Abstract: 【Objective】The objective of this study is to investigate the feasibility of cotton chemical topping with mepiquat chloride (1,1-dimethyl-piperidinium chloride, DPC) application in the North of Yellow River Valley of China. 【Method】This study was conducted with GX3, XK4, S126 and XS17 as materials in Hejian city in Hebei province and at Shangzhuang Experimental Station of China Agricultural University in Beijing from 2012 to 2014, consisting of six independent experiments. The chemical topping with DPC application included conventional DPC (98% soluble powder, provided by Jiangsu Runze Agrochemical Co. Ltd.) application alone and the combination of conventional DPC application with fortified DPC (DPC⁺, 25% slow-released emulsion, oil in water, developed by Beijing Agricultural Technology Extension Station and Engineering Research Center of Plant Growth Regulator of China Agricultural University, and provided by Xinjiang Golden Cotton Technology Co., Ltd.) application during flowering and fruiting period. These two strategies were hereafter referred to as DPC and DPC+DPC⁺, respectively. The manual topping accompanied with conventional DPC application was served as control (hereafter referred to as DPC+MT). 【Result】 In 2012 and 2013, characterized by great precipitation during flowering and fruiting period (from July to August), DPC and DPC+DPC+ produced significantly 10.6-12.3 cm higher plant and 5.8-7.9 more sympodials compared with DPC+MT. In 2014, characterized by drought in summer, there were no significant differences in plant height between DPC or DPC+DPC⁺ and DPC+MT, and the number of sympodials of chemical topping only increased by 0-3 relative to control. DPC and DPC+DPC⁺ did not significantly affect cotton yield in all experiments, but a reduced yield of DPC+DPC⁺ was noticed in 2012, companied with the less bolls on the upper sympodials but more bolls on the new sympodials occurred after DPC⁺ application as well as a delay of maturation. In terms of 2013 and 2014, DPC+DPC⁺ showed similar yield and maturation to those of DPC+MT. The application time (from mid-July to the end of July) and doses (varying from 750 to 1 500 mL·hm^-2) of DPC⁺ had no significant effects on both plant architecture and cotton yield. While in case of extending the maturity of late bolls, it should be avoided to use large doses of DPC⁺ at the end of July. Compared with DPC+DPC⁺, the conventional DPC application alone (DPC) showed a weaker control in terms of plant height and the number of sympodials, and possibly had a risk of reduced yield in rainy years or at higher plant density. 【Conclusion】Cotton chemical topping with the application of DPC or DPC+DPC⁺ is basically feasible in the North of Yellow River valley of China. And while make a decision whether applying conventional DPC alone or applying DPC+DPC⁺, the meteorological factor, especially precipitation and plant density should be considered carefully.

Key words: the North of Yellow River valley of China, cotton, mepiquat chloride, chemical topping