Rice direct seeding for bunch planting is a sustainable agricultural production method that reduces production costs, improves rice lodging resistance, and conserves irrigation water in the field. However, there are notable differences in seed treatment between direct seeding on dry land and in paddy fields, which can impact the seeding process’s accuracy. This study employs the numerical simulation methods of computational fluid dynamics (CFDs) and discrete element method (DEM) to examine the motion characteristics of dry and wet rice seeds in a fluid–solid coupled domain and their impact on seeding accuracy. The aim is to guide the optimization of the rice air-suction seed metering device. Rice seeds were divided into dry and wet groups, and their physical properties were measured. Discrete element models of rice seeds were constructed and calibrated using a polyhedral method. The results show that the static friction coefficient between the seed meter and the seed ranged from 0.902 to 0.950, and the thousand-grain weights ranged from 25.89 to 32.42 g, which were higher than those of the dry rice seed, which ranged from 0.774 to 0.839, and from 25.89 to 32.42 g. After calibration, the errors between the simulated dynamic stacking angles of HHZD, HYD, YLYD, HHZW, HYW, and YLYW and the physical–dynamic stacking angles were 0.12%, 0.13%, 0.75%, 0.62%, 0.08%, 0.75%, 0.59%, and 1.24%, respectively, which indicated that the discrete element model for rice was reliable. Additionally, a seeding accuracy test revealed that wet seeds of the same variety had higher missing and single indices, while dry seeds had higher triple and multiple indices. Furthermore, CFD-DEM simulations demonstrated that wet seeds’ normal and tangential forces were more significant than those on dry seeds during the seed-filling process. At 40 rpm, the normal and tangential forces during the seed-filling process of HYW are 37.69 × 10−3 N and 12.47 × 10−3 N, respectively, which are higher than those of HYD (25.18 × 10−3 N and 9.19 × 10−3 N). The action force of suctioned rice seeds was directly proportional to the missing and single indices. The primary factors contributing to the discrepancy in seeding accuracy between dry and wet rice are the thousand-grain weight, the static friction coefficient between the seed meter and the seed, and the action force exerted between the rice seeds. In addition, using a shaped hole structure and optimizing the seed chamber structure can reduce normal and tangential forces and improve seeding accuracy. This study provides a reference for the simulation of rice seed flow-solid coupling and optimization of air-suction seed metering devices.

Compared to traditional manual methods for assessing the cotton verticillium wilt (CVW) hazard level, utilizing deep learning models for foliage segmentation can significantly improve the evaluation accuracy. However, instance segmentation methods for images with complex backgrounds often suffer from low accuracy and delayed segmentation. To address this issue, an improved model, YOLO-VW, with high accuracy, high efficiency, and a light weight, was proposed for CVW hazard level assessment based on the YOLOv10n model. (1) It replaced conventional convolutions with the lightweight GhostConv, reducing the computational time. (2) The STC module based on the Swin Transformer enhanced the expression of foliage and disease spot boundary features, further reducing the model size. (3) It integrated a squeeze-and-excitation (SE) attention mechanism to suppress irrelevant background information. (4) It employed the stochastic gradient descent (SGD) optimizer to enhance the performance and shorten the detection time. The improved CVW severity assessment model was then deployed on a server, and a real-time detection application (APP) for CVW severity assessment was developed based on this model. The results indicated the following. (1) The YOLO-VW model achieved a mean average precision (mAP) of 89.2% and a frame per second (FPS) rate of 157.98 f/s in assessing CVW, representing improvements of 2.4% and 21.37 f/s over the original model, respectively. (2) The YOLO-VW model’s parameters and floating point operations per second (FLOPs) were 1.59 M and 7.8 G, respectively, compressed by 44% and 33.9% compared to the original YOLOv10n model. (3) After deploying the YOLO-VW model on a smartphone, the processing time for each image was 2.42 s, and the evaluation accuracy under various environmental conditions reached 85.5%, representing a 15% improvement compared to the original YOLOv10n model. Based on these findings, YOLO-VW meets the requirements for real-time detection, offering greater robustness, efficiency, and portability in practical applications. This model provides technical support for controlling CVW and developing cotton varieties resistant to verticillium wilt.

The acquisition of rice seeding accuracy information could provide adequate support for the operational status of the rice pneumatic seed metering device and field management in the later stages. However, this task proved difficult due to the high speed of rice seeding and the occurrence of non-single seed seeding. In order to achieve real-time detection of seeding accuracy during the rice pneumatic seed metering device operation, a real-time detection system for the seeding accuracy of the device was designed. This paper introduced the system's main components and working principles in detail and proposed a rice seed accuracy detection algorithm based on the improved YOLOv5n.The algorithm utilised the Faster-Net neural network, replacing the CSPDarknet53 network that served as the backbone of the original algorithm. Additionally, it incorporated the CARAFE operator and introduced the Soft-NMS-CIOU technique, a form of soft non-maximum suppression, along with integrating the CBAM attention mechanism module. These enhancements improved the model's feature extraction capability on rice seed images, enabling real-time detection of small rice seeds in the dark environment within the rice pneumatic seed metering device. This improved accuracy in recognising small rice seed images and reduced the probability of false detections. Through comparative analysis with different algorithms, test results demonstrated that this algorithm exhibited a higher pass rate and faster response time compared to others. A verification test was conducted to evaluate identification accuracy at various seed sucking plate rotational speeds. The detection accuracies were 96 %, 96 %, 98.65 %, 88.8 % and 91 %, respectively, at seed sucking plate rotational speeds of 10, 20, 30, 40, and 50 r/min, with a suction negative pressure of 1.6 kPa. Based on the experimental findings, the algorithm met the requirements for seeding detection and could serve as a foundation for further research into seeding accuracy detection algorithms for rice pneumatic seed metering devices.

The key factor in improving the field distribution and yield of rice is precise seeding of rice seed particles in a hill. In this study, a positive pressure precision seed throwing device was designed to enhance the performance of rice seeding on a hill and address the issue of uneven distribution of rice seed particles in the field using the double cavity pneumatic seed metering device. CFD-DEM (Computational Fluid Dynamics - Discrete Element Method) coupled simulation technology was employed to analyse the seeding in a hill and the motion of rice seed particles. The movement details and state of rice seed particles in the airflow were examined, and the effect of precision transportation under different parameters of the positive pressure precision seed throwing device was investigated. The results indicate that an increase in inlet air velocity leads to greater lateral displacement of rice particles under the same inlet angle. A good performance of seeding on a hill was observed when the inlet air velocity was 3 m/s, the inlet angle was 60 degrees, and the speed of the seed sucking plate was 20 r/min. The simulation results identified the optimal hill diameter as 27.5 mm. Subsequent actual tests conducted under the same conditions yielded an optimal hill diameter of 31.2 mm. The results of the actual test and simulation test were basically consistent. This study successfully enhanced the performance of rice seeding on a hill, meeting the requirements for field seeding on a hill.

为了适应杂交水稻的多样性,以及满足杂交稻精量播种的要求,该研究结合水稻气力式播量可调排种器设计了一种水稻气力式播量可调穴播机.该穴播机采用独立风机为排种器提供气源,根据排种器气压需求,设计了单段式管路与双段式管路,并进行对比试验分析,试验结果表明,双段式管路能更加均匀的分配气压,且双段式管路气压的变异系数小于5％.采用杂交稻五优1179为试验对象,在不同的吸种负压下,进行不同播量的田间试验研究,试验结果表明:当2孔工作时,最佳吸种负压为2.0 kPa,平均播种合格率为:93.35％;当3孔工作时,最佳吸种负压为1.6 kPa,平均播种合格率为:87.21％;当4孔工作时,最佳吸种负压为1.6 kPa,平均播种合格率为:83.73％;当5孔工作时,最佳吸种负压为1.6 kPa,平均播种合格率为:79.86％.该研究分析了影响田间播种的主要影响因素,且由试验可得,该机可满足田间播量可调的需求,为实际的生产应用提供了一定的基础.

In order to improve the single-grain seeding rate of the pneumatic single seed metering device, an airflow seed cleaning device was designed in combination with positive pressure airflow. The influence of the position of the seed cleaning mechanism on the seed cleaning effect is theoretically analyzed and a flow field simulation test analysis of different nozzle structures was carried out by using Fluent software (ANSYS, Inc., Canonsburg, PA, USA). The results of this test show that a nozzle with a Witoszynski curve has good airflow concentration and uniform air pressure distribution. In order to verify the performance of the seed cleaning mechanism, a 0.7 times coated seed (hybrid rice Wuyou 1179) was used as the test material and a quadratic regression test with three levels was carried out with the rotation speed of the seed plate, the negative pressure of the suction chamber, and the positive pressure of the seed cleaning as the test factors. The results showed that when the speed of sucking plate was 30 r/min, the negative pressure of the suction chamber was 1.8 kPa and the positive pressure of the seed cleaning was 0.2 kPa; the seeding effect was at its best and the qualified rate of the seed metering device was the highest at 86.43%, the minimum leakage rate was 3.81%, and the multiple rate was 9.76%. The proposed seed cleaning mechanism effectively improves the accuracy of seeding and provides a certain theoretical basis for the single-grain sowing of hybrid rice.

To adapt to the diversity of hybrid rice and meet its requirements of precision seeding, a rice pneumatic seeder with adjustable seeding rates was designed in this study. The seeder employed an independent vortex pump to provide the air source for the seed metering device. According to the requirements of air flow in the seed metering device, a sub-pipeline and a general pipeline were designed. The performances of the two types of pipelines were verified by the air pressure uniformity tests. The results showed that the sub-pipeline can distribute the air pressure more evenly than the general pipeline. The coefficient of variation of the sub-pipeline pressure was less than 5%. Wuyou 1179 hybrid rice was selected as the experimental object. The field seeding tests were carried out with different negative pressures and different number of groups of sucking holes as experimental factors. The results showed that the average qualified rate of seeding was 93.35% when only 2 groups of sucking holes were working under the seed sucking negative pressure of 2.0 kPa. The average qualified rate of seeding was 87.21% when 3 groups of sucking holes were working under the seed sucking negative pressure of 1.6 kPa. The average qualified rate of seeding was 83.73% when 4 groups of sucking holes were working under the seed sucking negative pressure of 1.6 kPa. The average qualified rate of seeding was 79.86% when 5 groups of sucking holes were working under the seed sucking negative pressure of 1.6 kPa. The main factors affecting the seeding effect were analyzed and the feasibility of a rice pneumatic seeder with adjustable seeding rates was verified by field tests. The research results can provide a basis for its practical production and application. Keywords: agricultural machinery, adjustable seeding rate, seeder, pneumatic, rice, pipeline DOI: 10.25165/j.ijabe.20211404.5658 Citation: Xing H, Wang Z M, Luo X W, Zang Y, He S Y, Xu P, et al. Design and experimental analysis of rice pneumatic seeder with adjustable seeding rate. Int J Agric & Biol Eng, 2021; 14(4): 113–122.

Rice seeding in hill is beneficial to the growth of rice in the field and the increase of rice yield. However, rice seed metering device usually uses multiple rice seeds for sowing, which is difficult to form a hill. To improve the performance of rice seeding in hill, the seed throwing mechanism of the rice pneumatic seed metering device with adjustable seeding rate was study, and the trajectory of seed throwing was analyzed theoretically. The equation of seed throwing trajectory was established. The distribution of sucking holes on the sucking plate was optimized by using asynchronous seed throwing method. The distribution mechanism of seed throwing was studied, and the theoretical trajectory area of seed throwing was established. The actual trajectory area of seed throwing was established by high-speed photography. The theoretical area and actual trajectory area of seed throwing were compared by experiments. The influence factor of errors between the actual and theoretical seed trajectory areas were analyzed. The performance of seed throwing in hill was tested under different positive pressure and different rotational speeds. The optimum qualification rates of different seeding rates were 97.34%, 90.36% and 87.36% respectively. These were 10-17% higher than the original qualification rates of seed throwing. The experimental results showed that the optimized sucking holes on sucking plate could effectively improve the performance of seeding in hill of seed metering device. This study provided a theoretical basis for the seed throwing mechanism of the rice pneumatic seed metering device, and improved the qualification rate of seed throwing.

杂交水稻分蘖能力强,产量高.为满足杂交水稻水田直播需求,该研究以3～5粒/穴为播种目标,设计了一种双腔气力式水稻精量直播机.介绍了双腔气力式水稻精量直播机主要工作部件结构,并对负压风力系统进行选型与设计.以杂交稻甬优4949为试验对象,以吸种负压与直播机前进速度为影响因素进行了田间试验.试验结果表明:当吸种负压为3.2 kPa、直播机前进速度为0.2～0.4 m/s时,10行排种器平均播种合格率(3～5粒/穴占比)为91.04％,0～2粒/穴占比2.23％,大于5粒/穴占比6.73％,各排种器之间的播种合格率变异系数为1.24％,满足杂交稻田间播种作业要求,为水田精量直播提供了参考依据.

HighlightsThe problems of high resistance to seed sucking and the poor stability of seed sucking were solved.A mechanical model was established for seeds in a seed stirring device.The optimum parameters of the seed stirring device were obtained.Seeding precision was improved, providing a reference for the seed sucking process.Abstract. To achieve a goal of precision seeding with 1 to 3 seeds per hill and to solve problems in a pneumatic rice seed metering device, including high resistance to seed sucking, poor stability of seed suction, and low seeding precision, a cylindrical seed stirring device was designed. The design was based on the characteristics of the rice seed flow in the seed suction area. A mechanical model of the rice seed in the seed stirring device was established. The relationships between the seed fluidity and the parameters of the seed stirring device were simulated with EDEM software. The effects of seed fluidity on the seed suction area were analyzed under different seed stirring device parameters. To analyze the influences of different parameters of the seed stirring device on seed stirring and to observe the relationships between different parameters and rice seeds, high-speed photography was used to observe the seed sucking and stirring processes. The super hybrid rice Y-2 You 900 was selected as the test material. The seeding precision was tested at different rotating speeds, negative pressures, and parameters of the seed stirring device. The test results showed that an increase in the diameter and thickness of the seed stirring device was beneficial for increasing the seed absorption rate and reducing the missed seed rate but also increased the rate of multiple-seed sucking and reduced the seeding precision. The optimal parameters of the seed stirring device were a cylinder thickness of 2 mm and a diameter of 5 mm. This study provides a certain reference basis for the seed suction process of a pneumatic seed metering device. Keywords: Agricultural machinery, Precision seeding, Rice sowing, Seed stirring device, Seeder.

[目的]为了改善水稻气力式排种器工作时稻种的重吸附现象,设计了一种垂直于排种盘平面的清种装置.[方法]对水稻气力式排种器工作时稻种的受力与清种装置的工作原理进行了分析,建立了吸种过程中的受力模型.采用超级杂交稻'五丰优615'为试验对象,在有、无清种装置的条件下进行了排种器的精度试验.在吸室负压为4.0 kPa的条件下,进行了清种块厚度和排种盘转速的两因素试验分析.[结果]采用清种装置后,1～3粒/穴的占比由62.02％ 提升至90.00％ 左右,≥4粒/穴的占比由37.98％ 降至5.00％,改进效果较为明显.当清种块厚度为3.5 mm、排种盘转速为15、20和25 r/min时,1、2和3粒/穴的占比分别为95.18％、95.16％ 和95.23％,空穴率分别为2.07％、2.76％ 和4.56％,满足超级杂交稻的田间播种需求.[结论]当吸室负压一定时,降低排种盘转速可以提高清种装置的清种效果,提高排种器的播种精度.本文针对水稻气力式排种器的结构,设计了一种清种装置,有效地清除了排种器重吸附的稻种,为提高水稻气力式排种器的精度提供了依据.

为了满足杂交水稻播种量不同的要求,该文设计了一种水稻播量可调气力式排种器,对其工作原理进行了分析,对关键部件进行了参数设计,该排种器采用多个相互独立的负压流道对吸种精度进行控制.利用ANSYS-FLUENT有限元流体分析软件对负压流道结构的吸孔负压影响规律进行了分析,优选了最佳流道结构.选取超级杂交稻Y-2优900为试验材料,进行了不同播种量下吸室负压、排种盘转速与排种盘吸孔组数对播种精度的影响试验研究,试验结果表明:当吸孔组数为12、吸种负压为1.6 kPa和排种盘转速为20 r/min时,1孔播种达到最佳效果,合格率为82.41％;当吸孔组数为12、吸种负压为1.6 kPa和排种盘转速为40 r/min时,2孔播种达到最佳效果,合格率为96.36％;当吸孔组数为12、吸种负压为1.6 kPa和排种盘转速为20 r/min时,3孔播种达到最佳效果,合格率为92.79％;当吸孔组数为16、吸种负压为1.2 kPa和排种盘转速为20 r/min时,4孔播种达到最佳效果,合格率为91.93％;当吸孔组数为12、吸种负压为1.6 kPa和排种盘转速为30 r/min时,5孔播种达到最佳效果,合格率为87.88％.说明水稻气力式播量可调排种器可满足杂交稻在采用直播式时不同播量的要求,相比于原有的排种器更佳适应水稻的多样性.该研究可为水稻机械化穴直播技术提供了参考.

As a simple and efficient rice planting technology, the precision hill-drop drilling could reach higher yield and better economic benefit in suitable areas. In China, the mechanical direct seeding area has a steady growth in recent years. Great progress has been made in studying on the pneumatic metering device, but the type-hole metering device is still the most widely used on the precision hill-drop drilling machine. The metering device is the core part of the direct seeding machine, and the stability of the seed filling process is an important link to ensure the performance of the seeding. The filling chamber is the most important area for seed-filling process. In this research, we studied the combined hole-type metering device developed by South China Agricultural University. The hole-type roll includes hole-type shell, hole-type roller and adjusting mechanism. A complete hole-type is comprised by the label through holes which are uniformly distributed on the hole-type shell and the small/big type-hole which are uniformly distributed on hole-type roller. The combined hole-type metering device can meet the sowing rate requirement of both conventional rice and hybrid rice simultaneously and it can be most wildly used on the precision rice hill-drop drilling machine. The key parameters of seed-filling initial angle and structure of double seed-filling chamber would affect the seed fluidity and seed-filling stability. In order to study the effect of filling chamber structure on seed-filling performance of combined type-hole metering device, theoretical calculation and experimental verification of seed-filling initial angle, parameters of seed flow adjusting device were carried out. The results of theoretical calculation and the single factor test with the seed-filling initial angle showed that the seed-filling initial angle of combined type-hole metering device was -40°. Using the type of type-hole, the seed-filling initial angle and the working speed of the metering device as variables, the results of the multi-factor test showed that the optimum seed-filling initial angle was -20°. Compared with -10° and 0, seed-filling initial angle at -20° made smaller differences in the average seeds number per hill and the coefficient of variation with different working speed, while there was no significant (P＞ 0.05) difference in the average seeds number per hill and the coefficient of variation among -20°, -30° and -40°. Without affecting the seed-filling performance of metering device, the smaller seed-filling initial angle, the larger contact area between seeds and combined type-hole roll, and in theory, the abrasion of type-hole roll would be accelerated and the breakage of the seeds would be increased. Therefore, it was most reasonable to take the seed-filling initial angle for -20°. The function of seed flow adjusting device was used to regulate the seeds flow from the first filling chamber to the second seed filling chamber, and it changed the position of seed-filling terminate angle to achieve the purpose of regulating the seeding rate. The best distance between the restriction mechanism and the seed metering wheel was 40 mm, which solved the problem that seeds were flung out by the cleaning brush. Using the type of type-hole, the variable of seeds, the position of adjusting plate and the working speed of the seed metering device as variables, the results of the multi-factor test showed that the distance between the regulating seed plate and the type-hole roll can be adjusted within the range of 0-22 mm, and further regulation of seeding rate could be achieved for different types of type-hole and varieties of rice seeds. The design of each parameter was reasonable. In general, seed-filling performance of metering device was improved in this study and the results could enrich our knowledge of the working principle of type-hole metering device.

To meet the requirement of the precision direct-seeding for hybrid rice, this study aimed to design a hill-drop pneumatic central cylinder direct-seeding machine to sow ten rows at a time. A series of orthogonal experiments were conducted to investigate the performance of the cylinder seeder. The influences of the hole diameters, degree of vacuum, and rotational speed of the cylinder were tested on JPS-12 computer-vision seeding test platform, and the rotational speed of 10-50 r/min, diameter of 135 mm and a negative pressure of 1.0-2.0 kPa were employed. Test results showed that the optimal parameter combination was a vacuum of 2.0 kPa and a hole diameter of 2.0 mm (straight hole), with a rotational speed of 30 r/min. The probability of (2±1) seeds in each hole was 95.3%, while the probability of seed-missing hole was 2.0%. A series of field experiments were then conducted to test the seeder performance according to China National Standard Test Methods, and the field test results showed that for the hill-drop pneumatic central cylinder direct-seeding machine, the probability of (2±1) seeds in each hill was 91.6%, while the probability of seed-missing hill was 2.7%. The yield data showed that the average effective panicle had 231.25 ears, the average seed setting rate was 9.92%, the average 1000-grain weight was 22.45 g, and the average yield was 7107.9 kg/hm2 that was 26.14% higher than the average yield of rice (5634.9 kg/hm2) of Guangdong Province in 2016. The results showed that the hill-drop pneumatic central cylinder direct-seeding machine for hybrid rice could be applied in practical precision rice seeding. Keywords: direct-seeding machine, hybrid rice, precision rice seeder, pneumatic cylinder, platform test, field test DOI: 10.25165/j.ijabe.20181106.4175 Citation: Wang B L, Luo X W, Wang Z M, Zheng L, Zhang M H, Dai Y Z, et al. Design and field evaluation of hill-drop pneumatic central cylinder direct-seeding machine for hybrid rice. Int J Agric & Biol Eng, 2018; 11(6): 33–40.

Mechanized rice direct seeding is a cost-effective and efficient approach for rice cultivation. Recently, the use of rice direct seeding has been increasing rapidly owing to rural labour shortages and continuous increases in agricultural production costs. This article reviews the research and application progress of mechanized rice direct seeding including direct seeding technologies, precision rice seeding, precision rice seed-metering devices, key supporting agronomy technologies for mechanized rice direct seeding. South China Agricultural University developed precision rice hill-drop drilling (PRHDD) with synchronous furrowing and ridging technology and series machines for paddy that affords remarkable advantages in terms of saving time and labour, higher yield, and higher efficiency. In this approach, pre-germinated seeds are uniformly hill-dropped in the expected positions in puddled soil. It significantly improved the crop growth population and effectively solved the problems of high frequency of disease and pests caused by the irregular distribution of rice seeds with manual broadcasting, and generally reduces seed usage and increases the yield. Therefore, this technology has broad application prospects and great potential for promoting the development of mechanized rice direct seeding in China. Keywords: rice, precision rice seeder, hill-drop drilling for paddy rice, mechanical direct seeding DOI: 10.25165/j.ijabe.20181103.4249 Citation: Zhang M H, Wang Z M, Luo X W, Zang Y, Yang W W, Xing H, et al. Review of precision rice hill-drop drilling technology and machine for paddy. Int J Agric & Biol Eng, 2018; 11(3): 1–11.

To address the clogging of the rice seed metering device after a long period of operation without affecting the precision of normal seeding, an active seed throwing and cleaning unit was designed based on the fact that magnets of the same pole were mutually exclusive. The working principle of the two devices was analysed theoretically, and a mechanical model was created according to the relationship between the repulsion forces of magnets and the spring forces of springs. The super hybrid rice Y-2 You 900 with 22.5% moisture content (wet basis) was used as the test object. The whole factor experiments were carried out under different negative pressures, rotational speeds of the suction plates, and lengths of probes. The results indicated that under any test conditions, the active seed throwing and cleaning unit worked normally. The results of high-speed photography showed that the rate of seed cleaning was 100%. The results also showed that the optimal negative pressure was 0.8 kPa. The probability of 1-3 seeds per hill for the seed metering device was approximately 95% under the optimal negative pressure. The optimal length of the probe was found to be 2 mm. The average qualified rate of hill space was 96.04% under the optimal length of probe, the longer the length of the probe, the lower the qualified rate of hill space. It also showed that an active seed throwing and cleaning unit could effectively avoid the hole clogging caused by the long-term operation and had no influence on the normal operation of the pneumatic rice seed metering device. The active seed throwing and cleaning unit improved the stability of the seed metering device, and the research provided a reference for the optimal design of seed throwing and cleaning structures of the pneumatic rice seed metering device. Keywords: agricultural machinery, seed metering device, seed cleaning, anti-clogging, pneumatic seed metering, precision seeder DOI: 10.25165/j.ijabe.20181102.3844 Citation: Xing H, Wang Z M, Luo X W, Zang Y, Yang W W, Zhang M H, et al. Design of an active seed throwing and cleaning unit for pneumatic rice seed metering device. Int J Agric & Biol Eng, 2018; 11(2): 62–69.

Rice is the staple food for more than half of the global population, and the rice production, especially planting, needs a lot of labor force, material and financial resources. At present, the rice mechanized planting level is low in China. According to statistics, the mechanization level of rice planting in China was only 44.45% in 2015. The main ways of planting are artificial seeding and transplanting. The mechanization of rice direct seeding technology mainly includes mechanical seeding, mechanical drilling, and hill-direct-seeding. Compared to mechanical transplanting, mechanical direct seeding can avoid the process of raising rice seedlings, reduce the input of prophase cost, and does not affect yield. It is expected to be the developing trend in mechanized rice planting in the future. Normally, it is difficult to control the precision of mechanical sowing and mechanical drilling. This leads to uneven seedling distribution and affects the growth and field management of rice. In recent years, due to the increase of labor cost, the cost of rice planting has also increased. It is imperative to develop the mechanized planting of rice. The mechanization of rice direct seeding can eliminate rice seedlings process and save the labor and material consumption. Super hybrid rice has stronger tillering ability than ordinary hybrid rice. By using direct seeding technology, the high yield population structure can be formed with only 1-3 seeds per hill. The pneumatic rice precision direct seeding technique is a combination of machinery and air flow. This technique has the advantages of high seeding precision, low seed damage rate, and strong adaptability and can satisfy the seeding demands of many kinds of seeds. However, existing pneumatic seed metering devices are mainly for soybean, corn, wheat, rape and other crops. Seed metering devices have been widely used in actual production, and theoretical research is also relatively mature. In this study, the relationship between emergence rate in the field and seeding precision are studied with the pneumatic rice direct seeder seeding super hybrid rice. The relation formula between the germination rate of rice seed and the precision of seeding was established. The field experiments were conducted using pneumatic rice seeder with 10 seed metering devices. 3 kinds of super hybrid rice, which named "Y-2 You", "Chao you 1000" and "Wu feng you 615" respectively, were selected as the research objects. The tests of germination rate in the laboratory and the precision of seeding in the field were carried out. The germination rate was 94%, 91% and 92%, respectively. The seeding qualified rate (the probabilities of 1-3 seeds per hill) was 94.98%, 95.07% and 95.21%, respectively. The probability of empty hill was 1.78%, 2.03% and 1.95%, respectively. The relation formula established in this study was used to calculate theoretical seedling survival rate. The theoretical seedling survival rate were 96.85%, 95.79% and 96.07%, respectively. The actual seedling survival rate in the field were 94.22%, 93.94% and 93.76%, respectively, which were lower than those calculated by theoretical calculation. The main factors that affect the seedling survival rate in the field were analysed. In order to improve the seedling survival rate in the field, 1) the precision of seeder should be further improved, the probability of empty hill and the probabilities of 1 seed per hill should be reduced, and the probabilities of 2 seeds per hill in the agricultural machinery should be increased, 2) the germination rate of rice should be further improved in the agronomy. The results of this study provided a basis for the application of the pneumatic seed metering technology to the precision direct seeding of super hybrid rice.

In order to meet the requirement of field direct seeding for super hybrid rice: 1-3 seeds per hill, a pneumatic rice direct-seeder with six seeding metering devices was designed. Transmission system of pneumatic rice direct-seeder and seed metering device were analyzed in this study. And the pipeline structure and vortex pump were designed and selected. The pressure distribution of the pipeline was tested. The pressure value of each sub-pipeline under the conditions of different main pipeline pressure value was obtained and the reasons for pressure loss were analyzed. The results showed that the variation coefficient between sub-pipelines was less than 5%. The pipeline pressure could be evenly distributed. Further, the field experiments were carried out on super hybrid rice Peizataifeng using two-factor testing, by which the effects of different negative pressure and different forward speed (namely, rotational speed of suction plate) for seeding precision were studied. It found that: (1) the optimal negative pressure was 2 kPa; (2) under the optimal negative pressure, the probabilities of 1-3 seeds per hill for the direct-seeder were 93.41%, 95.47% and 97.50%, respectively, when the forward speed of the direct-seeded was high, medium and low speed; (3) the probability of empty hole was less than 2%, which satisfied the field direct seeding requirements of super hybrid rice. Additionally, hill spacing was measured, and the factors affecting the hill spacing were analyzed. The results showed that the fluctuation of hill spacing in the small range will not affect the seeding effect. In this study, a new type of pneumatic rice direct-seeder was designed. The main working components were tested and analyzed. The best parameters of field work were obtained. It provides the basis for the field application of the pneumatic rice precision seeder. Keywords: agricultural machinery, rice, pneumatic rice direct-seeder, field experiment, pipeline DOI: 10.25165/j.ijabe.20171006.3142 Citation: Xing H, Wang Z M, Luo X W, Cao X M, Liu C B, Zang Y. General structure design and field experiment of pneumatic rice direct-seeder. Int J Agric & Biol Eng, 2017; 10(6): 31–42.

Aiming at the requirements of high speed and large sowing quantity for rice direct seeding, a kind of rice pneumatic centralized seed distributor, including outer cover, inner cover, metering disc, gasket, mounting holes, distribution port, conveying pipe, was designed based on rice pneumatic centralized drilling machine. The distribution mechanism of pneumatic centralized seed distributor was studied according to the adaptability, working speed and seeding quantity adjustment of the drilling machine; the adaptability, uniformity and stability of pneumatic centralized seed distributor were analyzed; the computational fluid dynamics (CFD) simulation with Solidworks Flow software was carried out according to the physical characteristics of rice seeds; the distribution of velocity flow field of the seed distributors with different structure was compared, which contained 3 groups of comparative analysis: Factor 1 was for the internal structure of the conveying pipe, including the corrugated straight pipe and straight pipe without ripple, in which the spreader tube length and distribution port number were the same; Factor 2 was for the length of spreader tube, with 2 lengths of 1.5 and 2.8 m, in which the internal structure of conveying pipe and distribution port number were the same; Factor 3 was for the distribution port number, and one was 10 and the other was 20, in which the internal structure of conveying pipe and spreader tube length were the same. The optimal equal amount flow field (EF) was obtained, whose structure was the central symmetric body, with the velocity and pressure magnitude being equal for each point on the circumference with equal radius; the changes of air velocity flow field were consistent from the beginning to the end, the flow line and the track were coincident, and the seed distributor design parameters were obtained; the seed distributor contained the EF structure, the transportation structure and the spreading structure. And the EF structure was divided into 3 parts: EF1 (the horizontal part of flow field of the cover), EF2 (the circular part of flow field of the cover), and EF3 (the vertical part of flow field of the cover), which were for gathering seeds, dividing seeds and sending seeds, respectively. The structure of the outer cover was optimized through the theoretical analysis and fluid simulation, the velocity magnitude and the dispersion of equal amount flow field were compared, the flow line of EF velocity field was simulated, the proper air source was selected, a seed distributor with homogeneous mixture for air and seeds was designed, and the distribution uniformity and stability of drilling machine were improved. Platform experiment of seed distributor was carried out, and the experimental results were in accord with the CFD simulation analysis. The coefficients of variation of the seeding quantity between rows and intra-row for the 10-row seed distributor, which had the same spreader tubes and corrugated pipe for each row, were 3.58% and 4.55% respectively, and that for the 20-row seed distributor, which had the same spreader tubes and corrugated pipe for each row, were 3.91% and 5.04% respectively, which could meet the requirements of different drilling machines. The CFD and experiment results show that the adding of corrugated structure in the straight pipe can help the rice seeds gathering in the center of the pipe; the length of spreader tubes will influence the seed distribution effect, and therefore especially the intra-row stability, and the length of the seeding pipe should be as uniform as possible; the internal structure of the pipe affects the distribution of the velocity flow; the equidistant circular arc structure formed by the inner and outer covers and the corrugated structure in the conveying pipe are beneficial to the formation of the air and seeds mixed equal amount flow field, which makes the seeding uniformity better.