# 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 working principle of air-feed fertilizer dischargers is as follows: the fertilizer discharger utilizes a mechanical device for fertilizer supply, followed by fertilizer transportation through high-speed airflow. The gas-fertilizer mixture is thoroughly mixed in the mixing area via the high-speed airflow, and then the evenly mixed gas-fertil mixture is transported to the fertilizer discharge pipe. The structure is illustrated in Figure 32. This method of fertilizer discharge enables a better flow of fertilizer, improved mixing performance, more stable fertilizer discharge, a simple overall structure, and enhanced efficiency in fertilization operations [49]. The work of international researchers focuses on using fluid dynamics modeling and simulation and calculation methods in the fields of pneumatic seeders and agricultural fertilizer discharges to examine whether fertilizer discharge meets the standards of precise fertilizer distribution. [PERSON] et al. [50] established a linear calculation mathematical model of the pneumatic seeder system using MathCAD 8.0, as illustrated in Figure 33. The system and design plan were detailed. Employing continuum mechanics, a parameter calculation method was proposed to validate the design decisions. By applying linear calculation to the series-parallel arrangement part, the linear calculation and structural indicators were redefined. The results indicate that the standard deviation of the air velocity within the section does not exceed 14%, and the standard deviation of the pressure on the section does  
Figure 31: Structural diagram of centrifugal, conical disc fertilizer discharger. Note: 1. centrifugal conical disc cover; 2. centrifugal conical disc. Figure 32: Structural diagram of air-feed fertilizer discharger. Note: 1. fertilizer discharge pipe; 2. air and fertilizer separation device; 3. corrugated pipe; 4. distribution outlet; 5. distribution device; 6. fertilizer box; 7. motor; 8. fan; 9. airflow conveying pipe; 10. air-fertilizer mixing device; 11. mechanical fertilizer discharge device; 12. air-fertilizer delivery pipe; 13. layered deep fertilization shovel. not surpass 0.5%. The analytical model exhibited high accuracy, with a mass flow error of only \(1.152\times 10^{-14}\%\). [PERSON] et al. [51] utilized numerical simulation calculations and experimental comparisons, as depicted in Figure 34, to validate the performance of two different types of radial fans in agricultural fertilizer dischargers at a rotation speed of 4000 rpm. Following the determination and validation of the mathematical model, the operational process of the fertilizer discharger was simulated, and the airflow distribution of the fertilizer discharg nozzle was assessed. Through experiments, it was observed that the numerical simulation yielded relatively accurate results, with an average error of 4.3%. The work of international researchers centers on designing and optimizing the structure and working parameters of fertilizer distribution devices and air distribution devices of air-feed fertilizer dischargers. The Hertz theory, CFD fluid simulation, and CFD-DEM air-solid coupling analysis methods were employed to optimize the parameters of the fertilizer distribution device and air separation device, demonstrating improved stability in fertilizer distribution. [PERSON] et al. [52] investigated the air-feed fertilizer discharger system of an oil-wheat seeder. Based on the [PERSON] theory, they established an elastic collision model for fertilizer particles and distribution devices. Employing CFD and DEM air-solid coupling methods, they separately analyzed the movement of fertilizer particles and their impact on the fertilizer discharge performance across four types of distribution devices.