Increasing plant density increased rice (Oryza sativa) yield but decreased lodging resistance when grown under wheat (Triticum aestivum) straw using unmanned aerial seeding technology

Context Unmanned aerial seeding (UAS) of rice (Oryza sativa) has inherent advantages, but may not achieve a high and stable yield when extensive stubble is returned. Aims This study aimed to determine the optimal planting density for achieving high yield and lodging resistance in UAS rice. Methods The experiment evaluated yield and lodging of two rice varieties (conventional japonica and hybrid indica–japonica) at four planting densities 105 (D1), 150 (D2), 195 (D3), and 240 (D4) seedlings m−2 for conventional japonica; 45 (D1), 82.5 (D2), 120 (D3), and 157.5 (D4) seedlings m−2 for hybrid indica–japonica). Key results Our results showed that yield initially increased and then decreased with increasing density, and the highest yield was obtained under treatment D3. Increasing planting density increased the proportion of main stem panicles and the effective panicles, but decreased the number of grains per panicle, seed setting rate, and 1000-grain weight. The population growth rate was lower in seeding-jointing and heading-maturity stages for treatments D1 and D2, higher in seeding-jointing stage for treatment D4 but insufficient in subsequent stages, while treatment D3 had higher population growth rate throughout the whole growth stage, especially in heading-maturity stages, ultimately achieving high yield. Densification led to a reduction in plant height and ear length, as well as slender internodes and thinner base wall. Conclusions A planting density of 195 seedlings m−2 was optimal for conventional japonica rice, and 120 seedlings m−2 for indica–japonica. Implications Achieving high yield of UAS rice can be facilitated by increasing planting density, but may compromise lodging resistance.