Haitao JIAO Jingzhe CHEN Junjie ZHANG Haiyan WU Xiaohe LI Xingmao YUAN Fazhi PENG Xiaohui HUANG Zhijie YANG Xiqun ZHANG
Abstract Based on the analysis of the present application of millet mechanization planting machines， we summarized the basic situation of millet mechanization planting machines at present stage to improve of planting efficiency and develop mechanization， and made suggestions on millet sowing mechanization.
Key words Millet; Agricultural machinery; Sowing; Development trends; Suggestion
Millet is a traditional planting crop in China， as well as one of the important food crops in China. Millet planting areas in China are mainly concentrated in arid and semi-arid hilly areas， with many planting patterns[1]. The research of mechanized millet production started relatively late. Compared with other bulk food crops， the development of mechanized millet production technology is backward， and due to the complex topography of the planting area， there are fewer special machines suitable for millet production. At present， most of the existing machines are transformed from rice and wheat machines， and the application area is narrow. Based on this， we systematically summarized current research progress of mechanized millet production in China， and proposed the development direction of millet mechanization in the future in view of the current situation and characteristics of millet machine research and development.
Research Progress of Millet Seeding Mechanization
Millet is a traditional crop in China with a planting area ranking first in the world[2]. The main producing areas are mostly concentrated in the arid and semi-arid hilly areas with underdeveloped economy and relatively backward technology， and there are various planting methods. Compared with wheat， corn and rice， millet planting areas in China are mostly hilly areas， with smaller planting areas and less demand for machinery. The research on production mechanization started late， and the development is lagging behind and has been at a low level. With the improvement of people"s living standards and the improvement of the awareness of the nutritional value of millet， the demand for millet has increased sharply in recent years， and there is an urgent need to develop mechanized millet production. Therefore， research institutes in northeast China， Shanxi， Hebei， Inner Mongolia and other regions have carried out research on millet production machines to varying degrees. The Hebei Agricultural Mechanization Research Institute has successfully developed the 2BF series of small-grain crop planters. The machines have a simple structure and adopt a small seed metering device， which can make the seeding rate uniform and accurate and the seeding depth consistent. They are suitable for precision thinning-free planting of small-grain crops such as millet and broomcorn in plains or hilly areas， and can achieve less thinning， no thinning. The millet film side furrow planter successfully developed by the millet innovation team of Shanxi Agricultural University can effectively use the rainwater collecting effect produced by the formation of micro ridges after film mulching on the cultivated land and make full use of natural precipitation to provide water during the germination and growth period after seeding， greatly improving the survival rate of millet in mountainous and hilly areas.
Research Progress of Seeding Equipment
In view of the agronomic characteristics of millet and other small-grain grains， the key to millet planting is that small-scale sowing， uniform spacing and consistent sowing depth can save a lot of seeds， reduce thinning labor， and ensure stable and high grain yield. Studies have shown that there are five types of planting machines in actual production， including precision drill seeders， precision hill planters， nail planters， air suction planters and spoon planters[3-8]. From the perspective of planting method， they can be divided into conventional flat seeder， ridge seeder， and film side seeder.
The precision drill seeders are composed of a frame， a seed box， a seed metering mechanism， a soil covering device and pressing wheels， and each row is equipped with a single profiling mechanism with consistent seeding depth. The sowing rate of the machines is accurate and adjustable. The straight trough wheels are changed to the oblique trough wheels， so that seeding is even and accurate， and the seeding rate is accurate and adjustable. The machines can achieve no thinning or less thinning， and both the cultivated land and the no tillage land can be sowed. The structure of the precision hill planters is similar to drill planters. They adopt a designed socket-type seed metering device and are designed with no seed scrapers， and have the advantages of no seed damage， accurate hole spacing， and adjustable hole number. The precision hill planters are free of thinning， which greatly reduces the labor intensity; and the single-group profiling design makes the seeding depth stable. The nail planters changed from the traditional gravity filling to rotating power taking the seed. The seeding component is a general mode， with a large seeding mode and a small seeding mode， the switching of which adopts a lock button design. The machine can also sow millet， sorghum， wheat and other crops. The air suction planters adopt negative pressure suction and single seed precision seeding， which can significantly reduce the missed seeding rate and reseeding rate. They have the advantages of strong adaptability to seed size， no damage the seeds， and a high plant spacing qualification rate. They greatly improve the efficiency of planting operations. Film-covering planters are widely used in areas with poor moisture conditions， and are divided into two types of seeding on the film and aside the film. Film-covering seeding can enhance the water supply capacity of the soil， promote the transpiration and evapotranspiration of crops， and make efficient use of limited water. The film-covering planters achieve the effects of water saving and moisture preservation， neat seedling emergence， and high reliability.
Development Trend of Millet Seeding Mechanization
China"s economic development has entered a new normal. Understanding the new normal， adapting to the new normal and leading the new normal are the general logic of economic development at present and in the future. Under the new normal， we should understand and clarify the connotation and extension of modern agricultural development， deepen innovation， seek benefits from land， increase farmers" income， and accelerate and promote the development of the current millet industry. In view of the problems of millet seeding operations， we can consider the integration of agricultural machinery and agronomy， and establish a technical system of millet seeding mechanization based on method innovation， technological breakthroughs， and equipment research and development.
Precision seeding
Selected seeds are the foundation
The quality of seeds not only affects the yield of crops， but also affects the quality of crops. After removing mixed seeds of different crops or varieties， as well as seeds that are not full， moth-eaten or deteriorated， selecting full seeds for sowing can not only reduce the amount of sowing， but also ensure that the seeds germinate and emerge neatly and strongly. The selected seeds tend to have strong growth vigor and stress resistance and generally have rapid and neat emergence， high seedling rate， high yield potential， high product quality， and high economic benefits. Improving the purity and neatness of seeds to ensure the germination rate and seed vigor of seeds， is an important guarantee for realizing precise planting with machinery.
Precision seeder is a tool to achieve precision seeding
At present， the widely used small seed metering devices in the market include socket type， chute wheel type， spoon type and spike-tooth type seed metering devices， etc.， all of which have some shortcomings. For example， the socket-type seed metering device can easily cause seed jamming and uneven number of seeds， resulting in low emergence rate and irregular emergence. Therefore， in the research process， we should pay attention to improving and optimizing the design of the seeding wheel structure and screening and optimizing the materials of the brush and the seed belt. Furthermore， attention should be paid to mold processing to ensure the production process of the socket.
Work standardization
Mechanized precision seeding standards should be formulated to achieve precision seeding. On the basis of a large amount of experimental data， we summarized 6 accurate standardized indicators， which are single-grain rate≥85%， empty hole rate<5%， injury rate≤1.5%， consistent seeding depth with error≤1 cm， consistent plant spacing with a qualification rate≥80%， and the deviation of the seeds from left to right≤4 cm. The determination of these indicators laid a foundation for the realization of mechanization of cultivating， weeding and spraying.
Patterned planting
China has a vast territory， and different regions have different climates， farming conditions， soil characteristics， annual accumulated temperature and moisture content during sowing periods， as well as different cultivation systems and planting methods. When developing mechanized millet machinery， we must follow the principle of adapting measures to local conditions， fully integrate agricultural machinery and agronomy， and select and design matching regional agricultural machinery equipment based on the cultivation mode.
Central and southern plains of North China
The land in this area is flat， and the moisture during planting can be supplemented by pumped wells and canal irrigation. The moisture conditions are easy to control. Rotary tillage and land preparation should be carried out before planting. The farming mode is rotary tillage-suppression-flat drill seeding or ridge seeding， and the corresponding supporting equipment is rotary tiller-roller-drill seeder or ridge seeder.
Northwest hills
The terrain in this area is undulating. It has relatively soft soil with soil moisture difficult to maintain， limited irrigation conditions， and the spring is windy and sandy. Seeding is often carried out when the soil is wet， and the water needed for crop growth in the production management process mostly depends on natural precipitation. Therefore， it is advisable to adopt film mulching for sowing. The farming mode is rotary tillage-suppression-half （full） film mulching hole sowing， and the corresponding supporting equipment is rotary tiller-roller-film mulching machine.
Northeast great plains
The fertile soil in this area is highly viscous， so large-scale traction planters are often used for planting， and the no-tillage planting mode of flat planting combined with mid-term weeding and ridging is adopted. At present， small light no-tillage planters have appeared in western Liaoning. The cultivation mode is deep loosening in autumn-rotation with spring corn-no-tillage sowing， or straw crushing-rotation with summer wheat-no-tillage sowing. The corresponding supporting equipment is subsoiler-no-tillage machine， or straw returning machine （crushing with harvester）-no-tillage machine.
Machine intelligence
As an important part of the realization of modern agriculture， the informatization and intelligence of agricultural machinery is mainly embodied in introducing satellite positioning and navigation systems to improve land utilization， introducing mechanical， electrical， gas， and liquid integrated technology to reduce labor intensity and simplify operations， and introducing a sensor feedback system to monitor the seeding quality in real time[9-11].
Installing tractors with a navigation driving system
The system mainly includes a high-precision angular transducer at the steering position of the tractor"s front wheel， a radio antenna installed in the center of the bracket， and an electric steering wheel composed of a driving motor， a spline sleeve， a fixed bracket and a special steering wheel. The navigation accuracy reaches ±2.5 cm. It is an effective solution to solve the problem of indirect broadcast and inaccurate connection， and provides technical support for maintaining a high degree of consistency in subsequent spraying， fertilizing， and harvesting operations. Meanwhile， precise spacing is ensured， and the rates of heavy tillage and missed tillage are reduced.
Seeding operation information monitoring
Seeding operation information monitoring is an important part of modern precision seeders. It can effectively monitor the seeding link in real time， and can send out an alarm signal in time when a failure occurs. When a machine is planting， it is impossible to directly monitor the quality of the operation by human audiovisual alone， such as blockage during the planting operation， abnormal seeding amount， transmission failure of the seeder， etc.， all of which affect the normal seeding process， resulting in uneven emergence， especially for the large-scale wide-width precision seeders which have high operating speed and wide spreading width. Once the above phenomena occur， they will cause a large area of missed seeding， which will inevitably cause serious losses in agricultural production.
According to the existing seeding monitoring system on the market， a seeding monitoring system can be installed on air suction precision seeders to monitor the seeder"s seeding rate， seeding speed， seeding interval， seeding area， single seeding rate， reseeding rate， and missed seeding rate. The seeding monitoring system is composed of sensors， photoelectric conversion circuit， alarm control and signal display devices. It can monitor the working status of each seed metering device in time， and can correct the seeding situation in time by controlling the compensation device， including missed seeding， seeder metering amount， seeding speed performance parameters， etc. Meanwhile， the original mechanical ground-wheel drive seeding is changed to motor-controlled drive seeding， which， combined with the satellite navigation system， can ensure stable and accurate broadcast volume per unit area through the pre-set data regardless of the speed of the tractor.
Speeding up the weak production mechanization in hilly areas
The planting area of millet in the hilly area of China is relatively large， with the characteristics of small plot area and sporadic distribution. Most of these areas are relatively backward in economy and technology， and do not have irrigation conditions. Modern large-scale agricultural machinery is difficult to enter the ground. To speed up the development of special machines in hilly areas， the focus and direction of improving machine tools for hilly areas special machines for hilly areas are taking small and medium-sized micro machines as the main research object and learning from different crop machine models. It is necessary to increase the research and development and promotion of universal models to achieve the purposes of one machine for multiple purposes， saving cost， and improving efficiency， so as to make up for the mechanical shortcomings of the weak production links of millet in the hilly area.
Suggestions for the Development of Millet and Sorghum Seeding Mechanization
Policy guidance and financial support
For a long time， there has been little research and development of equipment suitable for planting and harvesting millet. Policy and financial assistance should be strengthened， focusing on special support and organizing scientific research units to connect with production enterprises. In view of the key and difficult problems in the research and development， we should carry out scientific and technological research， carry out active and effective cooperation， develop suitable machinery specifically for millet seeding， and realize the mechanization of the whole process of millet production from seeding to harvesting.
Integration of agricultural machinery and agronomy
Agricultural machinery and agronomy are organically integrated， agricultural machinery serves agronomy， and agronomy provides a basis for agricultural machinery. According to different planting areas， standardized cultivation techniques should be formulated. From soil preparation before sowing， sowing to mid-term field weeding and spraying， and finally to harvesting， a set of scientific and systematic techniques can be developed， and on this basis， corresponding agricultural machinery can be provided， so as to improve the adaptability of agricultural machinery and agronomy and maximize the advantages of mechanization.
Establishment of a demonstration base for the integration of agricultural machinery and agronomy
After the initial development of millet industry mechanization， it was concluded that the market has an urgent demand for machinery. This requires us to rigorously screen， classify and formulate usage specifications for the more mature agricultural machinery used in the millet production process， and then promote the application. It is necessary to optimize and improve problems existing in large-scale application of machinery， accelerate the pace of research， and apply mature information integration technology to agricultural machinery equipment as soon as possible to improve the level of intelligence of existing machinery. A demonstration base can be established for the innovation of agricultural machinery and agronomy integration to improve the influence of the supporting technology and machinery.
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