关键词: 油菜, 开花性状, 无人机, 数字图像监测, 等花量线, 氮密交互

Abstract: Using visible‐light images，this study investigated the effects of nitrogen rate and planting density interaction on rapeseed flowering，and optimized their combination to enhance the economic and ecological value of the flowering period. A two‐factor randomized block field experiment was conducted with five nitrogen gradients（0，90，180，270，360 kg/ha）and four planting density gradients（300 000，525 000，750 000，975 000 plants/ha）. UAV digital images were used to establish the flower pixel area index（FPAI） dynamic equation for flowering process，and nitrogen‐density combinations were optimized with cumulative FPAI during full bloom（M_S2）and input cost as core indicators.Results showed that FPAI was significantly positively correlated with single‐plant flower quantity（R²=0.941 2—0.984 0）.Compared with no‐nitrogen control（N₀），nitrogen treatments（N 90—360 kg/ha）advanced the start of initial bloom（B_x），full bloom（F_x）and peak bloom（T_x） by 2.5，1.9 and 1.0 d，and extended initial bloom（S₁），full bloom（S₂）and theoretical flowering duration（S₁₊₂） by 0.6，1.5 and 2.1 d，respectively.Planting density had no significant effect on key flowering time points［F_x，T_x，E_x （the start of final bloom）］；increased density shortened S₁ and S₁₊₂ by 1.5 d and 1.0 d on average，but extended S₂ by 0.5 d.At fixed density，key flower quantity indicators all increased first and then decreased with rising nitrogen rate.The average values of theoretical maximum flowering accumulation（A），M_S2 and mean full‐bloom FPAI（MAve） under N 90—360 kg/ha treatments increased by 50.1%，64.7% and 48.1% compared with no nitrogen application treatment. When nitrogen application rate reached 360 kg/ha，increasing planting density would instead reduce flower yield.Cost optimization showed that combinations in optimized zone Ⅰ achieved the lowest input cost for target flower quantity. The optimal combinations were 580 000—780 000 plants/ha with N 157.7—195.9 kg/ha for high flower quantity，M_S2=197.2—203.1，cost 1 201.8—1 515.8 yuan/ha）；479 000—580 000 plants/ha with N 92.0—157.7 kg/ha for medium flower quantity，M_S2=176.5—197.2，cost 801.2—1 201.8 yuan/ha；438 000—479 000 plants/ha with N 55.4—92.0 kg/ha for low flower quantity，M_S2=155.7—176.5，cost 589.1—801.2 yuan/ha.Sub‐optimal combinations outside zone Ⅰ could reduce cost by 2.1%—16.0% via density‐increasing &nitrogen‐reducing or nitrogen‐increasing & density‐reducing strategies. In conclusion，FPAI is an effective indicator for monitoring rapeseed flowering dynamics. Rational nitrogen‐density synergy can increase flower quantity and regulate flowering process，with nitrogen rate playing a dominant role.The optimization zoning provides targeted nitrogen‐density configuration schemes，and offers decision support for cost‐saving and efficiency‐enhancing production of flower‐use rapeseed.

Key words: Oilseed rape, Flowering traits, Unmanned aerial vehicle, Digital image‐based detection, Flower quantity isoline, Nitrogen‐density interaction