1. Introduction
Potato is a tuber crop that contains all the essential nutrients required for maintaining proper health [1]. It is one of the most vital vegetable crops cultivated in Saudi Arabia and the world [2]. The processes of land preparation, planting, cultivation, harvesting, and post-harvest practices are mechanized, which has a detrimental effect on potato production [3]. In fact, every progress in mechanization impacts the quantity and quality of potato production [4]. The quality of potato tubers is carefully related to the structural and chemical features of the plant materials. It differs depending on diverse influences, such as climate, agricultural practices, cultivars, maturity at the time of harvesting, and method of harvesting [5]. However, other agricultural practices, like fertilization parameters, can influence the mechanical resistance of the fruit [6,7].
Potato is becoming an increasingly important crop as it is a staple nutrition in most nations and is an excellent and cheap source of calories [8,9]. The planting depth is the main factor affecting potato yield and tuber quality [10]. The planting depth for most soil types in Saudi Arabia is recommended to be 10 to 15 cm [11]. The purpose of tillage in potato cultivation is to control weeds, facilitate planting, and increase the ease of future cultivation and harvest [12,13,14,15]. No typical tillage tool is used in the seedbed preparation of the fields of cultivated potatoes. Still, having as few procedures as possible is preferred to save time and fuel and decrease extreme soil compaction [16]. The most common tillage procedure is to plow the former year’s crop residue with a moldboard plow in a specified time. A disk harrow can be used to break large soil clods if they exist; this is normally followed by the leveling or smoothening of the soil using a spring-tooth harrow to incorporate fertilizer [17]. Three tillage systems for potato production can be considered: minimum tillage (15–18 cm deep), conventional tillage (22–25 cm deep), and deep tillage (33–35 cm deep), as reported by Saue et al. [18].
During harvesting, transport, storage, and packing, fruits and vegetables are subjected to physical damage, which directly affects their quality and, consequently, results in a loss in their commercial value [19]. Traditionally, most of the techniques for the evaluation of the mechanical behavior of fruits or vegetables have been focused on obtaining information from a single fruit, and the average value of several measurements taken from the fruit was considered representative of its behavior. However, fruits and vegetables are not homogenous in structure but are a complex conglomerate of tissues that consist of cells. The mechanical properties of agricultural products play a major role in processing, handling, harvesting, trading, quality control, and creating new products. Moreover, these characteristics are the most critical constraints that reflect the quality of the agricultural produce [20,21].
It is necessary to mount the quality-connected features to investigate and control quality. The quality of produce is determined by its sensory attributes, nutritive values, chemical constituents, mechanical and functional characteristics, defects [22], and mechanical properties related to the texture of the produce [22]. Potatoes are primarily harvested mechanically on commercial plantations, although there is a growing demand for potatoes that meet the quality standards set by the food and pharmaceutical industries. Therefore, it is essential to look into the mechanical characteristics as this will allow for the determination of the best times for harvest and storage and to support the development and design of a definite machine and its action [23]. Moreover, food’s mechanical, morphological, and physical properties are important in the aeration and separation procedures [24]. The mechanical properties of potato tubers are essential for building numerous farm machinery components [25].
It will be feasible to improve the product’s quality and raise its economic value with the knowledge gathered by studying how fruits react to outside influences [26]. The cellular underpinnings of fruit texture and the aspects of human physiology related to its perception were examined by Harker et al. [27]. The well-known puncture, compression, and shear tests, as well as creep, impact, and sonic and ultrasonic testing, are examples of mechanical tests for texture; these tests were reviewed by Brown and Jr. Sarig [28], Chen [29], and Abbott et al. [30]. Fruits and vegetables show viscoelastic behavior under mechanical loading, which depends on both the force and the loading rate. However, they are frequently believed to be elastic for practical purposes, and the loading rate is typically disregarded. While viscoelastic measurement considers the functions of force, deformation, and time, measuring elastic characteristics considers force and deformation. Modulus of elasticity, a bioyield point, a rupture point, and hardness as mechanical properties for fruits and vegetables are usually extracted from the force–deformation curves obtained from compression tests, as described in [22,31,32,33]. However, the force–deformation curve of agricultural produce with a demonstration of a bioyield point is discussed in [34].
In its unprocessed state, biological material such as potato tubers is handled and processed mechanically. As a result, information about the mechanical characteristics of potato tubers after harvest is crucial for the development and implementation of different handling, packaging, storing, and transportation methods [35]. The majority of mechanical attributes documented in the literature were examined using individual samples and mechanical testing, including tensile, compression, penetration, cutting, tearing, puncturing, and shearing tests [36,37].
The mechanical characteristics of the potato tubers of the “Kufri Badshah” variety were ascertained by Patel et al. [36]. The test was conducted using an Instron universal testing machine (Model 1000, Instron) to determine the rupture force under compression. A quasi-static compression test was conducted using the Instron universal testing machine, which is outfitted with a 5000 N compression load cell, an integrator, and a chart recorder. The crosshead was adjusted to move at a steady 20 mm/min. For fresh potato tubers, the force–deformation curve of five samples was acquired, and the average value of the five measurements was published.
According to Solomon and Jindal’s [38] research, the elasticity modulus corresponding to 2.5%, 5%, and 7.5% compression was obtained because of the nonlinearity of the force–deformation data of the potato tissue. Nevertheless, they used potatoes (cv. spunta) that were just harvested and bought two days after harvesting in northern Thailand. They said that the fresh potato tangent modulus of elasticity values were 2.64, 2.69, and 2.75 MPa, respectively, equivalent to 2.5%, 5%, and 7.5% compression. The fresh potatoes showed a connection that resembled a straight line, which is typical of elastic materials. Moreover, Golmohammadi [37] reported that the mean, maximum, and minimum values of the elasticity modulus of potatoes at 0.02 strains were 2.523 MPa, 2.993 MPa, and 2.115 MPa, respectively.
Ahangarnezhad et al. [39] reported using the uniaxial compression test in conjunction with a universal testing instrument (MRT-5 SANTAM Company, Germany) to ascertain the mechanical properties of the potato samples. Drawing the force–deformation diagram of the safe samples between two parallel plates was the aim of this test. A loading speed of 20 mm/min was used. Additionally, cylindrical samples with a 14 mm diameter and 28 mm height were made by flattening the top and bottom of the samples with a thin blade in order to measure the modulus of elasticity. They stated that the potato elasticity modulus had mean, maximum, minimum, and standard deviation values of 3.09, 3.70, 2.66, and 0.43 MPa, respectively.
Lammari et al. [24] ran tensile and compression tests on two varieties of potato tubers—spunta and daifla—to determine the mechanical behavior of the two varieties. The modulus of elasticity can be calculated using the deformation obtained from tensile tests. Potato tuber test pieces of 20 × 25 mm were utilized as cylindrical specimens for the compression test. The two types’ respective elasticity moduli were measured at 4 and 4.5 MPa. The application of coefficient of elasticity—the ratio of compressive force to deformation—as a gauge of fruit firmness was investigated by Fekete and Sass [40]. The coefficient of elasticity, bioyield, rupture stress, and Young’s modulus of elasticity were found to be positively correlated with each other.
Stress–strain tests are another way to extract the basic mechanical properties of agricultural produce. Jindal and Techasena [41] and Pang and Scanlon [42] reported that the modulus of elasticity of potatoes ranges from 2.7 to 2.9 MPa at 3% to 9% strain during axial compression. Solomon and Jindal [43] studied the effects of sample size, loading rate, and compression level on the determination of the modulus of elasticity of potatoes in axial and radial compression tests. The results revealed that the determination of the modulus of elasticity of potatoes during axial compression testing was significantly influenced by the testing conditions and sample size, whereas that during radial compression testing appeared to be independent of the testing conditions and sample size. However, the mechanical properties of agricultural produce play a vital part in their quality control processes and in the improvement of harvesting and handling farm implements to reduce economic losses [37]. Therefore, the current research aims to analyze the force–deformation curves of potatoes cv. Spunta to investigate the effects of three tillage implements used in Saudi Arabia for its seedbed preparation on its selected mechanical properties. The results attained can be a beneficial tool for the development of potatoes cv. spunta transporting, harvesting, and processing methods. The attained results were assessed using statistical analysis and force–deformation curve analysis.
2. Materials and Methods
2.1. Experimental Site
The study was performed on a private farm in Al-Kharj district, Saudi Arabia, during two growing seasons (the first season was 2014 and the second season was 2015). The soil and irrigation water samples were analyzed using standard methods in an accredited laboratory (IDAC, Riyadh, Saudi Arabia). The soil parameters such as sand, silt, clay percentages, organic matter percentage, pH, electrical conductivity, Na+, K+, Ca++, and Mg++ concentrations, soil moisture content, and soil bulk density were determined. The soil texture of the experimental field was classified by laboratory analysis according to standard methods as loamy sand (4.02% clay, 13.08% silt, and 82.9% sand). The experimental field’s average soil moisture content, bulk density, and cone index were 8.24% dry base, 1.58 g/cm3, and 2.19 MPa, respectively, at a soil depth of 0–15 cm. Table 1 shows the soil and water characteristics used in this research.
2.2. Experimental Design
Tillage operations with three different systems were performed, and the experimental design was a completely randomized block design with three replications. The tillage systems used for the tillage treatments were a moldboard plow (MBP), a disc harrow plow (DH), and a chisel plow (CHP). All the plows operated at a single tractor forward speed of 5.4 km/h. The specific tractor forward speed was achieved by selecting the appropriate gear. The adjusted tillage depth was 15 cm. The plot size was 12 m × 40 m, two meters apart. The tillage implements were pulled by a 78 kW tractor during the experiments, and the tillage treatments were evaluated in one pass. The mounted moldboard plow had two bodies and a working width of 80 cm. The chisel plow (mounted type) had fifteen shanks mounted in a staggered arrangement on two toolbars (eight shanks on a forward bar and seven shanks on a rearward bar). The chisel tool was 5 cm wide, and the chisel plow had a shank space of 45 cm; thus, the working width was 337.5 cm. The disc harrow (pull type) had 24 discs (56 cm in diameter) mounted on two gangs (12 discs in the forward and 12 discs in the rearward direction); thus, the working width was 280 cm. The soil preparation, fertilization, planting, and yield were performed as specified by Al-Hamed et al. [44].
2.3. Selecting the Fresh Potato Sample
Samples of the fresh potato variety “Spunta”, which was planted under different tillage methods, were gathered after harvesting the crop by a machine. The fresh potato samples were carefully packed by hand in paper pages; then, the fresh samples were transported to the Food Engineering Laboratory located at the Department of Agricultural Engineering, College of Food and Agriculture Sciences, King Saud University, Riyadh, Saudi Arabia. The fresh samples were stored at room temperature (about 23 °C). The fresh potato samples were cleaned from the soil and the damaged tubers were excluded manually. The required tests were run on the fresh samples. The potato tubers were classified by hand as one size as possible.
2.4. Force–Deformation Curve
This study investigated the force–deformation curves under compression, penetration, and shear tests of potatoes harvested using three tillage implements. A texture analyzer (TA-HDi, Model HD3128, Stable Micro Systems, Surrey, UK) was used to perform the tests. The texture analyzer was interfaced with a PC and Texture Expert Exceed software (version 2.05), which enables the textural data to be acquired and analyzed. All experiments were conducted at room temperature (23 °C). Before performing the tests, the load cell and probe distance of the instrument were calibrated using the methods and tools provided by the company. For the compression tests, the experiments were performed using individual potatoes oriented parallel to the compression surface at a crosshead speed of 1.5 mm/s to 15 mm distance using an aluminum plunger (P/75) with a 75 mm diameter. A probe (P/2) with a diameter of 2 mm was used in the penetration tests, whereas a craft knife was used in the shear tests. The penetration depth was 15 mm from the potato’s skin, with a probe speed of 1.5 mm/s. The craft knife was used to cut the potato into two longitudinal parts. Five individual potatoes harvested using each tillage implement were utilized for each test; however, the size of the samples was nearly the same. Different indicators were extracted from the force–deformation curves obtained from the compression tests [34]. The indicators included modulus of elasticity (N/mm), which is defined as the slope of a straight line as described by the force–deformation curve of agricultural produce [34], bioyield force (N), elastic range (mm), the rupture point (N), plastic range (mm), and hardness shown by the area under of the curve (N·mm). The maximum force and hardness were extracted from the force–deformation curves obtained from the penetration and shear tests. The different tests performed on the potatoes are depicted in Figure 1.
2.5. Statistical Analysis
The data analysis of the variance in this research work was generated using the SAS software version [9.2] of the SAS system [45]. The average of the five runs was reported as the measured value plus standard deviation. Duncan’s multiple range tests were used to evaluate significant differences between the mean values at a probability level of 5% (p < 0.05).
3. Results and Discussion
3.1. Analyzing Dimensions of the Potato Samples
Figure 2 shows the notations for the dimensions of the potato samples. The investigated potato samples after harvesting had mean lengths (L) of 106 ± 2 mm, 90 ± 3 mm, and 105 ± 2 mm, mean widths (W) of 62 ± 1 mm, 63 ± 2 mm, and 63 ± 1 mm, and thicknesses (T) of 50 ± 1 mm, 52 ± 1 mm, and 52 ± 2 mm for potatoes harvested with the disc harrow plow, chisel plow, and moldboard plow, respectively. Furthermore, the mean moisture contents (wet basis) were 82 ± 2%, 82 ± 1%, and 81 ± 2% for potatoes harvested with the disc harrow plow, chisel plow, and moldboard plow, respectively. In the study of Lammari et al. [24], for the Spunta tubers cultivar, the minimum mean length (L) of 59.39 mm and the maximum mean length (L) of 252.89 mm were noticed. Abdalgawad et al. [23] showed that the length (L) of potato tubers was 60.03 ± 3.48, 76.96 ± 4.05, and 89.93 ± 3.29 mm for small, medium, and large tubers, respectively. Potato tuber width (W) was 44.67 ± 2.71, 56.78 ± 2.19, and 60.02 ± 2.81 mm for small, medium, and large tubers, respectively. Also, potato tuber thickness (T) was 37.69 ± 1.99, 44.59 ± 2.31, and 44.64 ± 1.87 mm for small, medium, and large tuber size, respectively. It is clear that the dimensions data of the potato tubers are very significant in the storage capacity determination, packing, and handling.
3.2. Force–Deformation Curve Analysis
3.2.1. Compression Test
Even though the mechanical properties of agricultural produce appear straightforward, their outline and investigation are not simple tasks. The reason is that most fruits and vegetables are cellular materials [46]. Additionally, the potato tuber is a heterogeneous material, and the mechanical properties of the specimens varied considerably [47]. As an example, the experimentally measured force–deformation curves for five potatoes cv. Spunta in the disc harrow plow treatment are illustrated in Figure 3. However, different repetitions for each sample provided similar trends of force during the compression test at different deformation values. Furthermore, the shape of the curves obtained by the shear test when the force is plotted vs. the deformation is like those described in the previous research for other agricultural materials like banana fruit [48]. When agricultural products are subjected to compression forces, their strengths frequently behave differently. The compression forces generated during the product transfer must be lowered to the minimum rate (less than 194 N) in order to minimize mechanical damage [48]. Table 2 shows the significance probability for the mechanical property indicators under compression tests of potatoes cv. Spunta produced with different tillage implements.
The shapes of force–deformation curves presented in Figure 3 are typical of the compression seen in biological materials. Initially, the shape of the curve was linear, but a slight inflection was observed near the maxima in all the curves. This can be related to the first cracks [49] that appear on the samples as many researchers have confirmed a close connection between mechanical properties and the microstructure of biological materials [50,51,52]. The bioyield point depends on the mechanical resistance of the tissue, which is closely related to the potato cell size and cell wall thickness [53]. This finding agrees with that of Ávila et al. [46] who stated that the compressive bioyield point could be set as the maximum value that the curve could reach. The sudden decrease at this point indicates that the sample was fractured. As noted in Table 2, the only source of variation for all the indicators was the tillage implemented in the experiment. Table 3 also shows the mean values and standard deviations of all mechanical indicators extracted from the force–deformation curves. The modulus of elasticity of the potatoes cv. Spunta produced with the disc harrow plow was 5.88 N/mm and 5.89 N/mm for the first and second seasons, respectively. The equivalent values for potatoes produced with the chisel plow were 4.47 and 4.66 N/mm. The mean value for the moldboard plow treatment was 4.22 N/mm for both seasons. Overall, it is well known that understanding the mechanical characteristics of the potato cultivar Spunta is crucial for developing and improving systems associated with their cultivation, processing, and packing. The higher the modulus of elasticity is, the harder the potato tissue will be [48]. The overall average high modulus of elasticity of 4.89 N/mm (Table 3) in potatoes cv. Spunta shows higher resistance of the potatoes and their sensitivity to compression behavior; thus, potatoes cv. Spunta have a harder tissue. A higher modulus of elasticity causes smaller elastic strain that happens at a specified level of loading so that the material is stiffer or the structure of the material network is harder [54]. The harder tissue structure of the material shows that the water content of the material is low [54]. On the other hand, an object’s modulus of elasticity is independent of its size and shape and only depends on the kind of material it is made of [54]. Furthermore, the overall average bioyield force, elastic range, rupture point, plastic range, and hardness were 97.83 N, 3.00 mm, 118.75 N, 2.13 mm, 1671.52 N·mm, respectively, (Table 3) for fresh potatoes cv. Spunta.
In addition, as indicated in Table 3, the bioyield force was lower when potatoes were produced with the moldboard plow compared with other implements. The elastic ranges, which represent the recoverable deformation, i.e., the ability of the sample to return to its original shape when the forces are no longer applied, were significantly lower in the moldboard plow treatment than in other treatments. Similarly, the plastic ranges (the non-recoverable deformation), the rupture point (the maximum force that causes structural failure in the potato; N), and hardness (the force needed to produce the failure; N·mm) had the same trend. These changes may be related to the effects of the tillage operations on the soil [10]. Such differences may also be related to the moisture content of the samples [55] or the sizes of the potatoes [56].
3.2.2. Penetration Test
The penetration test, also called the puncture test, is often used to test the degree of ripeness of fruits and vegetables and the skin’s strength. This test measures the maximal penetration force by penetrating the flesh with a cylindrical probe to a predetermined depth [57]. Distinct curves are obtained depending on the skin and consistency of the potato tissue. Figure 4 shows the experimentally measured force–deformation curves obtained from the penetration tests for potatoes cv. Spunta produced using the disc harrow plow. However, different repetitions for each sample provided similar trends of force during the penetration test at different deformation values. Based on the penetration profiles (force vs. deformation) of potatoes produced with three tillage implements, as shown in the figures, it can be observed that the penetration curve can be approximated as a straight-line segment with one peak, which may be the rupture point at which a significant potato skin failure occurred. Its corresponding values can be used as the puncture strengths [58]. It can be observed in the figure that there are no sharp cracks seen in the curves, which implies that the potatoes had no crispness and crunchiness, as highly jagged curves imply a crispy or crunchy texture [59]. Crispness and crunchiness have traditionally been associated with the mechanical force required to compress the food until it fractures into small pieces [60]. However, the different repetitions for each sample provided similar trends of force during the penetration test at different deformation values. Furthermore, the information gained concerning the mechanical properties using the penetration test can be utilized in the factories that process potato products [48].
The significance probability for the maximum force and hardness in the penetration tests of potatoes cv. Spunta produced with different tillage implements in two seasons are presented in Table 4. The results show that only the type of tillage implemented significantly affected the penetration indicators. Figure 5 and Figure 6 illustrate the differences in measured values of the maximum force and hardness due to tillage treatment and the effect of planting season in the penetration tests. The maximum forces were 41.20 N, 44.86 N, and 47.16 N for potatoes produced in the first season with the disc harrow plow, chisel plow, and moldboard plow, respectively, whereas they were 41.44 N, 45.10 N, and 47.59 N, respectively, for the second season (Figure 5). The hardness values were 428.13 N·mm, 357.00 N·mm, and 315.30 N·mm for potatoes produced in the first season with the disc harrow plow, chisel plow, and moldboard plow, respectively, whereas they were 426.11 N·mm, 357.36 N·mm, and 315.49 N·mm for the second season (Figure 6). The hardness values for potatoes produced in the first and second seasons with the disc harrow were observed to be higher compared with other implements despite this implement having the maximum force. This behavior can be attributed to the soil as it has a clear effect on the mechanical properties of potatoes [61].
3.2.3. Shear Test
Shear testing measured the force needed to cut the potato specimen. The shear test also gives information about the toughness and tenderness of the potato. The measured quantitative values of shear force are technologically important in designing machines for mechanical harvesting and food processing plants [62]. Figure 7 depicts the experimentally measured force–deformation curves for Spunta cv. potatoes produced with the disc harrow plow, chisel plow, and moldboard plow, respectively. However, different repetitions for each sample provided similar trends of force during the shear test at different deformation values. The shape of the curves obtained by the shear test when the force is plotted vs. the deformation is like those described in the previous research for other agricultural materials, like melon, cantaloupe melon, honeydew melon, and watermelon [63].
Two indicators—maximum force and hardness—were extracted from the force–deformation curves obtained from the shear tests. As seen from Figure 7, the curves have a nonlinear shape. Each curve is composed of three sections. The first part is an approximately straight-line segment with a peak point of nearly 200 N; the second part is an approximately straight-line segment with a slope and peak point of nearly 400 N. The third part is a curve with unexpected peak points for potatoes produced with the disc harrow plow (Figure 7). This may be attributed to the fact that such samples were mature. The maturity stage clearly impacts the mechanical properties of vegetables [64]. Also, crop parameters and loading directions had an impact on the mechanical properties of small oil palm fruits [65], as well fruit structure and stress transfer mode may influence the mechanical parameters of fruits [66]. Unlike the shear test analysis, no significant differences were found in the maximum shear force and hardness of potatoes cv. Spunta produced with different tillage implements in two seasons. These data are summarized in Table 5. However, Table 6 illustrates the differences between tillage treatments as well as the effect of season on the maximum shear force and hardness obtained from the shear tests of potatoes cv. Spunta. The maximum shear forces were 750.36 N, 44.86 N, and 772.67 N for potatoes produced in the first season with disc harrow, chisel, and moldboard plows, respectively, whereas they were 706.36 N, 750.67 N, and 704.43 N for the second season. The hardness values for the first season were 21,428.12 N·mm, 19,747.17 N·mm, and 19,915.30 N·mm for potatoes produced with disc harrow, chisel, and moldboard plows, respectively, whereas they were 20,728.12 N·mm, 19,478.17 N·mm, and 19,495.30 N·mm, respectively, for the second season. These outcomes may be attributed to such samples resulting in high variation in the maximum shear force and hardness; based on those variables, no significant differences were observed. Nonetheless, the information obtained regarding the mechanical characteristics using the shear test can be utilized in the factories that process potatoes [48]. According to Jahanbakhshi [67], 33.66 N was the average force needed to shear a snake melon. The banana fruit exhibits high resistance to shear forces, as seen by the higher shear force of 48.06 N needed to shear it. Additionally, upon shearing the fruit of the snake melon, the average deformation was 8.37 mm. For the Agria potatoes variety, the deformation was 207.22 mm during quasi-static loading [39]. In the current investigation, a high deformation value of roughly 50 mm for potatoes suggested that they were very resistant to deformation during shearing. Also, the overall average maximum force of 754.49 N (Table 6) shows higher resistance of the potatoes cv. Spunta and their sensitivity to shear behavior. In addition, the overall average hardness was 20,132.03 (Table 6).
Overall, in order to minimize waste, the mechanical property results of this study are regarded as the fundamental data required for developing the machinery and equipment utilized in potato harvesting and post-harvesting processes. Additionally, the pressure forces created during the potato transfer and packaging must be decreased to the lowest rate possible (less than 8.8 N) in order to minimize mechanical damage and losses. One metric that can be used to gauge how hard the product’s tissue is its modulus of elasticity. The resultant tissue will be harder when the modulus of elasticity is higher [39].
4. Conclusions
To attain high quality standards for agricultural products like potatoes, one must first understand the significance of their mechanical and physical attributes and how these vary due to a range of circumstances. The study was carried out to recognize useful mechanical properties of potatoes cv. Spunta produced using a center-pivot irrigation system with three different tillage implements in a loamy sand soil. The mechanical properties were assigned using various indicators, such as modulus of elasticity, bioyield force, elastic and plastic ranges, rupture force, and hardness. These indicators were extracted from the force–deformation curves based on compression, penetration, and shear tests. The average maximum force of 754.49 N shows higher resistance of the potatoes cv. Spunta and their sensitivity to the shear behavior. This study showed significant differences in indicators extracted from compression and penetration tests depending on the tillage implemented in the seedbed preparation. In contrast, no considerable differences were found in indicators extracted from the shear tests. The findings of this study revealed that the disc harrow plow resulted in higher indicator values compared with the two other plows. This may be due to the effect of such a plow on the soil. Further extensive studies on other soil characteristics are required, and relating the results to the force–deformation analysis presented in this study may yield additional helpful information. In order to prevent product waste during potato storage, factory processing, and the use of agricultural machinery equipment, the mechanical properties should be adequately addressed when constructing washing, sorting, grading, and packaging equipment. Finally, the obtained results may be useful in determining the design and operating parameters of machines for harvesting, cleaning, sorting, and processing potato tubers in order to reduce both quantitative and qualitative losses.
S.S.A., S.A.A.-H., S.M.A.-S., A.M.A. and S.A.M.—conceptualization, methodology, analysis of the data, preparation of the figures and tables, funding acquisition, authoring and review of drafts of the paper, and approval of the final draft; S.A.A.-H. and A.M.A.—design and performance of the experiments. All authors have read and agreed to the published version of the manuscript.
Data are contained within the article.
The authors would like to extend their sincere appreciation to the Researchers Supporting Project (RSPD2024R752) at King Saud University, Riyadh, Saudi Arabia.
The authors declare no conflicts of interest.
Footnotes
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Enlarge this image.Figure 2. Measurements of the potato samples: length (L, mm); width (W, mm); and thickness (T, mm).
Enlarge this image.Figure 3. Measured force–deformation curve obtained from compression tests of potatoes cv. Spunta produced with a disc harrow plow.
Enlarge this image.Figure 4. Measured force–deformation curves obtained from penetration tests of potatoes cv. Spunta produced with the disc harrow plow.
Enlarge this image.Figure 5. Comparison of the mean values of maximum force (N) concerning the season and tillage implements of potatoes cv. Spunta gained from force–deformation curves of penetration tests. (In each column, the same uppercase letter indicates no significant difference concerning the tillage treatment, whereas the same lowercase letter indicates no significant difference concerning the season).
Enlarge this image.Figure 6. Comparison of the mean values of hardness (N·mm) of potatoes cv. Spunta gained from force–deformation curves of penetration tests concerning the season and tillage implements. (In each column, the same uppercase letter indicates no significant difference concerning the tillage treatment, whereas the same lowercase letter indicates no significant difference concerning the season).
Enlarge this image.Figure 7. Measured force–deformation curve obtained from shear tests of potatoes cv. Spunta produced with the disc harrow plow.
Characteristics of soil and water in the experimental site.
| Parameters | Soil | Water |
|---|---|---|
| Sand | 82.9 (%) ± 1.2 | ------ |
| Silt | 13.08 (%) ± 0.7 | ------ |
| Clay | 4.02 (%) ± 0.12 | ------ |
| Organic matter | 0.98 (%) ± 0.04 | ------ |
| Calcium carbonate | 6.85 (%) ± 1.1 | ------ |
| pH | 8.5 ± 0.1 | 7.57 ± 0.3 |
| EC | 4.6 (dS/m) ± 0.1 | 4.81 (dS/m) ± 0.2 |
| Na+ | 48.66 (ppm) ± 2.1 | 372.07 (mg/L) ± 1.2 |
| K+ | 4.91 (ppm) ± 0.12 | ------ |
| Ca++ | 140.59 (ppm) ± 3.15 | 404.75 (mg/L) ± 1.3 |
| Mg++ | 8.76 (ppm) ± 0.2 | 109.78 (mg/L) ± 1.1 |
| SO4 | 55.06 (ppm) ± 0.2 | 1237.6 (mg/L) ± 10.1 |
| Cl | 41.72 (ppm) ± 0.5 | ------ |
| NH3 | 19.61 (ppm) ± 0.13 | 8.11 (mg/L) ± 0.8 |
| TDS | ------ | 3204.79 (mg/L) ± 1.1 |
The significance probability for the mechanical properties obtained from compression tests of potatoes cv. Spunta produced with different tillage implements.
| Source of Variation | DF | Pr > F | |||||
|---|---|---|---|---|---|---|---|
| Modulus of Elasticity (N/mm) | Bioyield Force | Elastic Range | Rupture Point (N) | Plastic Range (mm) | Hardness (N·mm) | ||
| (N) | (mm) | ||||||
| Planting season | 1 | 0.9963 | 0.8017 | 0.0511 | 0.0757 | 0.1262 | 0.8076 |
| Tillage implements | 2 | <0.0001 | <0.0001 | <0.0001 | <0.0001 | <0.0001 | <0.0001 |
| Planting season × Tillage implements | 2 | 0.9997 | 0.7196 | 0.9787 | 0.8633 | 0.9616 | 0.8669 |
DF: Degree of freedom.
Comparison of the mean * values of the mechanical properties of potatoes cv. Spunta concerning season and tillage implementation. The values were gained from force–deformation curves obtained from compression tests.
| Mechanical Properties | Planting Season | Tillage Implements | |||
|---|---|---|---|---|---|
| DH | CHP | MBP | Overall Average | ||
| Modulus of elasticity (N/mm) | First | 5.88 A,a ± 0.29 | 4.47 B,a ± 0.52 | 4.22 B,a ±0.33 | 4.89 ± 0.88 |
| Second | 5.89 A,a ± 0.28 | 4.66 B,a ± 0.49 | 4.22 B,a ± 0.32 | ||
| Bioyield force (N) | First | 113.45 A,a ± 3.33 | 94.82 B,a ± 4.03 | 85.59 C,a ± 1.95 | 97.83 ± 14.67 |
| Second | 114.12 A,a ± 2.94 | 94.77 B,a ± 3.84 | 84.25 C,a ± 2.01 | ||
| Elastic range (mm) | First | 3.52 A,a ± 0.008 | 2.76 B,a ± 0.010 | 2.73 C,a ± 0.015 | 3.00 ± 0.45 |
| Second | 3.51 A,a ± 0.010 | 2.75 B,a ± 0.009 | 2.72 C,a ± 0.013 | ||
| Rupture point (N) | First | 139.79 A,a ± 3.20 | 115.70 B,a ± 1.86 | 102.86 C,a ± 1.78 | 118.75 ± 18.91 |
| Second | 138.58 A,a ± 2.98 | 114.69 B,a ± 2.13 | 100.90 C,a ± 1.22 | ||
| Plastic range (mm) | First | 2.50 A,a ± 0.008 | 1.96 B,a ± 0.01 | 1.94 C,a ± 0.011 | 2.13 ± 0.32 |
| Second | 2.49 A,a ± 0.007 | 1.95 B,a ± 0.01 | 1.93 C,a ± 0.010 | ||
| Hardness (N·mm) | First | 1952.29 A,a ± 35.33 | 1627.92 B,a ± 16.68 | 1437.76 C,a ± 25.98 | 1671.52 ± 257.46 |
| Second | 1943.08 A,a ± 34.11 | 1629.57 B,a ± 14.52 | 1438.52 C,a ± 24.15 | ||
* For each mechanical property, the same uppercase letter indicates no significant differences in row values, whereas the same lowercase letter indicates no significant difference in the column values.
The significance probability for the mechanical properties from penetration tests of Spunta cv. potatoes produced with different tillage implements.
| Source of Variation | DF | Pr > F | |
|---|---|---|---|
| Maximum Force (N) | Hardness (N·mm) | ||
| Planting season | 1 | 0.2105 | 0.8075 |
| Tillage implements | 2 | <0.0001 | <0.0001 |
| Planting season × Tillage implements | 2 | 0.9677 | 0.867 |
DF: Degree of freedom.
The significance probability for the mechanical properties obtained from the shear tests of potatoes cv. Spunta produced with different tillage implements.
| Source of Variation | DF | Pr > F | |
|---|---|---|---|
| Maximum Force (N) | Hardness (N·mm) | ||
| Season | 1 | 0.4432 | 0.3463 |
| Tillage implements | 2 | 0.909 | 0.0641 |
| Season × Tillage implements | 2 | 0.8477 | 0.9306 |
DF: Degree of freedom.
Mean values of the mechanical properties of potatoes cv. Spunta gained from force–deformation curves of shear tests concerning the season and tillage implements.
| Mechanical Properties | Planting Season | Tillage Implement | |||
|---|---|---|---|---|---|
| DH | CHP | MBP | Ovrall Average | ||
| Maximum force (N) | First | 750.36 ± 205.01 | 772.67 ± 137.58 | 842.43 ± 319.49 | 754.49 ± 37.09 |
| Second | 706.36 ± 138.49 | 750.67 ± 91.53 | 704.43 ± 389.44 | ||
| Hardness (N·mm) | First | 21,428.12 ± 994.45 | 19,747.17 ± 1825.30 | 19,915.30 ± 1141.87 | 20,132.03 ± 821.28 |
| Second | 20,728.12 ± 648.83 | 19,478.17 ± 1584.90 | 19,495.30 ± 1326.60 | ||
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1 Department of Agricultural Engineering, College of Food and Agriculture Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia;
2 Deanship of Scientific Research, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia;