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

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