Background: Cotton production in China is challenged by high labor input including manual topping (MT ). Recently, to replace MT in the Xinjiang cotton region of China, mepiquat chloride (MC) was applied once more than the traditional multiple-application; this was designated as chemical topping (CT), but it is unclear whether the amount of irrigation needs to be adjusted to accommodate CT. Results: The main plots were assigned to three drip irrigation amounts [300 -(I1), 480 -(I2), and 660 -(I3) mm], and the subplots were assigned to the CT treatments [450 -(MC1), 750 -(MC2), and 1050 -(MC3) mL·hm?225％ MC] with MT as a control that was performed after early bloom. The optimum drip irrigation amount for CT was explored based on leaf photosynthesis, chlorophyll fluorescence, biomass accumulation, and yield. There were significant influences of drip irrigation, topping treatments and their interaction on chlorophyll fluorescence characteristics, gas exchange param-eters and biomass accumulation characteristics as well as yield. The combination of I-2 and -MC2 -(I2MC2) performed best. Compared with -I2MT, the net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and photochemical quenching coefficient (qP) of I-2MC2 significantly increased by 4.0％～7.2％, 6.8％～17.1％, 5.2％～17.6％, and 4.8％～9.6％, respectively, from the peak flowering to boll opening stages. Moreover, I-2MC2 showed fast reproduc-tive organ biomass accumulation and the highest seed cotton yield; the latter was 6.6％～12.8％ higher than that of -I2MT. Further analysis revealed that a 25％ MC emulsion in water -(MCEW) application resulted in yield improvement by increasing Pn, φPSII, and qP to promote biomass accumulation and transport to reproductive organs. Conclusion: The results showed that the 480 mm drip irrigation combined with 750 mL·hm?2 MC increased the rate of dry matter accumulation in reproductive organs by increasing Pn, φPSII, and qP to improve photosynthetic perfor-mance, thus achieving higher yield.

TIAN Yu;LIAO Baopeng;HAN Huanyong;WANG Fangyong;DU Mingwei;TIAN Xiaoli;LI Zhaohu

Xinjiang Academy of Agricultural and Reclamation Science,Shihezi 832003,Xinjiang,China;College of Agron-omy,Shihezi University,Shihezi 832000,Xinjiang,China;College of Agronomy/Crop Chemical Control Research Center,China Agricultural University,Beijing 100193,China

棉花研究（英文）

[1]TIAN Yu;LIAO Baopeng;HAN Huanyong;WANG Fangyong;DU Mingwei;TIAN Xiaoli;LI Zhaohu-.The efficacy of chemical topping in field?grown cotton is mediated by drip irrigation amount in irrigated agricultural area)[J].棉花研究（英文）,2022(02):59-70

I2MC2,I2MT,2MC2,MCEW

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