Cotton Genomics and Genetics 2025, Vol.16, No.2, 57-71 http://cropscipublisher.com/index.php/cgg 58 This study aims to systematically review the research progress on the effects of cotton irrigation strategies on its growth, yield and fiber quality in the past five years. The focus was on the water demand of cotton at different growth stages, the effects of water stress and over-irrigation on cotton physiology and ecology; the classification and comparison of traditional and advanced irrigation technologies, especially the application of sub-film drip irrigation and other technologies in arid areas; the mechanism of the influence of irrigation system on cotton growth parameters (root system, plant height, canopy development, flowering and boll formation); the influence of different irrigation methods on cotton final yield and fiber quality; water use efficiency and sustainability issues of water-saving irrigation; and the results and experience of large-scale application of sub-film drip irrigation in Xinjiang, China. This study summarizes the key experience of efficient cotton irrigation and proposes future research and practice innovation directions, in order to provide a reference for sustainable cotton production in arid areas. 2 Overview of Cotton Water Requirements 2.1 Cotton growth stages and their specific water requirements The entire growth cycle of cotton includes the seedling stage, vegetative growth stage (before budding), reproductive growth stage (flowering and boll formation stage) and boll opening and maturity stage, and the water requirements in different stages vary significantly. In the seedling and bud stages, cotton water requirements are relatively low, and excessive water may lead to shallow root development and leggy growth; in the mid-summer when flowering and boll formation occurs, cotton plants reach the maximum leaf area and heavy boll load, and evapotranspiration rises rapidly at this time, reaching 542 mm, accounting for 88% of the total transpiration water loss, which is the peak water requirement throughout the year (Figure 1) (Zhao et al., 2023). Hussain et al. (2020) showed that under sufficient irrigation conditions, the total water requirement of cotton during the entire growth period is approximately between 500-800 mm depending on the regional climate. For example, in the cooler climate of the eastern cotton region of the North China Plain, the seasonal water requirement is about 620-670 mm, while in the hot Mediterranean climate the seasonal water requirement is higher (Yang et al., 2021). Usually, cotton is most sensitive to water and has the greatest demand for water from budding to flowering and in full bloom and boll formation, requiring timely and sufficient water supply; while the requirements for water are relatively low during the sowing and seedling stage and the end of boll opening. Based on this water demand law, phased water supply is often adopted in irrigation practice, with irrigation strengthened during the critical growth period and water control appropriately in the late growth period to ensure both yield and improve water use efficiency (Shen et al., 2012). The water consumption characteristics of cotton at each stage lay the scientific foundation for formulating a phased irrigation system. 2.2 Effects of water shortage and overwatering on cotton physiology Water stress directly affects the physiological process and growth vitality of cotton. When the available soil water is lower than the cotton water requirement, the plant's stomatal conductance decreases, the photosynthesis rate decreases, the relative water content and chlorophyll content of the leaves decrease, and the plant growth is hindered (Luo et al., 2016). Mild to moderate drought stress first inhibits the growth of cotton stems and leaves and the development of flower buds. Severe drought will lead to increased shedding of young buds and flowers. Shareef et al. (2018) showed that drought stress reduced plant height and leaf area, and caused a decrease in photosynthesis rate under increased water deficit. Under moderate drought, photosynthesis decreased by about 30%, growth traits decreased by more than 20%, and significantly increased the content of osmotic regulating substances such as proline and abscisic acid to help plants resist water deficit. On the other hand, excessive water (such as long-term soil overwetting or excessive irrigation) can also have an adverse effect on cotton. Excessive irrigation can cause soil hypoxia, inhibit root respiration and deep rooting, and cause "waterlogging" symptoms. Cotton is manifested as yellowing leaves, root rot, and increased bud and boll shedding rates (Yan et al., 2009). An overly humid environment can also easily induce the occurrence of soil-borne diseases such as cotton wilt, reducing the number of bolls per plant and the yield of cotton. In general, whether it is water shortage or overwatering, it will disrupt the normal physiological metabolic balance of cotton and affect dry matter accumulation and reproductive growth. Therefore, extreme water stress and long-term overhumidity should be
RkJQdWJsaXNoZXIy MjQ4ODYzNA==