Development of the profiling up-film transplanter for sweet potato in hilly and mountainous region

Sweet potato is one of the most favorite crops that is widely cultivated from the tropical to temperate regions. There is an ever-increasing need to produce more sweet potatoes on the existing arable land under the challenges of labor scarcity and population growth. However, it is still lacking the optimal machinery to transplant the spring sweet potato seedlings on mulched ridge planting system, especially in the hilly and mountainous region of northern China. In this study, a profiling transplanter was designed for the "shallow planting and multiple buried joints" of sweet potato seedlings, according to the agronomic requirements of "shallow cultivation and multiple burying nodes". The boat-bottom planting placement of mulch raised the beds' cultivation system of sweet potatoes. The space-time coordination and working parameters of the transplanting unit were optimized to consider the transplanting angle, transplanting depth, seedling length under the film and hole length. Indoor and outdoor tests were also carried out to verify the model. The indoor seedling-taking tests showed that the planting unit posed the super seedling taking effect on the five sweet potato varieties, which were widely planted in Huang-Huai-Hai area. More narrowly, the seedling picking success rates of the planting unit were more than 99% under the rotating speeds of 40-50 r/min, which fully met the needs of field operation. Furthermore, the orthogonal experiment of field transplanting was carried out in the field, in which the influencing factors were taken as the operation speed, the shape of sweet potato seedlings base, the length of seedlings extending out of the brush, and the average number of buried nodes, the qualified rate of transplanting depth, and the missing rate determined as the evaluation indexes. The field experiment showed that the influence factor on the average number of buried nodes was ranked in the descending order of the length of seedlings extending out of the brush, the operation speed, and the shape of the sweet potato seedlings base. By contrast, the influence factor on the qualified rate of transplanting depth was the length of seedlings extending out of the brush, the shape of the sweet potato seedlings base, and the operation speed. The influencing factors on the missing seedling rate were the operation speed, the shape of sweet potato seedlings base, and the length of seedlings extending out of the brush. The operating parameters were optimized using fuzzy evaluation and range analysis. As such, each factor on the comprehensive score of field experiment performances was ranked in the descending order of the length of seedlings extending out of the brush, the shape of the sweet potato seedlings base, and operation speed. The optimal combination of parameters was as follows: the operation speed of 0.5 km/h, the most upright sweet potato seedlings base, and the extension length of sweet potato seedlings of 60 mm. Finally, the transplanting efficacy of the sweet potato seedlings profiling transplanter was evaluated under the optimal operation parameters in the hilly and mountainous regions. The results showed that the average transplanting depth, the transplanted seedling length under the film, the hole length, and the transplanting angle were 73.6, 205.4, 76.5 mm and 53.8°, respectively. Meanwhile, the transplanting space variation coefficient, the qualified rate of planting depth, and the rate of missing seedlings were 8.9%, 93.7%, and 3.5%, respectively. The performance fully met the agronomic requirements of "shallow cultivation and multiple burying nodes" for the boat-bottom planting placement and the regulations of transplanting quality on dry land transplanting equipment. This finding is of considerable importance to developing the transplanting machine for planting spring sweet potato seedlings on mulched ridge planting systems in the hilly and mountainous regions of northern China, as well as for sustainable development of the sweet potato industry.