Abstract: To elucidate the synergistic regulatory mechanisms of sowing dates and chemical topping dates on the optimization of plant population structure，enhancement of photosynthetic efficiency，and yield formation in summer⁃sown short⁃season cotton，and to establish a simplified and efficient cultivation model suitable for the Yangtze River Basin，a two⁃site，one⁃year field experiment was conducted in 2024 in Hekou Town，Linli County，and Huanggai Town，Linxiang City，Hunan Province. Using the early⁃maturing cotton variety Xiangnongzao No.1 as the test material，a two⁃factor randomized block design was employed，with three sowing dates［May 25（S1），May 30（S2），June 4（S3）］and four chemical topping dates［June 25（T1），July 2（T2），July 9（T3），July 16（T4）］.Key indicators，including population structure，photosynthetic characteristics，and yield formation，were systematically measured.The results indicated that sowing date，chemical topping date，and their interaction significantly affected population structure，photosynthetic characteristics，and yield formation.Among these，the treatment combining sowing on June 4 with topping on July 9（S3T3） exhibited the best overall performance：the leaf area index was maintained between 2.45 and 2.60，with dry matter accumulation per plant increasing by 17.5%（Huanggai Town） and 22.8%（Hekou Town） compared to the S1T1 treatment，photosynthetically active radiation（PAR）in the canopy increasing by 44.5%（Huanggai Town）and 27.9%（Hekou Town），and net photosynthetic rate increasing by 64.4%（Huanggai Town）and 75.1%（Hekou Town）；regarding yield components，S3T3 treatment resulted in a synergistic increase in both the number of bolls and boll weight compared to all other treatments，thereby achieving the optimal seed cotton yields in both Huanggai Town（6 962.93 kg/ha）and Hekou Town（7 083.79 kg/ha）.Correlation analysis further validated these results：seed cotton yield showed the strongest correlation with the number of bolls per plant（Huanggai Town：r=0.98；Hekou Town：r=1.00），followed by boll weight（Huanggai Town：r=0.93；Hekou Town：r=0.94）. In summary，appropriately delayed sowing（June 4）combined with timely chemical topping（July 9）can optimize plant population structure，improve photosynthetic performance，and balance source⁃sink relationships，thereby achieving high yields and efficiency in summer⁃sown short⁃season cotton. This represents a suitable simplified cultivation model for cotton⁃growing areas in the Yangtze River Basin.

Key words: Summer?sown short?season cotton, Sowing date, Chemical topping, Population structure, Photosynthetic characteristics, Yield, Synergistic effect

摘要： 为明确播期与化学打顶时间配置对夏播短季棉群体结构优化、光合效率提升与产量形成的协同调控机制，构建长江流域适宜的轻简化高效栽培模式，于2024年在湖南省临澧县合口镇和临湘市黄盖镇开展一年两点的田间试验，以早熟棉品种湘农早1号为材料，采用双因素随机区组试验设计，设置3个播期［5月25日（S1）、5月30日（S2）、6月4日（S3）］和4个化学打顶时间［6月25日（T1）、7月2日（T2）、7月9日（T3）、7月16日（T4）］，系统测定群体结构、光合特性和产量形成等指标。结果表明，播期、化学打顶时间及其互作对夏播短季棉群体结构、光合特性和产量形成均产生显著影响。其中，6月4日播种配合7月9日打顶处理（S3T3）的综合表现最优：叶面积指数控制在2.45~2.60，单株干物质积累量较S1T1处理分别提高17.5%（黄盖镇）和22.8%（合口镇），冠层光合有效辐射分别提高44.5%（黄盖镇）和27.9%（合口镇），净光合速率分别提高64.4%（黄盖镇）和75.1%（合口镇）；产量构成方面，S3T3处理较其余各处理均能实现成铃数和铃质量的协同提高，从而实现黄盖镇（6 962.93 kg/hm²）和合口镇（7 083.79 kg/hm²）两地最优的籽棉产量表现。相关性分析进一步验证了上述结果：籽棉产量与单株铃数相关性最强（黄盖镇r=0.98，合口镇r=1.00），其次是单铃质量（黄盖镇r=0.93，合口镇r=0.94）。综上，适当晚播（6月4日）配合适时化学打顶（7月9日）能够优化群体结构、改善光合性能、协调源库关系，实现夏播短季棉的高产高效，是长江流域棉区适宜的轻简化栽培技术模式。

关键词: 夏播短季棉, 播期, 化学打顶, 群体结构, 光合性能, 产量, 协同效应