# Research Progress Regarding the Precision of Dosing and Distribution Devices for Fertilizers
## 2 Current Status of Research on Precision Fertilizer Dischargers
### Research Status of Spiral Fertilizer Dischargers
Using a method that combines discrete element simulation with bench and field trials, the parameters of the spiral blades are continuously optimized to improve the stability and uniformity of fertilizer discharge dosing. [PERSON] et al. [12; 13; 14] designed a small-scale spiral quantitative fertilizer discharger, examining the discharge process of three types of fertilizers (urea, compound fertilizer, and organic fertilizer) through discrete element simulation. They established a mathematical model and conducted single-factor and quadratic regression orthogonal rotation combined tests. The order of factors affecting the fertilizer discharge amount is as follows: fertilizer discharge shaft rotating speed, pitch, and spiral blade diameter. Combined with bench testing, optimized parameters were determined to be a diameter of the spiral blade (as shown in Figure 5) of 92 mm, a pitch of 56 mm, and a rotation speed of the fertilizer discharge shaft of 39 rpm. The stability and uniformity of fertilizer discharge were found to be satisfactory, with the measured average coefficient of variation of fertilizer discharge stability at 12.25%. The average relative error between the simulation and experiment was 8.51%. Fertilization in mango orchards meets the requirements well. [PERSON] [15] employed discrete element simulation to investigate the organic fertilizer discharger, with the aim of revealing the movement process of fertilizer particles within it. Additionally, the study aimed to analyze the correlation between the amount of discharged fertilizer and both the rotation speed of the discharge shaft and the number of pitches in the variable diameter and variable pitch section of the shaft's feeding section. The structure of the fertilizer discharge shaft is illustrated in Figure 6. Through two-factor and three-level simulation tests along with field trials, it was concluded that the rotation speed of the  
Figure 4: Diagonal projection of the electronic and automated bench. Note: A. electrical control; B. transmission set; C. articulation; D. respiratory; E. spiral fertilizer discharges; F. data acquisition system. I. single spiral fertilizer dischargers; II. double spiral fertilizer dischargers. Figure 5: Approximate expansion view of spiral blades. Note: \(\alpha\) is the helix angle, \(S\) is the thread pitch, \(D\) is the diameter of the spiral blade at a certain point. fertilizer discharge shaft has a more significant impact on the discharged fertilizer amount compared to the number of pitches in the variable diameter and variable pitch section of the shaft. Notably, when the number of pitches in the feeding section of the fertilizer discharge shaft is set at three, the stability variation coefficient of fertilizer discharge can be reduced to the minimum level, ranging from 6.93% to 7.50%, aligning with relevant industry standards. [PERSON] et al. [16; 17] devised a four-head, spiral, double-row fertilizer discharger tailored for rapeseed cultivation. The structure of the fertilizer discharge spiral blade is depicted in Figure 7. They executed single-factor discrete element analysis experiments aimed at simulating the movement of compound fertilizer particles within the fertilizer discharger. Through comparative experiments and iterative optimization, it was ascertained that the four-head fertilizer discharge spiral configuration should be adopted, with optimal performance achieved at a pitch of 24 mm. Combining bench and field trials, it was deduced that maintaining a fertilizer discharge spiral blade speed within the range of 40 to 60 rpm ensures that the variation coefficient of the fertilizer discharge uniformity for the three fertilizers remains below 6.8%. Additionally, the stability of the total fertilizer discharge and the consistency coefficient of variation for the double-row fertilizer discharge do not exceed 2.6%.