Background Although chemical topping agents are now widely used in cotton production, there is a lack of research on screening specialized formulations tailored to the unique ecological conditions of cotton region south of the Tianshan Mountains in Xinjiang. Current reliance on a single-agent application regime often leads to suboptimal efficacy. Given that the root-shoot system is a core determinant of high cotton yields, the underlying mechanism by which chemical topping agents modulate root-shoot coordination remains largely elusive. Methods A two-year field trial was conducted during 2024 and 2025, involving three different chemical topping agents (X1: zifengding agent, X2: paclobutrazol-copper complex, X3: paclobutrazol-zinc complex), manual topping (CK) was conducted as a control. A total of four treatments were included. Results Different chemical topping treatments effectively controlled plant height (PH) and increased number of fruiting branches (NFB) compared to manual topping (CK). It significantly enhanced the net photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr), while reducing intercellular CO 2 concentration (Ci). Compared with the CK treatment, the X1, X2, and X3 treatments increased the boll capacity of the root system(BCR) by 9.40%-9.60%, 15.60%-17.50%, and 20.00%-22.40%, and increased the boll loading of the root system (BLR) by 3.30%-3.80%, 9.80%-10.20%, and 12.40%-14.10%, respectively. Consequently, biomass accumulation peaked under X3 treatment, increasing seed cotton and lint yields by 10.44%-12.17% and 9.20%-11.00%, respectively, while also improving fiber strength. Conclusion This study breaks the extensive “one-size-fits-all” application mode. Specifically, the X3 treatment enables precise and localized application of chemical topping technology, providing theoretical and technical support for high-yield, high-quality, efficient, and green cotton cultivation.
Xiao et al. (2026) studied this question.