A mixture of controlled-release nitrogen (N) fertilizers (CRNFs) and conventional urea (CU) as a single application of basal fertilizer could simplify fertilization in rice cultivation from the traditional and more labor-intensive fertilization strategy of multiple applications of nitrogen. However, the reported benefits of this combined approach in increasing rice yield have varied substantially for various reasons, including that various types of rice are characterized by different N requirements to obtain high yield. In this study, two late japonica rice cultivars, Jia58 (J58) and Jia67(J67), were used to determine the best combination of one of two short-acting CRNFs (release periods were 40 and 60 days) and one of three long-acting CRNFs (release periods were 80, 100 and 120 days) to apply with the CU as a one-time application of basal fertilizer. Six combinations of CRNFs were established based on their release periods: A1, 40 + 80 days; A2, 40 + 100 days; A3, 40 + 120 days; B1, 60 + 80 days; B2, 60 + 100 days; and B3, 60 + 120 days. CU applied split at basal, tillering and panicle differentiation stages, respectively as control (CK). The effects of the different treatment combinations of CRNFs on late-rice grain yield, N accumulation and N-use efficiency in a two-year field experiment were determined. Results showed that, the A2 treatment achieved the same yield as that of CK, and yield of the B2 treatment exceeded the yield of CK. Yield of J58 applied with B2 was 7.35% higher in 2018 and 7.40% higher in 2019 than that of the corresponding yield of CK; yield of J67 applied with B2 was 6.05% higher in 2018 and 6.87% higher in 2019 than that of CK. Compared with other CRNF treatments, the release of N from A2 and B2 was most synchronized with nitrogen uptake by the two cultivars, which indicates that fertilizer combination completely met the nitrogen demands during each growth stage of rice. Rice of the A2 and B2 treatments had higher N accumulation, higher aboveground biomass accumulation and LAI (leaf area index) at the heading and maturity stages and higher photosynthetic activity than those of other CRNF treatments. In conclusion, for late japonica rice in China, the application of the A2 and B2 treatments as optimal type of CRNF can achieve labor saving and yield increasing simultaneously in rice production.

Unmanned aerial seeding (UAS) is an efficient unmanned rice planting method with broad application prospects. But its optimum basic seedling number and yield and quality characteristics remain unclear. Field experiments were conducted to compare UAS, unmanned dry direct seeding (UDDS), and unmanned carpet transplanting (UCT) methods using inbred japonica rice variety Nanjing 5718. The UAS method was subdivided into four planting density treatments (UAS105, UAS150, UAS195, and UAS240 = 105, 150, 195, and 240 seedlings/m², respectively). The results showed that increasing the basic seedling density first increased the yield but then it decreased, and UAS195 produced a significantly higher yield. On the other hand, the grain processing, appearance, and taste quality deteriorated with improved nutritional quality. Among the three planting methods, UAS (UAS195) yielded less than UCT due to there being fewer spikelets per panicle, a lower grain-filling rate, and less photosynthetic activity after heading. However, UAS (UAS195) produced more yields than UDDS by having more panicles, more spikelets per panicle, and more biomass accumulation. Both UAS195 and UDDS had poorer grain processing, appearance, and nutritional quality than UCT, but increased amylose content and taste values. Therefore, UAS195 could be an alternative planting method for inbred japonica rice with coordinated yield, quality, and production efficiency.

The excessive application of nitrogen (N) fertilizer can result in soil and water pollution, thereby negatively impacting the ecological environment. However, reducing the amount of N fertilizer may lead to a decrease in crop yield. Two years’ experiment (2021 and 2022) investigates the influence of one-time reduced basal application of controlled-release N fertilizer (CRU) and increased planting density on the grain yield and N utilization characteristics of mechanically transplanted japonica rice. Nanjing 5718 was used as the experimental material. Under the condition of 225 kg ha⁻¹ of N, three controlled-release periods of CRUs (60d, 80d, 100d) and three planting densities (6, 8, and 10 seedlings/hole) were combined, totaling nine combinations. Moreover, a conventional split fertilization treatment with 300 kg ha⁻¹ of N and a planting density of 4 seedlings/hole was set as the control (CK). The yield, dry matter accumulation, N accumulation, and N utilization efficiency were evaluated. The research findings demonstrate that the CRU80-6 treatment exhibited the highest efficacy among all N reduction and density increase treatments, resulting in a significant yield increase of 3.1–10.3% compared to other treatments. After the jointing stage, the CRU80-6 treatment exhibited the highest dry matter accumulation compared to other treatments, with an increase ranging from 0.8% to 13.6%, and was significantly lower than that of the CK by 4.3% to 5.0%. The N accumulation and translocation traits of the CRU80-6 treatment closely resembled those of CK. However, both N recovery efficiency (NRE) and N agronomic efficiency (NAE) exhibited a remarkable increase compared to CK, with an average enhancement in NRE of 30.01%. Therefore, we contend that the CRU80-6 treatment, with a 25% reduction in N input, can ensure efficient N utilization and attain a relatively stable grain yield.

Unmanned aerial seeding (UAS) is a promising rice direct seeding method with excellent regional adaptability, operational efficiency, and economic benefits. To characterize the plant type and lodging resistance of the optimal UAS population and to distinguish it from other unmanned planting methods, a 2‐year field experiment was conducted. Four UAS populations (UAS105, UAS150, UAS195 and UAS240 = 105, 150, 195 and 240 seedlings m⁻²) were established using the inbred japonica cultivar Nanjing5718 as the material, and the appropriate unmanned populations of dry direct seeding (UDDS) and carpet transplanting (UCT) were employed as controls. The results showed that more UAS basic seedlings caused lower grain yield per panicle (9.56%–29.48%), worse leaf and culm configurations, and higher lodging risk (2.43%–9.11% and 0.86%–10.60% in the 2nd and 3rd basal internodes, respectively). But the proper increase (UAS195) improved population yield (3.38%–16.52%), leaf area index (LAI) and grain‐leaf ratio. Among the methods, UAS195 ranked behind UCT in all aspects of plant type and lodging resistance, as well as population yield and grain‐leaf ratio, and only the LAI excelled. However, it produced more population yield (4.86% on average) and larger panicles (2.02% on average in grain yield per panicle) than UDDS, due to the larger basal and drooping angles, longer pillow distances, and higher SPAD values in high‐efficiency leaves, more LAI, and grain‐leaf ratio. Furthermore, UAS195 had taller plant height, gravity center height, and basal internodes with more bending moment, but its relative gravity center height and lodging index did not deteriorate significantly. This was attributed to increased breaking strength from stronger internodes with thicker walls. The findings suggest that the optimal increase in UAS basic seedlings (UAS195) could produce more population yield by improving photometric area and grain‐leaf ratio, despite compromises in plant type and lodging resistance. Furthermore, not comparable to UCT, but it provides better vertical canopy structure and population yield than UDDS and maintains similar lodging resistance.