Progress in Mechanized Harvesting Technologies and Equipment for Minor Cereals: A Review

Abstract

Minor cereals are an important part of the Chinese grain industry, accounting for about 8 percent of the country’s total grain-growing area. Minor cereals include millet, buckwheat, Panicum miliaceum, and other similar grains. Influenced by topographical and climatic factors, the distribution of minor cereals in China is mainly concentrated in the plateau and hilly areas north of the Yangtze River. In addition, there are large concentrations of minor cereals in Inner Mongolia, Heilongjiang, and other areas with flatter terrain. However, the level of mechanized harvesting in these areas is still low, and there is little research on the whole process of mechanized harvesting of minor cereals. This paper aims to discuss the current status of the minor cereal industry and its mechanization level, with particular attention to the challenges encountered in research related to the mechanized harvesting of minor cereals, including limited availability of suitable machinery, high losses, and low efficiency. The article provides a comprehensive overview of the key technologies that must be advanced to achieve mechanized harvesting throughout the process, such as header design, threshing, cleaning, and intelligent modular systems. It also summarizes current research progress on advanced equipment for mechanized harvesting of minor cereals. In addition, the article puts forward suggestions to promote the development of mechanized harvesting of minor cereals, focusing on aspects such as crop variety optimization, equipment modularization, and intelligentization technology, aiming to provide a reference for the further development and research of mechanized harvesting technology for minor cereals in China.

1. Introduction

In recent years, the Chinese government has demonstrated a renewed commitment to ensuring food security. Document No. 1 of the 2024 Chinese Central Committee underscores the significance of integrated agriculture and food security management, emphasizing the necessity of diversifying food sources and expanding through multiple channels [1,2]. This emphasis signifies a notable strengthening of the role of minor cereals, a sector within the food industry, within the national food security strategy. The term “minor cereals” encompasses a diverse array of small grains and legume crops, in addition to major grains such as rice, wheat, corn, soybeans, and potatoes, among other bulk food crops. These include millet, buckwheat, Panicum miliaceum, and sorghum, which are particularly prominent in arid and alpine regions of China [3]. Current statistics indicate that the area dedicated to minor cereal cultivation in China remains approximately 9 million hectares, with a total production ranging from 17 to 20 million tons [4]. The harvesting methods employed for these grains in China can be categorized into three distinct approaches: combined harvesting, segmented harvesting, and manual harvesting. The selection of a particular method is influenced by factors such as the scale of cultivation, the prevailing geographical environment, and other considerations. The distribution of minor cereals in China is predominantly concentrated in hilly and mountainous regions, with manual harvesting constituting the predominant harvesting method [5]. Manual harvesting of minor cereals is characterized by high labor intensity, significant labor cost, and a protracted harvesting cycle. These factors have impeded the development of the Chinese domestic minor cereal industry. Consequently, the development of mechanized combined harvesting technology for minor cereals is imperative to address these challenges.

Mechanized harvesting technology for minor cereals is a combined harvesting technology that integrates sorting, cutting, threshing, clearing and separating, collecting, and shipping [6]. Achieving full mechanization of the entire industrial chain for minor cereals harvesting can significantly reduce economic costs and promote the development of agricultural systems.

Since the 1990s, there has been an increase in demand for large-feeding harvesters. In response, combine manufacturers worldwide have increased their research and development of large-feeding self-propelled combines. These developments have included the use of turbine engines and the adjustment of other mechanical structural parameters. As a result, the feeding capacity of minor cereal combines has increased significantly, and at the same time, the size of the harvester has increased substantially. Into the 21st century, advancements in hydraulic drive technology and electronic monitoring technology have led to the integration of these technologies into combine harvesters, propelling the development of large self-propelled combine harvesters towards intelligence, thereby significantly reducing labor intensity. In China, the absence of a robust technical foundation has hindered the development of small and medium-sized grain combine harvesters that can adequately meet market demands. To address this gap, alternative approaches have been employed, such as the modification of the header, adjustment of equipment parameters, and the implementation of dedicated minor cereal harvesting models. Additionally, the sporadic distribution of minor cereals in hilly regions, coupled with their relatively limited area of cultivation, has led to a stagnant state in the research and development of large-scale minor cereal combine harvesters.

This paper provides an overview of the planting distribution characteristics of millet, buckwheat, Panicum miliaceum, and other minor cereals in China, as well as the mechanization levels in their major production areas. It focuses on the key technologies and full-scale equipment for the mechanized harvesting of minor cereals worldwide. In addition, considering the technological requirements and challenges associated with the combined mechanized harvesting of minor cereals, the paper explores the development direction of mechanized combined harvesting technologies for minor cereals, with the goals of low loss and high purity, to provide theoretical references for further development and research.

2. Status of the Minor Cereal Industry in China

2.1. Distribution and Scale of Minor Cereal Cultivation

Minor cereals are cultivated across the globe, with particular prevalence in certain plateau regions, ecologically disadvantaged areas, and economically underdeveloped regions. In these areas, minor cereals serve as a crucial source of sustenance for humans and a significant cash crop [7]. In China, the primary regions where minor cereals are cultivated are plateau areas, including the Loess Plateau, Inner Mongolia Plateau, Yunnan–Guizhou Plateau, and Qinghai–Tibetan Plateau. These regions are particularly conducive to the cultivation of small minor cereals, which exhibit characteristics such as short fertility, drought tolerance, and resistance to barrenness and cold conditions, as a result of the inherent limitations of the soil and arid climate [8].

As shown in Figure 1, the planting area and production of minor cereals across the country from 2019 to 2024 are depicted based on the annual grain production data released by the National Bureau of Statistics of China. The data were obtained from the official website of the National Bureau of Statistics. A dual-axis line chart was constructed using Origin software (Version 2024) to visualize the trends in planting area and production of minor cereals over the specified period.

Minor cereal cultivation is predominantly concentrated in the arid and semi-arid regions of the northeastern and northwestern regions of China, as well as the northern regions [9]. In 2020, the area dedicated to cereal cultivation in China was estimated to be approximately 1.5 million hectares, with an estimated total output of approximately 9 million tons [10]. According to the data from the 2022 China Rural Statistical Yearbook, the millet production in various provinces of China in 2021 is shown in Figure 2 (data for Shanghai, Zhejiang, Fujian, Jiangxi, and Tibet are not available).

Buckwheat is classified into two distinct categories: sweet buckwheat and buckwheat. The geographical distribution of buckwheat varies significantly across China. The Huaihe River and the Qinling Mountains regions are notable for their significant buckwheat production, particularly in the southern reaches of these areas, where the terrain is predominantly mountainous and hilly, bordering the extensive Yunnan–Guizhou–Chuan plains. The northern Qinhuai line is predominantly characterized by buckwheat cultivation, with a notable presence in the northern Loess Plateau and the Inner Mongolia Plateau, encompassing the central and southeastern regions [11]. China stands as the sole nation engaging in large-scale buckwheat cultivation on a global scale, with an estimated area of approximately 300,000 hectares, yielding an annual production ranging from 300,000 to 500,000 tons [12]. The cultivation area for buckwheat is approximately 700,000 hectares, with an estimated production of 750,000 tons [13].

In contrast, Panicum miliaceum is predominantly cultivated in northern Shaanxi, northwestern Jin, northern Jibei Dam, Ningxia, Gansu, Inner Mongolia, and northeastern China, with a planting area of approximately 600,000 hectares and a total output of about 1.35 million tons [14,15].

2.2. Status of Mechanized Harvesting of Minor Cereals

Minor cereals are widely distributed in China, and the degree of mechanization of minor cereal harvesting is higher in areas with contiguous land, such as Northeast China and Xinjiang. In contrast, Northwest China, Central China, and Southwest China are mostly gently sloping and hilly, with a lower degree of mechanization [16].

Since the 13th Five-Year Plan, China has achieved a domestic integrated mechanization rate of 71.25% for crop cultivation, planting, and harvesting. Regionally, mechanization has developed more rapidly in the northern plains, while the integrated mechanization rate in the southern regions, particularly in the southwestern hilly areas, remains below 50% [17].

The mechanized harvesting technology for major grain crops, including rice, wheat, and corn, has achieved a certain level of maturity. However, the harvesting and threshing of minor cereals remains predominantly in the manual and animal operation stage, significantly hindering the development of the minor cereal industry [18].

3. Key Technologies for Mechanized Harvesting of Minor Cereals

3.1. Crop Cutter Equipment and Key Technologies

3.1.1. Efficient Separating Crop Organization

Separating crops is the first step in harvesting minor cereals, and the key component is the crop separator. During field operations, there are problems such as the low-hanging and entangled panicles of millet and the intertwined plants of buckwheat, which cause mutual collisions and separation of the plants. The rational arrangement of the shape and distribution of the crop separator has an important impact on solving the above problems. It is necessary to study the influence trend of the forward inclination angle, separation angle, tip height from the ground, and arrangement spacing of the crop separator on the separation effect, in order to optimize the design of the structure and spacing of the crop separator, and thus design an efficient crop separation mechanism. At present, the shape design of crop separators includes semi-conical, four-pronged [19], conical spiral churn structure [20], winnowing fan shape and grid format [21], which have met the actual needs on a basic level. On the other hand, there are many types of small grains. To achieve the multi-purpose use of a single machine, which involves using the same machine to harvest different varieties of a single crop or multiple different crops by simply replacing some functional components, a crop separation device with adjustable spacing can be designed to reduce the manufacturing cost of the cutting platform.

3.1.2. Low-Loss Feeding Technology for Crop-Supporting Devices

Feeding is an important process in the workflow of small-grain combine harvesting. During the feeding process, the collision and cutting by the reel, as well as the vibration of the cutting platform, exacerbate the occurrence of losses. Studies have shown that losses in the cutting platform account for 40% of the total harvesting losses [22]. At present, most small-grain combine harvesters in use are modified from rice and wheat combine harvesters. Large combine harvesters mostly use reels, while small combine harvesters use crop support devices. The functions of the reel and the crop support device are roughly the same. Both guide the stalks towards the cutting blade and support the stalks during cutting. After the stalks are cut, they push the stalks to the conveyor to avoid stalk accumulation at the cutting blade [23]. The difference is that the reel has a simple structure and lower cost, while the crop support device can better straighten and lift lodged crops [24].

As the most commonly used crop-supporting device, the header wheel should be analyzed for the relevant traits of minor cereals to solve the problems of easy shattering after maturity, stem entanglement, and losses caused by the impact of the header wheel. It is necessary to study the effects of header reel speed, number of tines, tine shape, and crop entry angle on the loss rate and develop a new type of low-loss header reel mechanism suitable for complex traits.

The commonly used reaper wheel structures include the plate-type and finger-rod type. In addition, in the studies [25,26], an eccentric rotating crop-supporting wheel was specifically designed to improve the harvesting effect of lodged crops. This design employs a multi-link mechanism structure, which allows the tines to flip and retract after lifting the lodged crops, thereby preventing entanglement of crop stalks. Subsequently, the tines quickly move forward to prepare for the next cycle of supporting lodged crops. The structural principle diagram is shown in Figure 3.

The crop-supporting device is another important type of crop-supporting mechanism, mainly applied in small and medium-sized combine harvesters. Depending on the application scenarios, researchers have designed different types of crop-supporting devices. Specifically, the existing crop-supporting devices are divided into three categories, namely the vertical plane type, the inclined plane type, and the star wheel type [27].

3.1.3. Cutter

The working width of a minor cereal combine harvester is substantial, and the harvesting process often involves the utilization of a reciprocating cutter to sever the crop stalks. The cutter is composed of a moving blade, knife bar, fixed blade, pressure edge, gasket, upper and lower friction blades, and additional components. The cutting mechanism involves a dynamic blade and a fixed blade, with the fixed blade and edge protector functioning as the two support points. The dynamic blade, positioned between the two support points, executes a reciprocating cutting movement at a specific velocity. The relationship between the cutter stroke, moving blade, and fixed blade spacing is a critical factor in the classification of harvesting mechanisms. These mechanisms can be categorized into three primary types: standard, double-blade distance, and low-cutting. It is noteworthy that combine harvesters typically employ the standard-type cutting mechanism. The Chinese national standard further subdivides the standard-type cutting mechanism into type 1, type 2, and type 3 cutters [28]. In addition to these conventional cutters, researchers have optimized the cutter forms based on the principle of bionics. Typical bionic examples and characteristics are shown in

Table 1. Typical biomimetic examples and their characteristics.

Name	Bionic Design Process			Characteristics
Tenebrae Upper Jaw Reciprocating Bionic Cutter [19,29,30]				The extraction of the tooth profile curve of the upper jaw cutting tooth part of the aspen revealed a stalk leakage rate of 2.5% in the field test. This reduction in leakage rate, coupled with a decrease in cutting resistance and an enhancement in cutting efficacy, was observed in comparison to the conventional cutter.
Locust Bionic Cutter [31,32]				The bionic disc cutter demonstrated an 18.49% reduction in power consumption when evaluated for its effectiveness in cutting corn stover.
Leaf cutter ant bionic cutter [33]				The experimental findings demonstrated that the maximum shear force of the bionic blade was reduced by 7.74%, in comparison with the conventional blades. Furthermore, the maximum shear force was reduced by 8.84%.
Cricket mouthparts maxillary bionic cutter [34,35]				The two bionic cutters were utilized in cutting experiments on stalks. The former exhibited robust cutting performance, exhibiting an 18% reduction in maximum shear force and a 15.8% reduction in cutting power consumption. The latter demonstrated superior cutting efficacy, exhibiting an average cutting force of 9.193 N and a cutting power of 1.215 J. The latter exhibited superior cutting performance.
Chewing Mouthpiece Upper Jaw of Korean Golden Turtle [36]				The bionic cutting device has been demonstrated to reduce the blanking zone by 50% and the re-cutting zone by 80%, which is significantly better than the traditional standard-type cutter.

.

3.1.4. High-Efficiency, Low-Loss Flexible Header

The header section of the combine harvester for minor cereals is the component where significant losses occur during the entire harvesting process. A good harvesting effect can only be achieved through the rational combination of components such as the header reel, crop-supporting device, cutter, and spiral conveyor on the header. Worldwide, research on headers is increasingly moving towards intelligentization, and many efficient and low-loss harvesting headers have been designed. The development of combine harvesters for minor cereals started earlier internationally, and the intelligentization technology of headers was more advanced. For example, the two high-performance harvesters NEW HOLLAND CX5000 and CX6000 produced by New Holland Agricultural Machinery Company (USA) both adopt the AUTO FLOAT TM II system, as shown in Figure 4. This system can correct the exaggerated weight system, preventing the header from dragging on the ground when working downhill and maintaining the correct stubble height when working uphill. New Holland Company (USA) has also independently developed the Varifeed^TM grain header, which can achieve a free adjustment distance of 500 mm for the cutter, ensuring normal cutting efficiency under various conditions.

To adapt to different terrains and crop distributions and reduce missed cutting and losses, researchers have also designed flexible cutterbars [37]. Flexible header refers to a type of cutting header designed with adjustable components and mechanisms that allow it to adapt to varying terrain contours and crop conditions. These cutterbars rely on high-precision sensors, optimized control algorithms, and intelligent detection devices to achieve precise control of the cutterbar height and shape through hydraulic systems and floating knives, thereby reducing crop losses [38]. For example, the Case 3020 flexible grain cutterbar from Case Company, USA is equipped with a TerraFlex™ knife float device, has a cutting width of up to 7600 mm, and exhibits good contour-following performance. In 2014, Zoomlion Company in Hunan, China developed the Grain King 8000A multi-functional high-capacity combine harvester, which is also equipped with a 5.4-m flexible cutterbar that can adapt to multi-terrain and multi-crop combined harvesting. The Grain God GM100 series axial-flow wheeled grain combine harvester produced by Leiwo Company in Shandong, China can be fitted with various types of cutterbars for harvesting millet, sorghum, rapeseed, and other types of minor cereals, saving harvesting costs and achieving good economic effects. Zhao Jing’s [39] research team designed a 4LZ-1.5 millet combine harvester with an automatic electronic control system for the cutterbar, which can achieve stepless precise adjustment of parameters such as header wheel speed and header height. It can also quickly adjust the cutting speed of the cutterbar, machine forward speed, drum speed, and cutterbar ground clearance according to the height of the millet to be harvested, straw moisture content, lodging degree, and crop yield, keeping the cutterbar always at the best working level.

3.2. Key Technologies for Mechanized Threshing of Minor Cereals

Threshing is one of the most important aspects in the harvesting process of minor cereals. The design of the threshing mechanism requires the separation of as many seeds as possible from the pod, broken stalks, and other impurities. The most basic structural form consists of a high-speed rotating drum and a fixed concave plate. The drum is designed with threshing elements such as rasp bars, nail teeth, and bow teeth according to the requirements, and the threshing mainly relies on the principles of impact, rubbing, and brushing. Compared with other cereals, minor cereals have special panicle shapes and small seed radii, making threshing more difficult. During machine threshing, there are often “small grain clusters” that are not completely threshed, commonly known as “grain bunches,” which can only be resolved through secondary threshing. At present, the harvesting of minor cereals still largely relies on manual cutting and drying, followed by threshing using specialized minor cereal threshers [40].

In the research on threshing technology of combine harvesters for minor cereals, researchers mainly focus on four aspects [41]. First, the movement and force analysis of materials inside the threshing device. The impact of different forms of forces on threshing performance is examined. Second, the threshing and separation mechanism. The physical parameters of minor cereal seeds, stalks, pods, etc., are measured, and the relationship between these parameters and threshing forms, as well as separation efficiency, is studied. Third, the threshing and separation model and the distribution pattern of threshed materials. The proportion of each component in the fed materials is analyzed, a threshing and separation model is established, and its relationship with separation performance is investigated. Fourth, the structure and working parameters of the threshing device. The influence of the threshing drum structure in the threshing mechanism, drum speed, the size and distribution of threshing gaps, and the types and distribution of threshing teeth on the drum on threshing effectiveness is explored [42].

3.2.1. Combined Threshing Drum Unit

Common threshing drums are classified into different types based on the tooth shape, such as striped rod type, nail tooth type, bow tooth type, and plate tooth type. In addition, there are less commonly used threshing drums like the cylindrical rod tooth type, the elbow rod tooth type, and the blade-tooth type. Building on this, researchers, considering the unique advantages of different tooth-shaped threshing drums, have designed combined threshing drums, which increase the drum length and allow for more thorough separation of materials. The combined threshing drums designed at the current stage are shown in

Table 2. Combined threshing drum unit.

Type		Features	Schematic Diagram of Structure	Applicable Scope
Ribbed rod-nail tooth threshing drum	Standard type	The material enters the drum axially and subsequently passes through the ribbed rod section and the nail tooth section. In comparison with the full nail tooth drum, the striking capacity is weaker, the loss rate is higher, and the power consumption is higher; however, the impurity content is lower [43].		The implement is generally suitable for the threshing and separation of grains.
	Short ribbed rod-nail tooth type	The anterior portion of the drum is equipped with ribbed rod blocks, which primarily function as threshing mechanisms, while the posterior section is fitted with nail teeth that facilitate churning and separation processes, in addition to threshing functions [44]. The integration of these two distinct tooth types, in conjunction with spiral rows, enhances the conveying capacity, increases the axial size, and optimizes the separation efficiency.		It is particularly well-suited for crops with high moisture content and is characterized by its ease of breakage, a trait that is advantageous in the processing of corn.
Ribbed rod-rod tooth threshing drum	Standard type	The initial segment corresponds to the ribbed rod portion, which constitutes the primary phase of threshing. The subsequent segment, known as the rod-tooth portion, functions to facilitate the separation of kernels ensconced within the stem layer [45].		It has been demonstrated to be suitable for legumes with low water content [46].
	Ribbed rod-telescopic rod tooth type	The ribbed rod constitutes the primary component responsible for the threshing process. During the rotational movement, it propels the rod teeth, which are articulated with it, to execute a reciprocating telescopic movement. This movement subsequently exerts an impact on the material, causing it to be knocked. As the rod teeth rotate and expand, the material undergoes a tumbling and backward propulsion to prevent material blockage [47].		This implement is particularly well-suited for buckwheat and other crops that pose significant challenges during the threshing process.
Short ribbed rod-plate tooth type		The short ribbed rod and plate teeth are integrated into a unified threshing unit, which is meticulously arranged on the threshing drum in an even and linear fashion. This configuration effectively reduces the debris content of the threshed material, thereby ensuring a uniform distribution [48].		The implement is generally suitable for the threshing and separation of grains.
Short ribbed rod-bow tooth type		The configuration of the ribbed rod blocks and bow teeth is such that the first half of the ribbed rod blocks and bow teeth are staggered in rows, and the second half consists of bow teeth and a separating plate. This configuration has been shown to result in a reduction in the crushing rate, an increase in the stripping rate, and a reduction in entrainment loss.		The cultivation of sorghum is well-suited for this purpose.
Main and auxiliary nail tooth type		The combined axial flow threshing drum is characterized by its integration of a fixedly mounted main nail tooth on the cylinder shaft, a type of main tooth seat, and a secondary nail tooth that is inserted and fitted into a limiting slot [49]. This configuration is notable for its simplicity and effectiveness in reducing seed entrainment losses.		The machine is designed for the efficient threshing and separation of grains with high moisture content, as well as for addressing issues of significant sticky entrainment of seeds.

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In addition to the aforementioned threshing element combination structures, researchers also conceptualized a threshing drum structure comprising three threshing elements, employing the experimental SXF-85CD broad bean harvester produced by Shiyan Shuangxing Company, located in Hubei Province, China, as a case study [50]. The structural design is depicted in Figure 5.

The experimental threshing drum is divided into four sections, namely the combing section, threshing section, separating section, and straw walking section, in sequence from front to back. The combing section features a ripple structure, which serves to thin out the material. The threshing section is equipped with a bow-tooth structure and is the primary stage for fava bean threshing and separation. The separating section has an alternating arrangement of rod teeth and bow teeth, mainly used to separate fava beans from stalks after threshing. The final straw walking section is composed of rod teeth, which have a strong grasping ability and complete the final separation. Experimental results indicate that the combined threshing drum significantly outperforms the traditional all-rod-tooth threshing drum in terms of various evaluation indicators.

3.2.2. Multi-Drum Combination Threshing Unit

Double-drum and multi-drum combination threshing devices are critical methods to enhance the cleaning rate and reduce the loss rate. Concurrently, such devices can also augment harvesting efficiency and mitigate grain damage. The direction of material movement within the threshing device can be categorized into four distinct types: tangential flow, longitudinal axial flow, transverse axial flow, and tangential flow in combination with the latter two. The following table (

Table 3. Double and multi-drum combination threshing units.

Type	Characteristics	Schematic Diagram of Structure	Application Scenario
Tangential flow-type double drum threshing device	The configuration of the drums is such that they are arranged parallel to each other from front to back. The drum at the front is typically a peg-tooth drum, which possesses a high threshing capacity. In contrast, the drum at the rear is of a ripple-type design [51].		This configuration is frequently utilized in harvesters that process substantial feed volumes.
Longitudinal flow double drum threshing device	The machine consists of two threshing drums with different structures and motion parameters at the front and rear [52]. It features an axial flow of grain and a long threshing stroke, as well as a long threshing time and good separation performance.		The utilization of this technique is particularly recommended for miscellaneous crops that are more challenging to thresh and separate.
Tangential flow + double longitudinal flow threshing device	The integration of tangential and longitudinal axial flow technologies is a recent development in agricultural machinery. The design consists of a tangential drum at the front and two axial flow drums at the rear, arranged side by side. This configuration allows for the effective separation of high-yield crops that are difficult to thresh [53]. The result is an improvement in crop harvesting efficiency and threshing quality.		A representative model of this structure is the John Deere C230 combine [54].
Tangential flow + double transverse axial flow threshing device	The system under consideration utilizes a configuration of three threshing drums, comprising one tangential flow and two axial flows. In comparison with the tangential axial flow two-drum structure, this configuration has been demonstrated to exhibit superior operational efficacy [55].		It is suitable for harvesting oilseed rape as well as other miscellaneous crops.
Multi-stage tangential feed threshing drum + double longitudinal flow threshing device	The apparatus under consideration is composed of two tangential flow feeding drums and one tangential flow threshing drum. The latter is situated centrally between the two feeding wheels. In the posterior section, two longitudinal axial flow threshing and separating drums are arranged laterally.		As indicated in [54], this element is typically identified in substantial longitudinal flow harvesters of the CLASS category.

) enumerates five exemplary combined threshing devices.

3.3. Mechanized Sorting Technology for Minor Cereals

Cleaning constitutes the third link in the mechanized harvesting of minor cereals, with the objective being the separation of seeds from detritus. According to the principle of separation, cleaning can be categorized into three distinct categories: firstly, there is the aerodynamic principle of cleaning, in which a fan generates a specific speed of airflow, thereby enabling impurities to overcome their gravitational forces and suspend, thus facilitating the separation of seeds and impurities. The second category, which adheres to the principle of airflow rotation and centrifugal force, typifies the mechanism of the cyclone separator. In this configuration, the material exits the cyclone at a tangential velocity, guided along the side wall. The separation of the cylinder is achieved by the action of the rotating airflow, causing the grain to move in a downward direction and fall into the grain box. The lighter impurities and short stalks are suspended in the airflow from the suction fan, which is discharged [56]. The cyclone separator has a simple structure, a high cleaning rate, and low grain loss. It is commonly used in small-grain combine harvesters for cleaning and separating.

The third category employs airflow in conjunction with a sieve to facilitate cleaning, which is the most prevalent cleaning device for minor cereal combine harvesters. At this stage, two predominant structures are observed according to this principle of cleaning: fan-vibrating sieve and fan-cylinder sieve [57]. In the fan-vibrating screen, the fan airflow counteracts the weight of the material, maintaining it in an evacuated state. The screen mesh is constantly vibrating, causing the seeds to fall through the mesh into the collection box. The separated impurities are carried out of the chassis by the airflow. The classification of the fan-vibrating screen can be categorized into four types, namely, single duct fan single-deck vibrating screen, single duct fan double-deck vibrating screen, double duct fan double-deck vibrating screen, and double fan double-deck vibrating screen [58]. A recent development in the field involves the design of a clearing device with multiple ducts and multiple screens, which has been shown to enhance the clearing effect of the seeds. A notable example is the Warde Ruilong 4LZ-2.0E combine harvester (classic version), developed by Shandong Warde Company in China, which employs a centrifugal fan and a vibrating screen in a single apparatus. This model features three internally configured airflow ducts, thereby regulating the wind volume and direction. These features allow for efficient cleaning, with the two-layer fish scale sieve vibrated reciprocally to enhance cleaning efficiency. Additionally, a shaking plate is incorporated to ensure uniform material entry into the cleaning device [59]. The structure of the cleaning device is illustrated in Figure 6.

In addition to the aforementioned models, the following models utilize a multi-duct and multi-screen structure as the clearing device, including the 4LZ-10M6 and 4LZ-2 harvesters developed by Shandong Weichai Leiwo Company in China, the 4LZ-8Z self-propelled combine harvester, 4LZG-1.5 and 4LZG-3.0 grain harvesters developed by Shandong Jindafeng Company in China, the 4LGZ-4.0Z self-propelled grain harvester developed by Beijing Zhongnong Group in China, the MC H80 PLUS+ version harvester developed by CLAAS Agricultural Machinery Company, and the C100 W100 grain combine developed by John Deere Company in Illinois, USA.

In the fan-cylinder sieve structure, once the material enters the sieve cylinder, the cylindrical sieve mesh undergoes rotation, thereby subjecting itself to centrifugal force and the filtering effect of the sieve mesh. This process enables the separation of seeds and impurities. The cylindrical sieve is designed with an inclination, which, in conjunction with the fan airflow, results in the accumulation of light stalks that remain and the expulsion of impurities from the chassis. In the context of actual harvesting operations, the utilization of double-layer cylindrical sieves or multi-layer cylindrical sieves is prevalent. These sieves possess internal and external mesh apertures that differ, thereby ensuring that the material undergoes dual cleaning, thus enhancing the efficiency of the cleaning process. These devices are employed in the 4LZ-2A combine harvester, a product of Leiwo Gushen Company, in Shandong, China, as well as the company’s Golden Eagle crawler-type full-feed grain harvester. These two models utilize a double fan configuration augmented by a double-layer cylindrical sieve structure, complemented by the incorporation of a vibrating tail sieve cleaning device, thereby ensuring a secondary cleaning and enhancing the efficacy of the harvesting process.

3.4. Multi-Functional Chassis Travel System

The travel systems of minor cereal harvesters mainly adopt two types: wheeled and tracked [60]. Wheeled travel systems are further divided into front-wheel drive and four-wheel drive configurations. Currently, the front-wheel drive structure is more commonly used in wheeled travel systems. Some new types of grain harvesters have also adopted electric travel chassis. This design uses a hydrostatic drive system, combined with a gearbox and final drives, allowing free switching between two-wheel and four-wheel drive modes, thereby enhancing the machine’s flexibility and adaptability [61]. Tracked travel systems can be divided into full-tracked and half-tracked structures. Since the full-tracked travel system is more versatile than the half-tracked one, full-tracked structures are more widely used as travel systems in domestic minor cereal harvesters in China.

In recent years, scholars from around the globe have delved into the domain of agricultural undercarriage technology, particularly in the context of hilly and mountainous terrain [62,63,64,65,66]. The front-drive wheeled travel system has a low cost and is relatively widely used, as evidenced by the Massey Ferguson MF-T7 combine harvester, the Zoomlion Harvest 2022 model 4LZ-9B self-propelled full-feed grain combine harvester, and the Zoomlion 4LGZ-4.0Z. The adoption of a front-drive wheeled structure as the traveling system is also evident in the John Deere W70/W80/W100 series, Chunyu MC H80 PLUS+, Foton Lever Gushen 4LZ-2 grain combine harvester, and other models. The adoption of a four-wheel drive-wheeled structure incurs a relatively high cost and is less prevalent in China. The Leiwo Gushen 4LZ-10M6 series harvester employs a four-wheel drive system, offering both mechanical and hydraulic options. The harvester features four-wheel steering with cross-country tires, ensuring high reliability and a turning radius of less than 6 m, thereby ensuring excellent maneuverability. International models equipped with four-wheel drive include the CASE IH AXIAL-FLOW 4000 series grain combine harvester, the NEW HOLLAND CX5000/CX6000 series harvester, and other models. The full-track structure, exemplified by the 4LZT-7ZB and 4LZT-7ZB1 series combine harvesters manufactured by Zoomlion Agricultural Machinery Company in Anhui, China, incorporates an elongated and high-flower track structure with a track gauge of 1250 mm, thereby achieving higher ground clearance and enhanced passing performance. In contrast, the half-track structure has seen a comparatively limited adoption on an international scale. A notable example is John Deere’s S770 harvester, which utilizes a rubber half-track structure equipped with a closed oil bath system and four layers of steel cord within the rubber. This configuration enables the dissipation of heat during operation at high speeds, enhancing the tracks’ adaptability, stability, and reducing maintenance requirements.

3.5. Intelligent Technologies

Intelligent technologies refer to the integration of advanced computational systems, sensors, and automation techniques that enhance the efficiency, precision, and sustainability of agricultural operations. The development of modern agriculture is contingent upon agricultural machinery and equipment, which serve as the fundamental basis for achieving agricultural modernization. The integration of the Internet of Things, artificial intelligence, big data, and other emerging technologies with agricultural production has led to a new era of networked, digital, and intelligent development in agriculture [67]. However, it should be noted that Chinese research in the field of intelligent agricultural machinery and equipment is still in its nascent stages, exhibiting significant disparities in technological sophistication when benchmarked against global leaders [68]. The intellectualization of minor cereal harvesting equipment holds significant potential for enhancing work efficiency and grain quality, while concurrently reducing production costs. This is particularly evident in the domains of minor cereal harvesting, threshing, conveying, clearing, assembling, and other processes. The benefits of this intellectualization include a reduction in mechanical damage and impurities, the monitoring of implement operation, adaptive parameter adjustment, enhanced driving comfort, and other advantages [69,70,71,72]. The following intelligent technologies have been developed and employed.

The intelligent cutting device employs an intelligent electric control system that optimizes adjustment according to the actual characteristics of the minor cereal crops to be harvested, thereby reducing harvesting losses. A 4LZG-1.5-type grain combine harvester, for instance, can achieve stepless precise adjustment of the rotation speed of the plucking wheel and the height of the plucking wheel. The harvesting speed, forward speed, drum speed, and cutting platform clearance are all parameters that can be adjusted with precision, by the height of the grain, the moisture content of the straw, the degree of collapse, and the crop yield. The prototype was tested for millet harvesting in the field in Hebei Province, China, in 2019. The total loss rate was measured at 4.5%, the impurity content at 2.2%, and the seed damage rate at 3.1%. The harvesting performance was satisfactory. The CX5000/CX6000 series of combine harvesters, designed by the CNH Industrial China Branch in Shanghai, adopts the AUTO FLOAT TM II system, which was developed in-house. This system corrects the exaggerated weight system, thereby preventing the cutter from pushing against the ground when working downhill and maintaining the correct stubble height when working uphill.

The intelligent cleaning device is a sophisticated piece of equipment that utilizes advanced technology to optimize various parameters during the cleaning process. These parameters, which include fan power, screen vibration frequency, and vibration amplitude, are adjusted through the measurement of data to minimize seed loss. The monitoring components employed in this process are outlined in

Table 4. Commonly used monitoring elements in scavenging devices.

Monitoring Device	Schematic Diagram	Principle	Features
YT-5L-type piezoelectric ceramic piezoelectric element [73]		The YT-5L-type piezoelectric ceramic has been utilized as a sensitive element, while a stainless steel 304 thin plate has been employed as a sensitive plate. The electrodes and shielded wire lead into the signal modulation circuit have been fabricated using double-conducting copper foil tape developed by Harbin Institute of Technology Bosheng Precision Company in Heilongjiang, China. The detection unit and seeds, stalks collision test, and measurement of collision signal characteristics have been constructed.	The multivariate fuzzy controller is employed for loss clearance, with the monitoring amount of the loss detection sensor serving as the input to facilitate the automatic adjustment of the parameters of the working parts. This process is capable of achieving an effective reduction in seed-clearing loss with high sensitivity.
Austenitic Stainless Steel No. 304 Array Piezoelectric Crystal Sensor [74,75]		The output port transmits the signal of seed-clearing loss to the microcontroller. Subsequently, the monitoring program carries out the counting process and displays the result on the LCD in real time. This completes the online monitoring of the clearing loss. If the result exceeds the preset limit value, the instrument will trigger an alarm.	The reduction in uncertainty in the information is accompanied by the enhancement of the reliability of the system, as well as the extension of the performance of individual sensors, a phenomenon that is facilitated by redundant and complementary data between sensors.
PVDF Piezoelectric Film Sensors [76]		The analog circuit, with its core composed of the AT89C52 microcontroller and its sensitive element constituted by PVDF piezoelectric film, functions by outputting the signals of entrainment and scavenging loss charge to the microcontroller. There, the microcontroller performs the calculation of the loss rate.	PVDF, a recently developed polymer material, finds application in the domain of weak impact and acceleration measurements due to its high piezoelectric constant, sensitivity, wide frequency response, low acoustic impedance, and aptitude for utilization in harsh environments [77,78]
TS1100 Symmetrical Sensor Structure [79]		The system under consideration comprises three components: a symmetrical structure sensor, a signal conditioning unit, and a monitoring and control unit. It has been demonstrated that compensating for sense disturbance signals and implementing band-pass filtering circuits effectively extracts the loss signal of grain. Ultimately, real-time monitoring and counting are carried out by the microcontroller [80].	In comparison with the asymmetric structure, the monitoring accuracy and reliability of the seed loss signal are significantly enhanced.

.

Furthermore, to ensure uniform distribution of material across the screen during cleaning, New Holland’s CX5000 and CX6000 models have been equipped with the Smart Sieve™ system. This innovation utilizes the principle of variable inclination of the screen, in conjunction with the Opti-Fan™ system of airflow adjustment, to counteract the effects of side slopes. The result is the uniform distribution of material at all inclines, thereby enhancing cleaning efficiency.

4. Worldwide Equipment for Minor Cereal Harvesting

The primary production regions of Chinese minor cereals are predominantly situated in the northern regions of the country. These areas are characterized by poor soil fertility and arid soil conditions, resulting in scattered plots and overall yields that are not particularly high [81,82,83]. These factors have contributed to the relatively slow development of mechanized equipment for the harvesting of minor cereals. However, recent years have seen a surge in experimental research on mechanized harvesting of cereals, buckwheat, oats, and other minor cereal crops by researchers from various countries and research teams from enterprises [84]. On the one hand, the technology of grain and rape combine harvesters has already reached a certain level of maturity, and these harvesters have been adapted to the harvesting of minor cereals. For example, the Xinjiang-2 series self-propelled grain combine harvester, developed by China Harvesting Machinery Company in Henan, China, has improved some components to make it suitable for grain harvesting [85]. The grain combine harvester was modified from the John Deere 1042 grain combine harvester in the U.S.A. However, such machines operated with many ears dropped from the header, high clearing losses, and a high rate of impurity content. Consequently, researchers have also developed models dedicated to minor cereal harvesting, which demonstrate superior performance, such as the 4LZG-2-type grain harvester produced by China Harvesting Machinery Company in Henan, China. The Dongfeng 4LZ-1.5-1548-type grain special harvester, produced by Jilin Machinery and Equipment Company in China, is another example of specialized harvesting equipment that exhibits reduced losses and enhanced harvesting outcomes.

4.1. Small and Medium-Sized Minor Cereals Combine Harvester

As stipulated in the agricultural machinery promotion appraisal syllabus DG-T 014-2019, promulgated by the Ministry of Agriculture and Rural Affairs of China, the rating of large, medium, and small full-feed grain harvesters is determined by their feeding capacity [86]. The precise classification is delineated in

Table 5. Criteria for evaluation of grain harvesters.

Machine Type	Wheel Type	Rated Intake Capacity (a, kg/s)
Large	Wheeled	a ≥ 5
	Tracked	a ≥ 4
Medium	Wheeled	5 > a ≥ 2
	Tracked	4 > a > 1.5
Small	Wheeled	a < 2
	Tracked	a ≤ 1.5

.

To enhance the mechanized harvesting of grains in hilly mountainous regions, reduce the cost of production during the harvest period, and address the challenges posed by the limited harvesting season and severe labor shortage during the harvest season, small and medium-sized grains harvesting machinery around the world have dedicated significant research efforts to the development of a range of small and medium-sized grains harvesting machinery suitable for harvesting operations in hilly mountainous areas. Notable enterprises in this field include Kubota from Osaka, Japan, John Deere from Illinois, the United States, and KS Agrotech Pvt. Ltd. from Sangrur, Punjab, India. These enterprises have developed specialized equipment for harvesting grains in hilly terrain. In China, the 4LZ-2 and 4LZ-2A-type full-feed grain combine harvester models produced by Foton Leiwo Gushen Company in Shandong feed at less than 2 kg/s, while the 4LZB-4GA-type feed of the Foton Leiwo Gushen Company is 4 kg/s. The 4LZG-3.0-type grain combine harvester with a feed capacity of 3.3 kg/s was developed by the Nanjing Agricultural Mechanization Research Institute in Nanjing, China. The following table (

Table 6. Structures and characteristics of typical small and medium-sized combined minor cereal harvesting machines.

Name/Model	Schematic Diagram of Structure	Technical Features
The 4LZG-3.0 Self-Propelled Track Millet Combine Harvester was developed by Xingguang Agricultural Machinery Company in Henan, China		The external dimensions of the machine are as follows: length, 5080 mm; width, 2685 mm; height, 2605 mm. The machine’s weight is 2570 kg. The working width is 2000 mm. The machine’s productivity ranges from 0.23 to 0.45 hectares per hour. The machine’s feeding capacity is 3.3 kg/s, and its minimum ground clearance is 240 mm. It is equipped with a double-drum transverse-axial flow threshing-type grid-type concave plate sieve, a reciprocating double-decker vibrating sieve, and an agricultural centrifugal fan [87].
The 4LZ-2 Self-Propelled Full-Feed Sorghum Combine Harvester was developed by Futian Lovol GuShen Company in Shandong, China		The engine power is 66 kW. The cutting width is 2360 mm. The feeding capacity is 2 kg/s. The productivity is 0.33–0.53 m2/h. The total weight is 3650 kg. The equipment includes eccentric elastic tooth paddle wheels, a wheeled front-drive walking system, and a ripple block-bow tooth combination threshing drum and wind-screening drum [88].
The 4LZB-4GA Self-Propelled Track Full-Feed Combine Harvester was developed by Futian Lovol GuShen Company in Shandong, China		The dimensions of the machine are as follows: length 6080 mm, width 2780 mm, and height 2060 mm. The length of the header is 2300 mm. The weight of the machine is 3490 kg. The feeding volume is 4 kg/s. The engine power is 74 KW. The machine is equipped with a 900-mm diameter cutting knife of the 2nd type, an eccentric elastic tooth-type paddle sheave, and a longitudinal axial flow threshing drum. The minimum ground clearance is 280 mm, and a re-thresher with an impeller-toothed plate is employed to minimize loss.
The W70 Combine Harvester was developed by John Deere Company in Illinois, USA		The machine’s dimensions are as follows: length, 7400 mm; width, 3660 mm; height, 3400 mm. The header width is 3280 mm. The machine weighs 5200 kg. The feeding volume is 3.5 kg/s (wheat). The engine power is 80 KW, and the machine adopts a ripple-type threshing drum, a four-key-type manuscript-by-drawer, a front-drive wheeled walking system, a minimum ground clearance of 440 mm, and a driving tire spacing of 2150 mm.
The 4LZY-1.8 (PRO688Q) Tracked Full-Feed Combine Harvester was developed by Kubota Corporation in Osaka, Japan		The dimensions of the machine are as follows: length 5150 mm, width 2810 mm, and height 2815 mm. The width of the header is 2000 mm. The weight of the machine is 2930 kg. The feeding volume is 2.5 kg/s. The engine is a vertical water-cooled 4-cylinder turbo diesel engine with a power output of 49.2 KW. The detachment part adopts a longitudinal axial-flow type, and the track spacing is 1150 mm. The eccentric paddle-toothed paddle wheel is also noteworthy.

) provides a comprehensive overview of the structural and functional characteristics of the prevailing small and medium-sized minor cereal combine harvesting machinery.

In addition to the five small and medium-sized minor cereal harvesters developed around the world that are mentioned in the table, there are Chinese enterprises such as the Cangxi Agricultural Machinery Manufacturing Company of Sichuan Province, and the Hunan Provincial God’s Hand Machinery Manufacturing Company. The Guangdong Danxia Agricultural Machinery Company, the Chongqing Yingfengmin Machinery Company, and the Shuangfeng Xiangyuan Jinsui Harvester Manufacturing Company have also developed small and medium-sized minor cereal harvesters.

In addition, the research team of Zhao Wuyun from Gansu Agricultural University, through studying the growth and cultivation of small minor cereals in hilly and mountainous areas, adopted the “1+N” design model. One host machine is equipped with a variety of different harvesting attachments. By changing the attachments, efficient and low-loss mechanized harvesting of different minor cereal crops such as millet, buckwheat, and Panicum miliaceum can be achieved. In October 2024, field experiments were conducted in Huining County, Baiyin City, Gansu Province. The results showed that the harvester had good harvesting performance and a low loss rate, and significantly reduced the cost of mechanized harvesting of minor cereals. Figure 7 shows the 4LZ-8.0 millet, buckwheat, and Panicum miliaceum combine harvester developed by Gansu Agricultural University.

4.2. Large Combined Harvester for Minor Cereals

Large mixed-grain combines are wheeled harvesters with a feed rate of more than 5 kg/s and tracked harvesters with a feed rate of more than 4 kg/s. To achieve the required feed rate, the structure of large combines has been adapted. First, large harvesters have a larger cutting width of the cutter bar to harvest more rows at the same time; threshers often use double drums or axial flow drums to handle larger feed volumes; large harvesters have larger cleaning sieves, higher blower power, and higher efficiency; large models may also have wider overpass designs to improve feeding smoothness and efficiency; finally, large harvesters have higher engine power, more complex drive systems, and are more expensive. China is the world’s largest producer of various cereals, and ranks first in the world in terms of cereal area and total production [89]. Data from the China Plantation Information Network (CPIN) show that the provinces of Shanxi, Hebei, and Inner Mongolia account for 68.1% of Chinese grain area [81]. However, most of the small grains are still distributed in hilly areas, with small plots and large slopes, and are dominated by individual family farming and production, and it is difficult to improve the conditions for mechanized farming [90]. Therefore, the development and application of large-scale minor cereal harvesters are relatively small, and the typical models such as Zhongnong Group 4LGZ-4.0Z self-propelled grain harvester, which adopts a four-wheel front drive walking system, design a grain-specific harvesting header to solve the problem of header entanglement, and adopt a double-sided wind screen-type clearing structure, with a feeding volume of 5 kg/s or more, which was tested in field experiments in Shijiazhuang, Hebei Province in September 2019. The test results showed that for the prototype machine with a feeding capacity of 5.1 kg/s, the total loss rate was 4%, the crushing rate was 2%, and the impurity content rate was 2% lower than the national standard requirements [91]. Unlike the grain general-purpose large-scale minor cereal harvester in the application of more, this type of machine only needs to replace the cutting platform and adjust some of the parameters to harvest minor cereal crops; the U.S. John Deere W80/W100/C100/230-grain combine harvester, the CASE IH AXIAL-FLOW 4000 series of grain combines, the Chinese Leiwo GM100 self-propelled wheeled grain combine harvester, the Zoomlion TF220 grain combine harvester, and the Chunyu MC H80 PLUS (G4) multifunctional grain harvester can replace their cutting decks to harvest minor cereals.

4.3. Characteristics of Harvesting Equipment for Minor Cereals in Various Countries

By comparing and analyzing the characteristics of minor cereal harvesting equipment and technologies in China and other countries, the development of minor cereal harvesting equipment worldwide has the following features:

• The development is mainly focused on small and medium-sized minor cereal harvesters. The cultivation of minor cereals is mostly concentrated in regions such as the Loess Plateau, Inner Mongolia Plateau, Yunnan–Guizhou Plateau, and Tibetan Plateau, which are predominantly hilly areas not suitable for large combine harvesters to operate. Therefore, at the current stage, the majority of the minor cereal combine harvesters put into use are of small and medium sizes.
• There are more general-purpose grain harvesters than specialized minor cereal harvesters. The planting area of minor cereals in China accounts for 8% to 10% of the national grain crop sowing area, and the proportion of its output in the total grain output is less than 5%. To save development costs and improve economic efficiency, general-purpose grain harvesters are often used to harvest some minor cereals by replacing the cutterbar and adjusting equipment parameters. At present, there are only a few specialized minor cereal harvesters.
• It is difficult to achieve multi-purpose use of a single machine for minor cereals, resulting in low equipment utilization rates. Minor cereals mainly include millet, Panicum miliaceum, and buckwheat, among others. The shapes of these different crops vary significantly, and the harvesting conditions also differ greatly across regions. At the current stage, the developed minor cereal harvesters can only harvest a single type of crop and are unable to serve multiple purposes with one machine.
• The level of intelligence is low. At present, most of the minor cereal harvesting machinery studied in China is still in the pure mechanical design stage. Currently, some research institutes and enterprises have achieved certain intelligent research results in a few key components, but there are few product applications. There is still a gap to achieve control intelligence, operation automation, and comfortable driving.

5. Issues and Development Suggestions

Despite ongoing efforts in research and development, the mechanized harvesting rate for minor cereals remains low due to several key challenges. Firstly, regional imbalances in mechanization levels, with fragmented farmland in plateau and hilly areas limiting the use of large harvesters, contrast sharply with the flatter terrains of the Northeast and Xinjiang, which have higher mechanization rates. Secondly, small-scale farming practices lead to non-uniformity in planting and harvesting, increasing costs and complicating mechanized operations. Moreover, most harvesters are modified from rice or rapeseed models, resulting in poor applicability and high losses, while specialized harvesters for specific crops like millet have low utilization rates. Additionally, promoted crop varieties exhibit inconsistent characteristics, affecting harvesting conditions and increasing losses. Finally, insufficient investment in research and inadequate promotion of mechanized production further hinder progress, particularly in regions like southwestern China. To address these challenges, future efforts should focus on the following key areas:

To tackle the issue of regional imbalances and fragmented farmland, efforts should be concentrated on accelerating the breeding of crop varieties with traits that enhance mechanized planting and harvesting, such as uniform plant height and maturity. This will help standardize planting practices and improve the compatibility of machinery with the specific conditions of fragmented farmland.

In response to the challenges posed by small-scale farming practices and non-uniformity in planting and harvesting, it is essential to develop low-loss and high-efficiency flexible cutterbars that can address issues like drooping panicles and terrain-induced tilting. This will improve crop separation and reduce losses, thereby simplifying mechanized operations.

To address the limitations of existing harvesters and their poor applicability, there is a need to design dedicated threshing devices tailored to the unique panicle structures of minor cereals, incorporating secondary threshing to reduce losses. This will enhance the efficiency and effectiveness of specialized harvesters.

To improve the situation in hilly and mountainous areas, it is crucial to strengthen guidance and support for mechanized cultivation and harvesting, standardize planting practices, and promote scaled production. This will help overcome the challenges posed by fragmented farmland and small-scale farming.

To counteract the insufficient investment in research and inadequate promotion of mechanized production, the government should enhance policy support for mechanized production, increase research and development investment, and encourage collaboration among stakeholders. This will drive and innovation the adoption of advanced technologies, particularly in regions where progress is currently hindered.

6. Conclusions

• This paper provides a comprehensive and systematic review and analysis of the mechanized harvesting industry for minor cereals, covering the current status, key technologies, advanced equipment, existing problems, and suggestions.
• A comprehensive analysis of the current research status of key technologies for minor cereal combine harvesters in terms of the header, threshing, cleaning, mobility, and intelligentization was conducted.
• A comparative analysis of the characteristics of global minor cereal mechanized harvesting equipment was performed. Existing minor cereal harvesters are mostly assembled from grain harvesters by adjusting certain parameters, resulting in low harvesting efficiency and high loss rates.
• To address the existing problems, such as low efficiency, high losses, and poor adaptability of current equipment, it is proposed that improvements can be made in the selection of suitable minor cereal varieties for mechanical harvesting, flexible headers, and the design of the roll threshing device. The impact of intelligentization technology and equipment modularization on the development of minor cereal mechanized harvesting is emphasized.