# Research Progress Regarding the Precision of Dosing and Distribution Devices for Fertilizers
## 2 Current Status of Research on Precision Fertilizer Dischargers
### Research Status of Air-Feed Fertilizer Discharge
The structure of the distribution device is depicted in Figure 35. The findings reveal that the dome distribution device exhibits a superior fertilizer discharge performance, with the coefficient  
Figure 34: Two different types of radial fans: (**a**) A1 radial fan; (**b**) B1 radial fan. Note: A is the entrance; B is the exit. 1. fan; 2. volute; 3. air distribution box. Figure 33: Installation diagram of pneumatic conveying system of pneumatic seeder. Note: 1. fan installation position; 2. air duct; 3. nozzle; 4. seed metering device; 5. horizontal pipe section; 6. bend pipe; 7. vertical pipe section; 8. guide; 9. distributor; 10. delivery pipe (hose); 11. coulter; 12. coulter nozzle. of variation of fertilizer discharge consistency in each row fluctuating between 6.35% and 7.52%. [PERSON] et al. [53] investigated a pneumatic centralized discharge precision mixing fertilization device for corn, integrating the research of CFD and DEM air-solid coupling methods. They utilized nitrogen, phosphorus, and potassium fertilizers as the test fertilizers and conducted a three-factor and two-level regression orthogonal combination design test. The optimized structural parameters are a fertilizer outlet inclination angle of 45 degrees, a conveying air speed of 35 mps, and a bellows length of 568 mm. The structure is depicted in Figures 36 and 37. Subsequently, field trials were carried out, managing to control the error of fertilizer application within 2%, with a stability coefficient of variation of approximately 2%, meeting national standards. Figure 36: Schematic diagram of the overall structure of the fertilizer distributor. Note: L is the length of the bellows. 1. fertilizer pipe; 2. fertilizer distributor. Figure 35: Schematic diagram of the longitudinal section of the main body of different distribution devices: (**a**) flat-top type; (**b**) flat-top inverted cone type; (**c**) dome type; (**d**) dome inverted cone type. [PERSON] et al. [54; 55] utilized CFD fluid simulation to enhance the performance of the air distribution device within the pneumatic fertilizer conveying system in rice fields. Its structure is depicted in Figure 38. It is concluded that the opening angle of the baffle significantly affects the air separation performance, and at an opening angle of 48 degrees, the flow rate consistency of the exhaust port is optimal, with a fertilizer distribution variation coefficient of 5.65%. Concurrently, the connection method of the air-fertil mixing device was refined, with the feed pipe being connected and extended into the trachea at an inclined angle, thereby increasing the flow rate. Through the CFD-DEM air-solid coupling simulation test, it was observed that the optimized air-fertil mixing device increased the speed of urea particles by 93.6%. The above research uses the Hertz theory, CFD fluid simulation, and CFD-DEM air-solid coupling analysis methods to compare and analyze various types of fertilizer distribution devices of air-fed fertilizer dischargers. The parameters such as the discharge outlet inclination angle, conveying air speed, bellows length, and opening angle of the air distribution device were optimized, effectively enhancing the precision of fertilizer distribution and reducing unevenness and breakage rates during fertilizer discharge, which has a reference value for future studies.