# Design and Experimental Study of Potato-Soil Separation Device for Sticky Soils Condition
## 5 Discussion and Conclusions  
In this paper, we developed a new type of potato-separation device comprising five function areas (i.e., shearing, bending, throwing, cleaning, and conveying) to address the problem (e.g., potato-soil separation under sticky soils condition). Given the kinetic analyses for the potato-soil mixture of five function areas, the crucial factors of the effect of potato-soil separation were determined. Then the run parameters of the device were optimized by conducting an orthogonal test. Toothed roller is the key component of the soil-crushing mechanism and was expected to shear the sticky soil. The structure and function of the toothed roller in this paper are somewhat similar to the finger wheel in poke finger's wheel type potato harvester [24], but the roller in this paper was mounted above the lifting chain, and there is a movement match with the lifting chain, the shear and transport modes of potato-soil complex are different. As revealed from the results of the single factor test, after the soil-crushing mechanism installation, the percentage of small soil \(\lambda\) was increased from 65.24% to 82.21%, which indicated that the shearing and impact effect on potato-soil mixture of soil-crushing mechanism elevated the shattering degree of the potato-soil mixture. However, the use of a soil-crushing mechanism up-regulated the damage degree of potato tuber. The damage rate of potato tuber \(K\) declined from 6.13 to 3.62% when the soil-crushing mechanism was disassembled, that we believe is also caused by shearing and striking effect on potato tubers of soil-crushing mechanism. The results of orthogonal test showed that the optimal run parameters included the rotational speed of the soil-crushing mechanism of 84.18 r/min; linear velocity of second-stage lifting chain of 0.75 m/s and inclination angle of lifting chain of 15.87\({}^{\circ}\). The rotational speed of 84.18 r/min made the linear velocity at the tip of roller tooth slightly faster than that of the lifting chain, which could not only ensure the delivery, but also minimize the impact of roller teeth on potato tubers. According to the results of previous studies, the recommended linear velocity of the lifting chain was found to be at the range of 1.0-2.2 m/s [25; 26; 27], and the inclination angle at the range of 20-24\({}^{\circ}\)[25; 27; 31]. Lower values of the optimal parameters were obtained in this study. We believe that was caused by the characteristics of paddy clay soil; sticky soil needs longer sieving time so as the delivery velocity should be slower, and the smaller inclination angle will be good for the lifting and sieving of the heavy soil. Figure 13: Field harvesting test. (**a**) Modified prototype; (**b**) harvesting effect. The field experiments were performed by the modified potato harvester with the condition of soil moisture content of 20.06%. As revealed from the result, the visible potato rate took up 94.31%; the damage rate of potato was 0.89%. We referred to other studies that were conducted according to the same standard (NY/T 648-2015), the poke finger's wheel type potato harvester mentioned above was tested in the field, and the visible potato rate was 96.5%; the damage rate of potato was 4.5% [24], while the test conducted in the condition in which the soil moisture content was 12%. In the field test of another crawler self-propelled potato harvester under the condition of 20% soil moisture content, the visible potato rate was 98.54% and the damage rate of potato was 1.31% [35], while the test site is located in northwest of China, where the soil is sandy rather than clay. The results of field experiments show that the visible potato rate was lower when harvest potato in wet and sticky clay soil compared to with sandy soil and dry soil, which was consistent with practical common sense. The potato harvester in this study obtained a lower damage rate of potato, which may be related to the buffering effect of sticky soil.