## 4 Discussion  
1. In the actual operation process of the traditional spiral fertilizer applicator, the filling coefficient does not change linearly with the rotational speed change. Therefore, to achieve precise fertilizer discharge, this article designs a spiral-pushing fertilizer applicator, which mainly changes the pitch and diameter of the existing spiral fertilizer applicator, so that its instantaneous filling coefficient is in a fixed state of full filling. Based on the movement trend for fertilizer particles in the spiral cavity, the main factors affecting the movement characteristics of fertilizer particles were determined to be the spiral diameter, pitch, and rotational speed. Through EDEM, a simulation model of the spiral-pushing fertilizer applicator was established to analyze the fertilizer discharge status during the fertilizer discharge process of the spiral-pushing fertilizer applicator. A quadratic orthogonal rotation combination design experiment was conducted with the filling coefficient and particle axial velocity coefficient as experimental indicators and the spiral pitch elongation percentage, spiral diameter elongation percentage, and rotational speed as experimental factors. 2. The experimental results show that the spiral pitch elongation percentage and spiral diameter elongation percentage have a significant impact on the filling coefficient. In contrast, the spiral pitch elongation percentage and rotational speed have a significant effect on the particle axial velocity coefficient. Based on the experimental results, the parameters of the spiral-pushing fertilizer applicator were optimized. The results showed that when the spiral pitch elongation percentage was 189.82-200%, the spiral diameter elongation percentage was 102.75-106.76%, and the rotational speed was 30 r/min, the filling coefficient was 97.24%, and the particle axial velocity coefficient was 7.61%. The traditional spiral fertilizer applicator has a filling coefficient of 52.09% at a rotational speed of 30 r/min. This indicates that under a low rotational speed, the spiral-pushing fertilizer applicator has a high filling coefficient and good fluidity of fertilizer particles in the spiral cavity. 3. To verify the correctness of the optimization results, a comparative test was conducted through bench tests on the spiral-pushing fertilizer applicator and the spiral fertilizer applicator. The results show that the fitting equation \(R^{2}\) = 0.99 for the spiral-pushing fertilizer applicator flow rate and the fitting function equation \(R^{2}\) = 0.98 for the traditional spiral fertilizer applicator discharge flow rate. This proves that the spiral-pushing fertilizer applicator discharge performance was significantly better than the traditional spiral fertilizer applicator discharge during bench tests. It was feasible to achieve precise fertilizer discharge by improving the spiral cavity filling co  
Figure 14: Comparison curve of fertilizer discharge flow rate of electrically controlled fertilizer discharge device. efficient. Based on the discharge flow curve of the spiral-pushing fertilizer applicator y = 0.486\(\times\) 1.7417, an electrically controlled fertilizer discharge system was designed and tested on a bench. The bench test results showed that the spiral-pushing fertilizer applicator controlled by the electrically controlled fertilizer discharge system had a high precision in fertilizer discharge, and the rotational speed could accurately adjust the fertilizer discharge flow to meet the fertilizer demand in the fields. [PERSON] and [PERSON] designed the research. [PERSON], [PERSON] and [PERSON] participated in the measurements and data analysis, and [PERSON] wrote the first draft of the manuscript. [PERSON] and [PERSON] revised and edited the final version of the manuscript. [PERSON] was responsible for funding acquisition. All authors have read and agreed to the published version of the manuscript.