Cotton Genomics and Genetics 2025, Vol.16, No.2, 57-71 http://cropscipublisher.com/index.php/cgg 63 5 Effects on Cotton Yield and Fiber Quality 5.1 Yield under different irrigation systems Irrigation system is one of the important factors that determine the yield of cotton seed cotton. Sufficient and uniform irrigation can meet the water demand of cotton throughout the growth process, thereby realizing the yield potential; on the contrary, unreasonable irrigation (whether insufficient or excessive) will lead to reduced yield. A large number of studies have compared the effects of different irrigation modes and water management on cotton yield. In general, the treatment with efficient irrigation technology and water supply according to the law of crop water demand has the highest yield. For example, in an experiment in Baotai, Shihezi (northern Xinjiang), the seed cotton yield of the treatment with full irrigation under film drip irrigation increased by more than 10% compared with traditional furrow irrigation (Li et al., 2009). The effect of deficit irrigation on cotton yield depends on the degree and period of water deficit. Mild deficit often has no obvious effect on yield; Lin et al. (2024) reported that the yield of mild deficit (90% irrigation) treatment was the same as that of full irrigation, showing the advantage of water saving without reducing yield. However, as the degree of water deficit increases, the number of bolls per cotton plant and the boll weight both decrease, and the yield is significantly reduced. In the study of Rao et al. (2016), severe water deficit treatment (only 50% irrigation) resulted in a 17% reduction in seed cotton yield compared with full irrigation. Irrigation frequency also affects yield performance: high-frequency small-water irrigation is conducive to avoiding drought stress, maintaining stable growth, and often has higher yields; low-frequency large-water irrigation may cause drought stress between two irrigations, and yield is slightly affected (Yu et al., 2011). Jia et al. (2024) found in a three-year experiment in southern Xinjiang that the seed cotton yield of high irrigation volume (420 mm seasonal total) treatment was 2.5%-7.5% higher than that of medium irrigation volume (370 mm), and high frequency (once every 4 days) was slightly better than low frequency (every 12 days). In areas with water shortages, moderately sacrificing a certain yield in exchange for substantial water savings may be a realistic option. For example, a comprehensive analysis by Ouda et al. (2024) showed that compared with full irrigation, implementing an irrigation deficit of about 20% can save 20% of water while only reducing cotton yield by 5%. Therefore, in production, the irrigation system should be selected according to the water resource status and economic trade-offs: if the water source is sufficient and the goal is to maximize the yield, sufficient irrigation combined with drip irrigation and other efficient methods can be adopted; if the water source is limited, the deficit irrigation strategy is adopted to control the yield loss to the minimum through fine management. Regardless of the strategy, it is proved that scientific irrigation plays a decisive role in the high and stable yield of cotton. 5.2 Influence of cotton lint quality and fiber strength Irrigation not only affects the yield of cotton, but also has an important impact on the quality of cotton fiber. Cotton fiber quality includes indicators such as length, fineness (micronaire value), specific strength, and maturity. These characteristics depend to a large extent on the water and nutrient supply during cotton growth. The study of Nazar et al. (2012) showed that moderately sufficient and balanced water supply can help improve fiber quality; on the contrary, water stress may cause the fiber to become shorter, thicker, and the strength to decrease. In the process of post-flowering development, cotton fiber needs continuous water to support cell elongation and cellulose deposition. If drought occurs during the flowering and boll-setting period, the fiber cell elongation period is shortened, and the final fiber length is reduced. At the same time, the cell wall of the fiber is not fully developed under water stress, and the maturity and strength are also affected. Analysis of irrigation experiments in cotton fields in Xinjiang shows that increasing the amount of irrigation and appropriately increasing the frequency of irrigation are beneficial to improving fiber quality. The specific strength of cotton fibers in high irrigation treatments increased significantly, and the micronaire value (reflecting fineness and maturity) decreased, indicating that the fibers were more slender and matured uniformly; while the fiber strength of low irrigation treatments was low, the micronaire value increased, and the proportion of coarse and short fibers increased. In addition, compared with low-frequency irrigation, high-frequency irrigation increased the average length of cotton fibers by about 0.5 mm, increased the specific strength at break, and improved the quality (Jia et al., 2024). Another study on different irrigation strategies also found that the length and strength of cotton fibers decreased under water shortage conditions, but if the lower limit of irrigation was reasonably controlled (such as the relative
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