Characteristics of Plant Type and Lodging Resistance in Unmanned Aerial Seeding Rice With Optimal Basal Seedlings

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.