Rice is one of the most significant crops in the world. Enough fertilizer supplied in the different growing period is necessary for the growth and yield of rice. Manual spreading is still the main way of paddy topdressing in China, leading to the inefficient and uneven application. A topdressing machine can be expected to reduce the labor intensity for the high productivity. Among them, the large spreading distance can be required for the mechanical spreading of fertilizer, in order to reduce the running times of the machine in paddy fields. Furthermore, the broken rate is the main influencing factor on the broadcasting distance. In this study, an experimental centrifugal disc fertilizer broadcaster with a guiding chute was designed for the parameter optimization of the machine, in order to increase the spreading range with the less breakage rate of the fertilizer. The broadcaster consisted of a revolving disc with the guiding blades, a feeding part, and a guiding chute. The spreading distance increased to combine the action of centrifugal force and airflow speed. The kinetic analysis of fertilizer grains was carried out to establish a functional relationship between spreading distance and fertilizer particle velocity. The structure and motion parameters of the device were determined, according to the models. The speed of the disc was determined as 850 r/min, the length of the guiding blade as 160 mm, and the distance between the feeding tube and the center of the disc as 90 mm. The fertilizer spreading was simulated using EDEM software. A systematic investigation was conducted to reveal the influence of structural parameters of fertilizer applicator guiding blade and the location of the chute on the initial speed of fertilizer particles. The guiding blade of the disc was determined to be the radial type. The internal airflow field of the fertilizer broadcaster was simulated using FLUENT, in order to clarify the influence of the fertilizer spreader guide tube on the fertilizer particle speed off the guiding chute. The structural parameters of the guide chute were optimized to be 200 mm of the length, 60 mm of the height, and 91.38° of the slope angle of guiding chute. The angle between the feeding tube and guiding chute was 53.75°. The fertilizer particles shared the higher speed at the leaving the guiding chute. The orthogonal experiment of four factors with three levels was conducted to evaluate the effects of blade number, blade form, blade height, and disc-chamber gap on the spreading distance and breakage rate of fertilizer grains. The optimization demonstrated that the distance was 16.95 m, and the fertilizer broken rate was 26.32%, which was 28.2 % lower than that of ordinary fertilizer broadcaster. As such, the fertilizer spreading distance increased by 5 m at the number of blades was 4, the blade type was radial, the height was 15 mm, and the disc-chamber gap was 25 mm. The finding can provide a strong reference for the development of fertilizer application device.

Drought has seriously threatened the normal sowing and seed germination of dryland crops, such as corn and cotton. The fluid seeding can suspend the seeds in a mixture, named as seed-liquid of water and high absorbent polymer (HSP), which can absorb water when high in moisture and slowly release water when lacking. A favorable condition can then provide for the germination and emergence of the crop. The seed damage rate can be reduced for high yield, due to the drought resistance, water conservation, and high emergence rate. It is often required for the uniform distribution of the seeds in the liquid for the fluid seeding quality. Pneumatic agitation can be utilized to generate the flow field for the suspension of the seed. However, the flow field can be confined to the structure of the seed-liquid tank. In this study, four seed-liquid tanks were designed to develop the pneumatic-agitation fluid seeder, including the shapes-square (SQ), triangular type (TRA), quasi wedge (QW), and quasi wedge-arc (QWA). The air was then supplied through the air inlet at the bottom of the seed-liquid tank during operation. A model was also established to determine the relationship between the air consumption for the pneumatic agitation and the structural parameters of the tank. CFD simulation was finally carried out to explore the effect of the vertical section shape of the seed-liquid tank on the flow field of the seed-liquid under various air inlet speeds. The results show that the SQ seed-liquid tank shared the dead space in the circulation, leading to the seed deposition; In the TRA seed-liquid tank, an overall circulation failed to the uniform distribution of seeds, leading to the unstable seed-liquid flow field in the middle and lower parts of the tank; The QW seed-liquid tank shared the multiple small vortices on the flow field of the seed liquid; And the QWA seed-liquid tank exhibited an optimal performance at all air inlet speeds, in terms of the seed-liquid circulation patterns, flow field stability, and the less circulation dead space; Once the inlet air speed was constant, the maximum and minimum ratio of the seed-liquid flow speed varied in a range of 0.04, indicating the minimal fluctuations and optimal stability in the flow speed. An experiment was conducted on the QWA seed-liquid tank to verify the simulation. The stability of the seed-liquid flow field was optimal at the inlet air speed of 4 m/s. There was a relative error of 9.30% between the simulated and the tested flow speed at the ideal area of the seed outlet in the seed-liquid tank. The gas-liquid flow model was simplified to verify the reliability. The pneumatic agitation test was conducted at varying rates of air flow. The theoretical calculations were verified to observe the distribution of the seeds in the seed-liquid tank. The seed deposition decreased at an inlet air flow rate of 1.5 and 2.0 m³/h, and then the seed was distributed relatively uniformly in the liquid, and the corresponding air consumption was 6.67×10^-3 and 8.89×10^-3 m³/h, which was consistent with the predicted value. The finding can provide a strong reference for designing the seed-liquid tanks during fluid seeding.

Topdressing has been widely used to supplement the basic fertilizer in the middle and later growing stages of rice paddy fields. Broadcasting is one of the fertilizer applications to meet the nutritional needs of rice. The commonly used broadcasted fertilizer may flow with the surface water in rice production, resulting in environmental pollution, fertilizer loss and a low utilization rate. And a furrow opener of the most deep fertilization machine can result in the blockage of the working parts and damage to plant roots. In this study, a Super-large Fertilizer Granule (SFG) accelerator was designed for deep fertilization in the paddy field, in order to reduce the fertilizer loss with a high utilization rate. The high speed of the SFG was achieved in the release and long-term effectiveness of SFG. The high-pressure airflow was formed at the twin spiral inlet within an approximately closed space in the acceleration tube above the SFG. The SFG was accelerated to avoid the collision of the SFG on the wall of the accelerator tube as well, in order to reduce the speed loss of the SFG; The airflow was diffused at the outlet to reduce its speed and the impact on the soil, in order to improve the stability of fertilizer position. The structural parameters of the accelerator were determined using the physical parameters of SFG. The working parameters of the accelerator were analyzed to fully meet the requirement of the injection speed for the depth of fertilization. A simulation model was established for the accelerator using the Fluent platform. 6DOF overlapping dynamic grid was selected to simulate the flow field in the accelerating tube in the fluid domain. The single-factor experiments and three-factor three-level Box Behnken combination experiments were conducted with the inlet airflow speed, inlet spiral angle, and acceleration tube diameter as the experimental factors. A systematic investigation was implemented to explore the effects of the factors on the injection speed of fertilizer and the diffusion rate of outlet airflow. The regression model and response surface analysis of the test indexes were established by multifactor experimental analysis. The results showed the optimal working parameters were achieved in the accelerator: inlet airflow speed of 47 m/s, acceleration tube diameter of 21 mm, and spiral inlet angle of 43°, when the weight of the accelerator fertilizer injection speed was 0.6, and the weight of the outlet airflow diffusion rate was 0.4. The bench test was carried out using the 3D-printed SFG spiral accelerator, where the SFG was developed by National Institute of Biochar, Shenyang Agricultural University. The average fertilizer ejection velocity was measured to be 12.61 m/s, the average diffusion rate of outlet airflow was 85.5%, and the average depth of fertilizer into the soil was 4.68 cm, thus meeting the requirements for the deep fertilization of rice. There was a small relative error between the predicted value from the multi-factor regression and the experimental, indicating the more accurate optimization of the simulation test. This finding can provide a promising basis for designing the pneumatic machines of deep application for the super-large fertilizer granule in paddy fields.