Mechanical transplanting has been limited to the blanket seedling cultivation, due to the heavy weight of seedling substrates, high labor intensity, and the large number of seedling trays. In this study, the high-density seeding was employed to replace the conventional seedling soil with the lightweight crop straw boards. The mechanic transplanting was then enhanced the seedling quality and transplanting performance. The labor inputs were also reduced to promote the rice blanket seedling. The japonica rice cultivar ‘Nanjing 5718’ was taken as the test material. A conventional seeding density (D1: 150 g/tray) was evaluated under four high-density treatments (D2: 200 g/tray; D3: 250 g/tray; D4: 300 g/tray; and D5: 350 g/tray) and four seedling ages (A1: 10 d; A2: 15 d; A3: 20 d; and A4: 25 d). The investigation focused mainly on the seedling growth, physiological attributes, mechanical transplanting quality, yield, and economic returns. Results indicated that the key indicators of seedling quality—such as the soluble sugar content, root activity, and rooting ability—declined with increasing seedling age under high-density treatments (D2–D5). These indices were even better at the shorter seedling ages (10 and 15 days) than those of the conventional combination (D1A3). The high-density seeding was integrated with the vigor in the early growth stage, when the seedlings relied primarily on the nutrient reserves in the endosperm, together with the lower demands for the light and temperature. The higher activities of protective enzymes were observed under high density at 15 days, including the superoxide dismutase (SOD) and peroxidase (POD), indicating the enhanced stress tolerance; Whereas, the malondialdehyde (MDA) content was signified to heighten the oxidative stress, with the longer seedling ages, due to the intensified competition for the limited nutrients. Furthermore, the missing hill rate in the high-density treatments decreased by 19.78%–60.26%, compared with the conventional D1 treatment, thus leading to the more uniform pattern of mechanical transplanting. Although the seedling injury rate increased by 32.25%-242.90%, due to the increased inter-plant competition. The floating seedling and lodging rates were reduced by 15.01%-50.55% and 17.53%-45.44%, respectively, during mechanical handling. The transplanting quality was shorten the recovery period post-transplant and support sustained crop growth. The ultrahigh density was also reduced the number of seedling trays per unit area, which was dropped by 12.12%–58.98%, compared with the conventional. The lower labor and material costs were directly reduced correspondingly. Notably, the D4A2 combination (300 g/tray with a 15-day seedling age) yielded the best overall performance, thus producing 10.69 and 10.65 t/hm² over two consecutive years, with the highest economic returns of 32 085.32 and 31 967.25 Yuan/hm². In summary, the high physiological quality and mechanical performance of transplanting were achieved in the ultrahigh density seedling cultivation with the crop straw boards under shorter seedling age. The required number of seedling trays was effectively reduced to enhance the overall economic benefits. The synergistic effect between high-density seeding and early transplantation can provide a promising strategy to advance the mechanized rice production in the more sustainable, cost-effective agricultural practices. In conclusion, the lightweight crop straw boards with the ultrahigh density seeding at the optimal seedling ages were significantly enhanced the efficiency and sustainability of mechanized rice cultivation

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.

The high labor demand during rice seedling cultivation and transplantation poses a significant challenge in advancing machine-transplanted rice cultivation. This problem may be solved by increasing the seeding rate during seedling production while reducing the number of seedling trays. This study conducted field experiments from 2021 to 2022, using transplanting seedling ages of 10 and 15 days to explore the effects of 250,300, and 350 g/tray on the seedling quality, mechanical transplantation quality, yields, and economic benefits of rice. The commonly used combination of 150 g/tray with a 20-day seedling age in rice production was used as CK. The cultivation of seedlings under a high seeding rate and short seedling age significantly affected seedling characteristics, but there was no significant difference in seedling vitality compared to CK. The minimum number of rice trays used in the experiment was observed in the treatment of 350–10 (300 g/tray and 10-day seedling age), only 152–155 trays ha^–1, resulting in a 62% reduction in the number of trays needed. By increasing the seeding rate of rice, missed holes during mechanical transplantation decreased by 2.8 to 4%. The treatment of 300–15 (300 g/tray and 15-day seedling age) achieved the highest yields and economic gains. These results indicated that using crop straw boards can reduce the application of seedling trays. On that basis, rice yields can be increased by raising the seeding rate and shortening the seedling age of rice without compromising seedling quality.

In the face of agricultural labor shortages, reducing labor and costs in rice production while meeting demand or increasing yield is crucial for sustainable agricultural development. Using crop straw boards and raising seedlings at a high-density can reduce labor demand and enhance rice yield. This study investigated the effects of seeding density and transplanting age on tillering patterns, panicle formation rates, and yield to determine the optimal cultivation practices for maximizing rice yield. Two-year field experiments were conducted in Sihong County, Jiangsu Province, China, using the japonica rice variety Nanjing 5718. Five seeding densities (150–350 g/tray) and four transplanting ages (10–25 days) were evaluated to assess their impacts on tillering patterns, panicle formation rates, and yield. Innovative crop straw boards were employed to enhance planting efficiency and reduce dependence on soil for raising seedlings. This approach also lessened tillage layer destruction, promoting sustainable practices. The results indicated that increasing seeding density significantly altered tillering and panicle formation patterns by reducing the occurrence and panicle formation rates of lower-position tillers. Although the occurrence of middle- and high-position tillers increased, the overall number of panicles per hill decreased, especially at higher densities, negatively affecting yield. Reducing the transplanting age promoted the emergence and panicle formation of lower-position tillers, thus mitigating these negative effects. Specifically, compared to traditional methods (150 g/tray, 20-day seedlings), the higher seeding density (300 g/tray) and reduced transplanting age (15-day seedlings) increased total panicle number by 3.79–4.73% and yield by 3.38–5.05%. Combining higher seeding densities with reduced transplanting ages offers significant advantages over conventional practices by enhancing resource utilization and improving tillering efficiency. These findings provide actionable recommendations for optimizing rice cultivation practices and contribute to sustainable agricultural development.