Elsevier

Field Crops Research

Volume 275, 1 January 2022, 108337
Field Crops Research

Plant topping effects on growth, yield, and earliness of field-grown cotton as mediated by plant density and ecological conditions

https://doi.org/10.1016/j.fcr.2021.108337Get rights and content

Highlights

  • Manual topping increased cotton yield regardless of plant densities and ecological conditions relative to non-topping.

  • Chemical topping decreased yield at low plant density relative to non-topping because of greater biomass reduction.

  • Chemical topping increased cotton yield at moderate and high plant densities via greater assimilates partitioning to fruits.

  • Chemical topping could replace manual topping at moderate and high plant densities without ecological dependence.

Abstract

Manual removal of the main-stem growth tip is traditionally used to break the apical dominance of cotton (Gossypium hirsutum L.). Chemical topping with plant growth regulators also effectively inhibits apical dominance. However, the effect of chemical topping on yield increases and whether plant density or ecological conditions affect its efficacy are unclear. Therefore, a three-year field experiment with a split-plot design was conducted to determine the effects of plant topping, plant density, and their interactions on cotton yield and related physiological and agronomical parameters at three sites with different ecological conditions in China. In each site, the main plots were assigned low, moderate, or high plant density and the subplots were assigned no topping, manual topping, or chemical topping. Growth, yield, yield components, earliness, and late-season leaf photosynthesis as well as labor and material inputs were examined each year. Compared with no topping, both chemical and manual topping greatly reduced plant height at all sites. Manual topping increased seed cotton yield and earliness in all tested plant densities and sites. However, plant density but not ecological condition greatly mediated the effect of chemical topping on yield. At low plant density, the yields with chemical topping were 4–6% lower than those with no topping and 5.5–10.8% lower than those with manual topping at the three sites. Although yields with chemical topping were comparable with those of manual topping at moderate and high plant densities, they were 8.6–12.8% higher at moderate density and 13.8–16.4% higher at high plant density than those with no topping across years and sites. Averaged across the sites, chemical topping reduced biological yield by 12.7% at low plant density. Although biological yield decreased slightly, chemical and manual topping increased the harvest index by 12.4% and 13.3% at moderate density and by 15.6% and 17.4% at high density, respectively. In comparison with no topping, the reduction in seed cotton yield with chemical topping at low plant density was attributed to insufficient biological yield, whereas the increase in yield at moderate and high plant densities was mainly due to greater partitioning of assimilates to reproductive tissues. Compared with manual topping, chemical topping produced 23.2% lower net returns as a result of lower seed cotton yield at low plant density but produced 8.1% and 20.9% higher net returns at moderate and high plant densities, respectively, because of savings in labor inputs and comparable seed cotton yields. In addition, chemical topping increased the earliness percentage compared with that of no topping. Overall, this study demonstrates that chemical topping is a promising alternative to traditional manual topping under moderate or high cotton plant density.

Introduction

Cotton (Gossypium hirsutum L.) owns an indeterminate growth habit with strong apical dominance. Manual removal of the main-stem growth tip (manual topping) has been widely adopted in China and other cotton-growing countries with abundant agricultural labor (Dai and Dong, 2014) because it effectively breaks apical dominance and increases the partitioning of assimilates to reproductive organs, leading to more squares, flowers, bolls, and lint yield (Hosny et al., 1995, Li et al., 2006). However, manual topping is labor intensive, and meeting labor needs has become a great challenge because rural laborers are increasingly migrating to cities and towns to work in secondary and tertiary industries in the rapid urbanization of China, greatly reducing both the quantity and quality of rural labor (Dai et al., 2017a). Therefore, the development of a new plant topping method that is not labor-based to replace manual topping has attracted great attention.

Chemical topping may be a promising alternative that uses plant growth regulators to inhibit apical dominance in crop plants (Ren et al., 2013, Rosolem et al., 2013, Siebert and Stewart, 2006). Research on chemical topping has been conducted since the 1960s (Cathey et al., 1966, Sill and Nelson, 1970, Su et al., 2012, Uhring, 1971, Zhu et al., 2020). Chemical suckercides are used to control axillary shoot growth and to maximize yield in tomato (Gianfagna et al., 1998, Logendra et al., 2004), red pepper (Kim and Ho, 1980), and tobacco (Mahmood et al., 2007, Taylor et al., 2008). They also effectively inhibit sucker formation and repress the expression of genes in auxin and cytokinin signaling pathways that are involved in axillary shoot formation in tobacco (Singh et al., 2015). Chemical topping with plant growth regulators has also been used in cotton. Kang et al. (2015) found that chemical topping reduces plant height and number of fruiting branches, shortens the length of fruiting branches and petiole from internode 1 to internode 6, and increases the yield compared with non-topping. Similar increases in lint yield and yield components with chemical topping compared with non-topping are reported in full-season cotton under single cropping (Li et al., 2018, Ren et al., 2013) and in short-season cotton under double cropping (Liu et al., 2019, Yu et al., 2021). There are other benefits of chemical topping in cotton, including reduced labor inputs (Dong et al., 2017a), improved seed quality (Ge et al., 2015), and compacted plant type (Zhao et al., 2019, Zhu et al., 2020). However, according to the study of Ye et al. (2017), although chemical topping increased the number of lower and inner within-plant bolls, it did not increase boll weight, yield, or lint percentage compared with those with manual topping or non-topping. In our previous research, yield decreased with chemical topping compared with manual topping under low plant density (Dong, 2019). The differences in chemical topping efficacy suggest that it may be affected by other factors (Liu et al., 2019, Ye et al., 2017). Therefore, the factors that influence the effects of chemical topping in cotton need to be identified and studied.

Application of plant growth regulators, such as mepiquat chloride, to regulate plant growth and development has long been widely adopted in cotton (Li et al., 1991). The effect of mepiquat chloride can vary with plant density (Dong, 2019, Zhao et al., 2019) and ecological conditions (Rosolem et al., 2013, Ye et al., 2017). Therefore, we hypothesized that the efficacy of chemical topping is also mediated by planting density and ecological condition. These factors may be the most important reasons for the differences in chemical topping effects reported previously. Thus, we conducted a three-year field experiment with a split-plot design with plant density as the main plot treatment and plant-topping mode as the subplot treatment in different ecological regions of China to study the effects of plant topping. The objectives of the study were to determine a) the effects of plant topping, planting density, and ecological condition on seed cotton yield and net return; b) whether plant density or ecological condition mediated the efficacy of plant topping. This study will further expand the application of plant growth regulators in cotton production, which has important significance or reference for China and other cotton-producing countries in the world.

Section snippets

Experimental site and cultivar

Field experiments were conducted in three sites with different ecological conditions (Table S1) in China from 2016 to 2018. Site 1 was in Hutubi County (44°68′N, 87°12′E) in Xinjiang in the Northwest inland cotton-growing region. The experimental area is in a warm-temperate arid zone and has a continental climate. The average annual precipitation is 184.2 mm, the frost-free crop growth season is 165 d, and evaporation is 1850 mm. Annual effective accumulated temperature is 3443 °C. Xinluzao 64,

Yield, yield components, and earliness

Seed cotton yield was affected by the interaction between topping mode and plant density in each experimental site, but the interaction was not affected by experimental year (Table 1, Table 2, Table 3). Averaged across the three years, at low plant density, chemical topping reduced seed cotton yield by 4% at site 1, 4.7% at site 2, and 6% at site 3 compared with no topping and by 10.8% at site 1, 5.5% at site 2, and 8.6% at site 3 compared with manual topping. By contrast, at moderate and high

Discussion

In this study, manual topping increased seed cotton yield and earliness compared with no topping regardless of plant density or ecological region. More importantly, chemical topping also increased seed cotton yield and earliness at moderate and high plant densities, although not at low plant density, indicating that plant density mediated the effects of chemical topping. This study also provides new academic insights into how plant topping improves seed cotton yield through regulating

Conclusions

Manual and chemical topping increased seed cotton yield compared with no topping at moderate and high plant densities regardless of ecological conditions, attributing to increased partitioning of assimilates into reproductive tissues. Although manual topping increased seed cotton yield at low plant density, chemical topping decreased yield because of greater reductions in biological yield than those with no topping. Thus, plant density mediated the effect of chemical topping. Although seed

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was financially supported by the National Key Research and Development Program of China (2020YFD1001002), National Natural Science Foundation of China (31771718, 31801307), China Agricultural Research System (CARS-15-15), Seed-Industrialized Development Program in Shandong Province (2020LZGC002), Agricultural Scientific and Technological Innovation Project of Shandong Academy of Agricultural Sciences (CXGC2021A06).

References (56)

  • H.M. Cathey et al.

    Chemical pruning of plant

    Science

    (1966)
  • Cotton Research Institute (CRI)

    Chinese Academy of Agricultural Sciences

    Cultivation of Cotton in China

    (2013)
  • Y.N. Cui et al.

    Effects of three topping methods on cotton plant type structure and yield at different density

    Xinjiang Agric. Sci.

    (2018)
  • Y.N. Cui et al.

    Effect of combining cotton artificial detopping with chemical detopping on cotton agronomic and yield traits

    Xinjiang Agric. Sci.

    (2020)
  • Dai, J.L., Dong, H.Z., Eneji, A.E., Li, W.J., Zhang, D.M., Tang, W., 2019. A cotton cultivation method with chemical...
  • H.Z. Dong

    Light and Efficient Cultivation with Concentrated Maturation in Cotton

    (2019)
  • H.Z. Dong et al.

    Effects of cotton root stock on endogenous cytokinins and abscisic acid in xylem sap and leaves in relation to leaf senescence

    J. Exp. Bot.

    (2008)
  • H.Z. Dong et al.

    Key technologies for light and simplified cultivation of cotton and their eco-physiological mechanisms

    Acta Agron. Sin.

    (2017)
  • H.Z. Dong et al.

    New grouped harvesting-based population structures of cotton

    Sci. Agric. Sin.

    (2018)
  • J.J. Dong et al.

    Review of light and simplified cotton cultivation technology in the Yellow River valley

    Sci. Agric. Sin.

    (2017)
  • M.I.M. El-Shahawy

    Attempts to control excessive vegetative growth of cotton

    Egypt. J. Agric. Res.

    (2000)
  • J. Ge et al.

    The cotton seed endosperm germination under different detopping biochemicals

    Xinjiang Agric. Sci.

    (2015)
  • T.J. Gianfagna et al.

    Improving tomato harvest index by controlling crop height and side shoot production

    Life Support Biosph. Sci.

    (1998)
  • A.A. Hosny et al.

    Prediction of optimum density and row spacing for cotton in different regions of Egypt

    Ann. Agric. Sci.

    (1995)
  • Z.H. Kang et al.

    Effects on the agronomic and economic characters of cotton by applying different topping chemicals

    Xinjiang Agric. Sci.

    (2015)
  • H.K. Kim et al.

    Effect of planting density and chemical pinching of axillary buds with MH treatment on yield of red pepper

    Horticult. Environ. Biotechnol.

    (1980)
  • F. Li et al.

    Effects of chemical topping with fortified mepiquat chloride on cotton growth, yield and maturity under different plant densities and nitrogen rates in the Yellow River valley region of China

    J. China Agric. Univ.

    (2018)
  • F. Li et al.

    Applied research of cotton chemical topping agent in Hunan

    China Cotton

    (2016)
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