# 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  
The working principle of spiral fertilizer dischargers is as follows: the spiral blades rotate around the axis, and under the pushing of the blades, the fertilizer in the fertilizer box is transported to the fertilizer discharge port and discharged. Its structure is shown in Figure 1[7]. This fertilizer discharger has low requirements for the physical properties of fertilizers and can be flexibly used for the application of granular fertilizers and powdered fertilizers [8]. It is low in price and has a simple structure. It is suitable for a variety of fertilizers with different physical properties. The amount of fertilizer can be adjusted according to the user's needs. This simple structure is relatively uniform and stable when discharging fertilizer. However, when fertilizing at a low rotation speed, fertilizer quality fluctuates greatly and the fertilizer discharge is uneven. The work of international researchers focuses on studying the impact of the spiral blade structure and working parameters on the performance of spiral fertilizer dischargers through discrete element simulation, bench testing, or the development of new designs for spiral fertilizer dischargers and attempts to optimize their conveying effect by adjusting key structural and working parameters to improve the accuracy and stability of fertilizer discharge dosing. [PERSON] et al. [9] designed a conveying screw machine for the short-distance transportation of small-particle materials. Its structure is depicted in Figure 2. A bench test study on the filling rate at different screw speeds was conducted, and it was found that when the  
Figure 1: Structural diagram of spiral fertilizer discharger. Note: 1. fertilizer tank; 2. motor; 3. coupling; 4. fertilizer inlet; 5. spiral blade; 6. shell; 7. fertilizer outlet. speed is between 15 and 21 rpm, the filling factor remains within the range of 0.76-0.81, which means the machine has high accuracy when applied to fertilizer transportation. [PERSON] et al. [10] optimized the spiral distributor (SVD) working-body spiral screw (Figure 3) through multi-factor experiments to improve fertilizer discharge accuracy and reduce unevenness. When the fertilizer feed rate is 320 kg per hour, the optimal structural parameters of the spiral screw are a diameter of 49 mm, a pitch of 1.05d (51.45 mm), and a gap of 2.5 mm, and the coefficient of variation in the fertilizer discharge stability does not exceed 0.2%; Meanwhile, when the fertilizer feed rate is 1450 kg per hour, the parameters are a diameter of 90 mm, a pitch 1.25 times the diameter (112.5 mm), and a gap of 7.5 mm. The coefficient of variation in the fertilizer discharge stability does not exceed 0.4%. [PERSON] et al. [11] compared the performance of two nitrogen, phosphorus, and potassium granular fertilizer formulas in a spiral fertilizer discharg at three operating speeds. During the experiment, an automated workbench was built to evaluate the performance of single-spiral and double-spiral fertilizer discharges, as shown in Figure 4. Two nitrogen, phosphorus, and potassium granular fertilizer formulas (04-14-08 and 04-30-10) were selected for the experiment and tested at different angular velocities. After the test was completed, the flow data were collected for statistics and analysis. It was concluded that as the speed increases, the single-spiral fertilizer discharger shows greater uniformity compared to the double-spiral fertilizer discharger. Although the speeds of 7 and 10 kph increased the flow rate of both granular fertilizers, as expected, the 04-30-10 fertilizer obtained the most even distribution at the lowest speed of 4 kph. Figure 3: Spiral distributors with different structures. Figure 2: Spiral fertilizer dischargers test diagram. The work of Chinese researchers primarily centers on the design and optimization of the structure and working parameters of spiral blades.