Abstract:
Sweet potato is an important food crop in the world. It is also a raw material for starch industry, and a health food to prevent cancer and a feedstock for bioenergy as well. The sweet potato planting area in China per year on average is usually 3 667 000 hm
2, accounting for 45% of the world′s planted area. Sweet potato is usually asexual propagation adopted with root tuber, stem cuttings are transplanted with high ridge in large fields. In order to improve the mechanization transplanting level of sweet potato in China and solve outstanding issues currently existed in mechanization transplanting of sweet potato such as more frequently tractors operation, wheels going in ditches easy to cause damage and break ridges, poor transplanting performance, etc., a type 2ZGF-2 sweet potato transplanting compound operation machine matched with high-powered tractor of 55.13-80.85 kW was developed. The machine can complete two ridges of rotary tillage, ridging, broken stubble, furrowing, transplanting, reshaping operation all at once. This reduced farm working times compared with traditional segment operating machine, saved energy and reduced roller compaction of farmland. The machine had standardized cultivation with row spacing of 900 mm, which was easily matched with the rear wheel track of large and medium tractors, avoiding damage to ridge and tuber. This machine also used the widely used insertion form “oblique insertion method” in sweet potato transplanting. The angel between stem exposed to the ground of sweet potato seedlings and ridge top surface after operation was 60°-70°. Non-zero speed transplanting principle was adopted, and motion trajectory of clip-on-chain was trochoid, which properly increased the operation speed of the transplanter as well. Meanwhile, in order to guarantee coordinated work among ditching of furrower, seedling of clip-on-chain, and compaction of roller, the distance between the back-end soil boundary point of furrower and confirmed planting point of clip-on-chain was 110 mm. The distance between the lowest point of disk roller and confirmed planting point of clip-on-chain was 118 mm. In order to avoid too large pressure damage to the top ridge, the designed width of narrow disc was 70 mm, which was 30% smaller than the conventional size. Through the research, it was clear that transplanting plant spacing was related to the diameter of driving wheel, slip rate of land wheel, chain link number among clip-on-chains and drive sprocket. Different numbers of teeth were used to replace the drive sprocket to achieve the convenience of adjusting the plant spacing within 210-300 mm. In this study, the optimal parameters tested for the two indexes which affected evaluation of sweet potato seedling cultivation quality were carried out. The order of the main factors affecting the quality of the seedling operation was obtained as follow: showing length of feeding>furrower depth>operating speed. The optimal parameters combination was determined as: showing length of feeding 140 mm, furrower depth, 80 mm, operating speed, 0.3 m/s. When the qualification rate of seedling angel was 97.9%, the qualification rate of transplanting depth was 98.2%, better to meet the requirements of the sweet potato machinery transplanting. This study not only supplied the sweet potato transplanting market with an urgent and practical tool, but also provided theoretical basis and reference for the innovation development and optimization of sweet potato transplanting machinery.