Research progress in growth characteristics and key techniques for the high yield of unmanned aerial seeding rice

High-quality and efficient rice production via unmanned construction has been required in modern agriculture. Rice unmanned production can also be accelerated due to the shortage of labor supply at present. In particular, unmanned aerial seeding (UAS) has attracted extensive attention, due to its free of terrain, operating cost-saving, and high efficiency. However, the multiple cropping strategy has been practiced to confine the aerial seed emergence and growth in many rice regions, leading to compression of the rice growth period and a large amount of straw return to the field. This study aims to guarantee the stable and high yield of UAS. The research object was taken as the locally suitable varieties in the early stage. A series of experiments were conducted in the rice-wheat double-maturing region of Jiangsu Province, China. Firstly, rice production was compared between UAS and unmanned carpet-transplanting under straw-return conditions. Subsequently, three seedling treatments were set as 150×10⁴, 195×10⁴, and 240×10⁴ plants/hm² in UAS. The yield and quality were then evaluated among different population densities. The high-yield cultivation and techniques of UAS rice were summarized on the ecological, growth, and development. The UAS was initially identified with the following ecological characteristics: 1) There was a shortened growth period at low temperatures and light resources; 2) A large amount of straw returned to the field was caused by a low quality of tilled land, resulting in a seedling growth adversity; 3) The economic and ecological costs were reduced with the global warming potential to sustainable development. Besides, the growth and developmental features were obtained: 1) The individual growth was reduced to deteriorate the plant configuration, indicating the ever-increasing lodging risk; 2) There were main stems and tillers forming panicles, while a large wave in the population tiller number; 3) The yield level was restricted to a forward growth center and insufficient accumulation of population dry matter after spiking; 4) There was a deterioration in the rice processing, appearance, and nutritive qualities, whereas, the tasting qualities were improved. Some suggestions were given for the high-yield cultivation approaches. The optimal seedling density was achieved in 195×10⁴ plants/hm² for the UAS conventional japonica rice with both high yield and high quality under straw return. Moreover, the basic seedling and the proportion of main stem panicles were appropriately increasing under the panicle formation, considering both main stems and tillers suitable for cultivation management in favor of the stable and abundant yield of UAS conventional japonica rice. The key technologies of unmanned aerial sowing were also explored for the conventional japonica rice under the straw returning to the field, in terms of variety selection, seed processing, sowing period, tillage and furrow system, planting density, fertilizer and irrigation management, and plant protection. And the prospect for the future application of UAS technology was also proposed: 1) Drone technology can be realized to develop the long duration, lightweight models and new types of seeders; 2) Industry standards can be established to generalize the production of drone accessories; 3) Evaluation can be performed to optimize the distribution of UAS technology, according to regional adaptability. Adequate research can also be conducted on the high-yield and high-quality cultivation approaches. The finding can provide theoretical support for the large-scale application of UAS rice.