energy consumption decreased first and then increased (Figure 7). For the 4 mm straws, under the compression displacement of 90 mm, the compressive specific energy consumption decreased again, which owed to the decline of forming force. When the amounts of fermented soybean dregs were 5% and 10%, the compressive specific energy consumption of mixed feed formation was low. For the 2 mm straws, there were significant differences in compression energy consumption compared to the untreated straws, with reductions of 6.89–15.61% and 16.29–22.35%, respectively. For the 4 mm straws, although the compression specific energy consumption decreased by 5.67–13.40% and 6.35–8.51%, respectively, there was no significant difference between them when the compression displacement was 90 mm.
When the added amount of soybean dregs and the particle size of straws were the same, there was a significant difference in the compression energy consumption at compression displacements of 90 mm and 92 mm. When the added amount of soybean dregs and the compression displacement were the same, there was a significant difference in the compression energy consumption between the 2 mm and 4 mm straws. The main component of mixed feeds was straws, which was similar to the phenomenon under the condition of adding water to straws. The reason has been explained earlier.
Comparison of Figure 6 and Figure 7 showed that, when the addition amount of water was the same, the straw compressive energy consumption of the feeds added with fermented soybean dregs was greater than that under direct addition of water. The reason was that the soybean dregs were viscous, which was not conducive to the compression rheology of straws.
For the 2 mm corn stover, when the compression displacements were 90 mm and 92 mm and the added amount of fermented soybean dregs was 10%, the volume relaxation of the pellets was relatively small and the maximum molding force and compressive energy consumption were also small. For the 4 mm straws, when the compression displacements were 90 and 92 mm and the added amount of fermented soybean dregs was 5%, the volume relaxation of the pellets was relatively small and the maximum molding force and compressive energy consumption were also small. However, for straw grinding, the screen size had a significant impact on energy consumption. Naimi L.J. et al. found that, when using a hammer mill to grind corn stover (with a moisture content of 10%), the average energy input was approximately 18 kWh/t with a 6.4 mm screen mesh. When a 3.2 mm screen mesh was used, the average energy input was nearly twice that of the 6.4 mm screen mesh [46]. Another study observed that total specific energy for size reduction of wheat straws using a 1.6 mm hammer mill screen size was twice that for a 3.2 mm screen [47]. Meanwhile, a smaller grinding particle size of straws led to a lower grinding rate. In addition, when the addition mass ratio of fermented wet soybean dregs was greater than 10%, the moisture content of feed pellets processed from straws and fermented wet soybean dregs was greater than 13%. There was a risk of mold growth when stored directly after processing, so the feeds should be dried before storage. However, the drying process requires significant amounts of energy and time, leading to a significant increase in the cost of feed processing and a decrease in efficiency. Therefore, a mass ratio of 4 mm straw particles and 5% wet soybean dregs was recommended for pelleting. When extruding a mixture of 4 mm straw particles with 5% wet fermented soybean dregs, reducing compression displacement from 92 mm to 90 mm lowered the maximum forming force and energy consumption. However, this condition caused a greater volume relaxation and a higher pulverization rate. Therefore, it was recommended to use a mass ratio of 4 mm straw particles and 5% wet soybean dregs for granulation. When extruding a mixture of 4 mm straw particles and 5% wet fermented soybean dregs, reducing the compression displacement from 92 mm to 90 mm can reduce the maximum molding force and energy consumption. However, this condition could lead to a larger volume relaxation of particles, making them prone to breakage and leading to a high pulverization rate. Therefore, a compression displacement of 92 mm was recommended for pelleting. Based on the above analysis, the optimal pelleting process for mixed feeds of corn stover and wet fermented soybean dregs is as follows: a straw particle size of 4 mm, an added mass ratio of wet fermented soybean dregs of 5% and a compression displacement of 92 mm. Under these process conditions compared with the untreated straws, both the volume relaxation ratio and compressive energy consumption are significantly smaller, while the maximum forming force is smaller, but the difference is not significant. In addition, feed pellets produced from straws and wet soybean dregs do not require drying and have low production costs.

4. Conclusions

Under certain conditions, adding water or wet fermented soybean dregs to straws is beneficial for pelleting. Adding wet fermented soybean dregs to straws can improve the nutritional value of feeds and promote the utilization of agricultural wastes. Therefore, adding wet fermented soybean dregs is an effective method for processing high-quality feed pellets. When wet fermented soybean dregs are added at an appropriate amount, both the moisture content and the dregs improve the volume relaxation of formed pellets, and the moisture also reduces maximum compressive force and energy consumption.
Under the condition of adding wet fermented soybean dregs, except for compression displacement, which had no significant effect on the volume relaxation ratio of feed pellets, other factors had a significant impact on the indicators. Taking into account the quality and specific energy consumption of mixed feed processing, the optimal pelleting process for corn stover and wet fermented soybean dregs mixed feeds is as follows: a straw particle size of 4 mm, an added mass ratio of wet fermented soybean dregs of 5% and a compression displacement of 92 mm. Under these process conditions, compared with the untreated straws, both the volume relaxation ratio and compressive energy consumption are significantly smaller, while the maximum forming force is smaller, but the difference is not significant.
The results can provide a basis for scholars to study the pelleting process and equipment of straw and wet soybean dregs and also provide a reference for farmers to process feed pellets. In the future, it is necessary to explore the pelleting process by mixing high-moisture agricultural wastes (e.g., distiller’s grains and tail vegetables) with low-moisture wastes such as straw and threshed sunflower heads. This approach aims to solve agricultural waste disposal issues while promoting the development of animal husbandry.

Author Contributions

Conceptualization, T.C. and Y.S.; methodology, T.C.; software, W.Z.; validation, T.C., W.Z. and Y.S.; formal analysis, W.Z.; investigation, T.C.; resources, Y.S.; data curation, W.Z.; writing—original draft preparation, W.Z.; writing—review and editing, T.C. and Y.W.; visualization, W.Z.; supervision, Y.S.; funding acquisition, T.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China Youth Fund (No. 52305271).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The feed densification testing system.
Figure 1. The feed densification testing system.
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Figure 2. Effect of water addition mass on volume relaxation ratio. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average volume relaxation ratio of feed pellets with different water addition masses, as indicated by different lowercase letters. The symbols * and ns above the short horizontal line indicate that there is a significant difference (p < 0.05) and no significant difference (p > 0.05), respectively, in the average volume relaxation ratio of feed pellets under different compression displacements for the same water addition mass and straw particle size. The symbols ** and ns above the long horizontal line indicate that there is a significant difference (p < 0.05) and no significant difference (p > 0.05), respectively, in the average volume relaxation ratio of feed pellets under different straw particle sizes with the same added mass of water and compression displacement.
Figure 2. Effect of water addition mass on volume relaxation ratio. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average volume relaxation ratio of feed pellets with different water addition masses, as indicated by different lowercase letters. The symbols * and ns above the short horizontal line indicate that there is a significant difference (p < 0.05) and no significant difference (p > 0.05), respectively, in the average volume relaxation ratio of feed pellets under different compression displacements for the same water addition mass and straw particle size. The symbols ** and ns above the long horizontal line indicate that there is a significant difference (p < 0.05) and no significant difference (p > 0.05), respectively, in the average volume relaxation ratio of feed pellets under different straw particle sizes with the same added mass of water and compression displacement.
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Figure 3. Effect of added mass ratio of fermented soybean dregs on volume relaxation ratio. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average volume relaxation ratio of feed pellets with different added mass ratios of fermented soybean dregs, as indicated by different lowercase letters. The symbols * and ns above the short horizontal line indicate that there is a significant difference (p < 0.05) and no significant difference (p > 0.05), respectively, in the average volume relaxation ratio of feed pellets under different compression displacements for the same added mass ratio of fermented soybean dregs and the same straw particle size. The symbols ** and ns above the long horizontal line indicate that there is a significant difference (p < 0.05) and no significant difference (p > 0.05), respectively, in the average volume relaxation ratio of feed pellets under different straw particle sizes with the same added mass ratio of fermented soybean dregs and the same compression displacement.
Figure 3. Effect of added mass ratio of fermented soybean dregs on volume relaxation ratio. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average volume relaxation ratio of feed pellets with different added mass ratios of fermented soybean dregs, as indicated by different lowercase letters. The symbols * and ns above the short horizontal line indicate that there is a significant difference (p < 0.05) and no significant difference (p > 0.05), respectively, in the average volume relaxation ratio of feed pellets under different compression displacements for the same added mass ratio of fermented soybean dregs and the same straw particle size. The symbols ** and ns above the long horizontal line indicate that there is a significant difference (p < 0.05) and no significant difference (p > 0.05), respectively, in the average volume relaxation ratio of feed pellets under different straw particle sizes with the same added mass ratio of fermented soybean dregs and the same compression displacement.
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Figure 4. Effect of water addition mass on maximum compressive force of straws. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average maximum compressive force of feeds with different water addition masses, as indicated by different lowercase letters. The symbol * above the short horizontal line indicates that there is a significant difference (p < 0.05) in the average maximum compressive force of feeds under different compression displacements for the same water addition mass and straw particle size. The symbol ** above the long horizontal line indicates that there is a significant difference (p < 0.05) in the average maximum compressive force of feed under different straw particle sizes with the same added mass of water and compression displacement.
Figure 4. Effect of water addition mass on maximum compressive force of straws. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average maximum compressive force of feeds with different water addition masses, as indicated by different lowercase letters. The symbol * above the short horizontal line indicates that there is a significant difference (p < 0.05) in the average maximum compressive force of feeds under different compression displacements for the same water addition mass and straw particle size. The symbol ** above the long horizontal line indicates that there is a significant difference (p < 0.05) in the average maximum compressive force of feed under different straw particle sizes with the same added mass of water and compression displacement.
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Figure 5. Effect of added mass ratio of fermented soybean dregs on maximum compressive force of straws. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average maximum compressive force of feeds with different added mass ratios of fermented soybean dregs, as indicated by different lowercase letters. The symbol * above the short horizontal line indicates that there is a significant difference (p < 0.05) in the average maximum compressive force of feeds under different compression displacements for the same added mass ratio of fermented soybean dregs and the same straw particle size. The symbol ** above the long horizontal line indicates that there is a significant difference (p < 0.05) in the average maximum compressive force of feeds under different straw particle sizes with the same added mass ratio of fermented soybean dregs and the same compression displacement.
Figure 5. Effect of added mass ratio of fermented soybean dregs on maximum compressive force of straws. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average maximum compressive force of feeds with different added mass ratios of fermented soybean dregs, as indicated by different lowercase letters. The symbol * above the short horizontal line indicates that there is a significant difference (p < 0.05) in the average maximum compressive force of feeds under different compression displacements for the same added mass ratio of fermented soybean dregs and the same straw particle size. The symbol ** above the long horizontal line indicates that there is a significant difference (p < 0.05) in the average maximum compressive force of feeds under different straw particle sizes with the same added mass ratio of fermented soybean dregs and the same compression displacement.
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Figure 6. Effect of moisture on compressive specific energy consumption of straw densification. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average compressive specific energy consumption of feeds with different water addition masses, as indicated by different lowercase letters. The symbol * above the short horizontal line indicates that there is a significant difference (p < 0.05) in the average compressive specific energy consumption of feeds under different compression displacements for the same water addition mass and straw particle size. The symbol ** above the long horizontal line indicates that there is a significant difference (p < 0.05) in the average compressive specific energy consumption of feeds under different straw particle sizes with the same added mass of water and compression displacement.
Figure 6. Effect of moisture on compressive specific energy consumption of straw densification. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average compressive specific energy consumption of feeds with different water addition masses, as indicated by different lowercase letters. The symbol * above the short horizontal line indicates that there is a significant difference (p < 0.05) in the average compressive specific energy consumption of feeds under different compression displacements for the same water addition mass and straw particle size. The symbol ** above the long horizontal line indicates that there is a significant difference (p < 0.05) in the average compressive specific energy consumption of feeds under different straw particle sizes with the same added mass of water and compression displacement.
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Figure 7. Effect of added mass ratio of fermented soybean dregs on compressive specific energy consumption of feed densification. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average compressive specific energy consumption of feeds with different added mass ratios of fermented soybean dregs, as indicated by different lowercase letters. The symbol * above the short horizontal line indicates that there is a significant difference (p < 0.05) in the average compressive specific energy consumption of feeds under different compression displacements for the same added mass ratio of fermented soybean dregs and straw particle size. The symbol ** above the long horizontal line indicates that there is a significant difference (p < 0.05) in the average compressive specific energy consumption of feed under different straw particle sizes with the same added mass ratio of fermented soybean dregs and compression displacement.
Figure 7. Effect of added mass ratio of fermented soybean dregs on compressive specific energy consumption of feed densification. T11 and T12 represent the 2 mm corn stover with compression displacements of 90 and 92 mm, respectively; T21 and T22 represent the 4 mm corn stover with compression displacements of 90 and 92 mm, respectively. Under the same straw particle size and compression displacement, a significant difference (p < 0.05) was observed in the average compressive specific energy consumption of feeds with different added mass ratios of fermented soybean dregs, as indicated by different lowercase letters. The symbol * above the short horizontal line indicates that there is a significant difference (p < 0.05) in the average compressive specific energy consumption of feeds under different compression displacements for the same added mass ratio of fermented soybean dregs and straw particle size. The symbol ** above the long horizontal line indicates that there is a significant difference (p < 0.05) in the average compressive specific energy consumption of feed under different straw particle sizes with the same added mass ratio of fermented soybean dregs and compression displacement.
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Table 1. Variance analysis of the volume relaxation ratio for feed pellets under water addition.
Table 1. Variance analysis of the volume relaxation ratio for feed pellets under water addition.
Source of VarianceFreedomMean SquareFSignificance
Corrected model230.28 55.76 0.000 **
Intercept1307.41 60,529.97 0.000 **
Straw particle size10.22 44.20 0.000 **
Compression displacement10.04 7.43 0.007 **
Water addition mass51.02 201.29 0.000 **
Straw particle size × Compression displacement10.03 6.50 0.012 *
Straw particle size × Water addition mass50.19 36.61 0.000 **
Compression displacement × Water addition mass50.02 4.36 0.001 **
Error1200.01
Total144
Revised total143
Note: R2 = 0.914, adjusted R2 = 0.898. ** indicates extremely significant (p < 0.01); * indicates significant (p < 0.05).
Table 2. Variance analysis of the volume relaxation ratio for feed pellets under soybean dregs addition.
Table 2. Variance analysis of the volume relaxation ratio for feed pellets under soybean dregs addition.
Source of VarianceFreedomMean SquareFSignificance
Corrected model230.22 90.54 0.000 **
Intercept1270.80 110,826.720.000 **
Straw particle size10.31 125.21 0.000 **
Compression displacement10.01 3.21 0.076 ns
Added mass ratio of soybean dregs50.90 368.31 0.000 **
Straw particle size × Compression displacement10.00 1.51 0.221 ns
Straw particle size × Added mass ratio of soybean dregs50.03 12.99 0.000 **
Compression displacement × Added mass ratio of soybean dregs50.02 6.18 0.000 **
Error1200.00
Total144
Revised total143
Note: R2 = 0.946, adjusted R2 = 0.935. ** indicates extremely significant (p < 0.01); ns indicates insignificance (p > 0.05).
Table 3. Variance analysis of maximum compressive force for feed under water addition.
Table 3. Variance analysis of maximum compressive force for feed under water addition.
Source of VarianceFreedomMean SquareFSignificance
Corrected model23214,380,049.43 274.68 0.000 **
Intercept114,018,402,133.78 17,961.35 0.000 **
Straw particle size12,575,071,940.03 3299.36 0.000 **
Compression displacement11,659,761,180.03 2126.60 0.000 **
Water addition mass522,017,396.11 28.21 0.000 **
Straw particle size × Compression displacement1353,039,047.11 452.34 0.000 **
Straw particle size × Water addition mass517,474,044.59 22.39 0.000 **
Compression displacement × Water addition mass512,402,128.39 15.89 0.000 **
Error120780,475.79
Total144
Revised total143
Note: R2 = 0.981, adjusted R2 = 0.978. ** indicates extremely significant (p < 0.01).
Table 4. Variance analysis of maximum compressive force for feed under soybean dregs’ addition.
Table 4. Variance analysis of maximum compressive force for feed under soybean dregs’ addition.
Source of VarianceFreedomMean SquareFSignificance
Corrected model23671,810,222.82175.560.000 **
Intercept126,402,756,365.566899.660.000 **
Straw particle size15,835,139,275.341524.860.000 **
Compression displacement14,773,646,887.511247.470.000 **
Added mass ratio of soybean dregs5211,786,065.5855.340.000 **
Straw particle size × Compression displacement11,460,163,312.67381.570.000 **
Straw particle size × Added mass ratio of soybean dregs5121,724,789.8231.810.000 **
Compression displacement × Added mass ratio of soybean dregs5212,979,577.4255.660.000 **
Error1203,826,676.34
Total144
Revised total143
Note: R2 = 0.971, adjusted R2 = 0.966. ** indicates extremely significant (p < 0.01).
Table 5. Variance analysis of compressive specific energy consumption for feed under water addition.
Table 5. Variance analysis of compressive specific energy consumption for feed under water addition.
Source of VarianceFreedomMean SquareFSignificance
Corrected model23483.70 372.23 0.000 **
Intercept137,844.84 29,123.90 0.000 **
Straw particle size18651.02 6657.48 0.000 **
Compression displacement11743.69 1341.87 0.000 **
Water addition mass596.30 74.11 0.000 **
Straw particle size × Compression displacement1176.56 135.87 0.000 **
Straw particle size × Water addition mass55.71 4.39 0.001 **
Compression displacement × Water addition mass56.77 5.21 0.000 **
Error1201.30
Total144
Revised total143
Note: R2 = 0.986, adjusted R2 = 0.984. ** indicates extremely significant (p < 0.01).
Table 6. Variance analysis of compressive specific energy consumption for feed under soybean dregs’ addition.
Table 6. Variance analysis of compressive specific energy consumption for feed under soybean dregs’ addition.
Source of VarianceFreedomMean SquareFSignificance
Corrected model23 633.32 272.13 0.000 **
Intercept1 48,177.69 20,701.11 0.000 **
Straw particle size1 10,396.35 4467.13 0.000 **
Compression displacement1 2915.55 1252.76 0.000 **
Added mass ratio of soybean dregs5 35.58 15.29 0.000 **
Straw particle size × Compression displacement1 602.91 259.06 0.000 **
Straw particle size × Added mass ratio of soybean dregs5 15.09 6.48 0.000 **
Compression displacement × Added mass ratio of soybean dregs5 45.67 19.62 0.000 **
Error120 2.33
Total144
Revised total143
Note: R2 = 0.981, adjusted R2 = 0.978. ** indicates extremely significant (p < 0.01).
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MDPI and ACS Style

Chen, T.; Zhang, W.; Song, Y.; Wang, Y. Effects of Wet Soybean Dregs on Forming Relaxation Ratio, Maximum Compressive Force and Specific Energy Consumption of Corn Stover Pellets. Agriculture 2025, 15, 1727. https://doi.org/10.3390/agriculture15161727

AMA Style

Chen T, Zhang W, Song Y, Wang Y. Effects of Wet Soybean Dregs on Forming Relaxation Ratio, Maximum Compressive Force and Specific Energy Consumption of Corn Stover Pellets. Agriculture. 2025; 15(16):1727. https://doi.org/10.3390/agriculture15161727

Chicago/Turabian Style

Chen, Tianyou, Wenyu Zhang, Yuqiu Song, and Yanlin Wang. 2025. "Effects of Wet Soybean Dregs on Forming Relaxation Ratio, Maximum Compressive Force and Specific Energy Consumption of Corn Stover Pellets" Agriculture 15, no. 16: 1727. https://doi.org/10.3390/agriculture15161727

APA Style

Chen, T., Zhang, W., Song, Y., & Wang, Y. (2025). Effects of Wet Soybean Dregs on Forming Relaxation Ratio, Maximum Compressive Force and Specific Energy Consumption of Corn Stover Pellets. Agriculture, 15(16), 1727. https://doi.org/10.3390/agriculture15161727

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