Cotton Genomics and Genetics 2025, Vol.16, No.2, 57-71 http://cropscipublisher.com/index.php/cgg 66 which is a macro-environmental problem faced by cotton fields in many arid areas. Implementing scientific irrigation and improving water use efficiency can reduce the adverse impact on the water environment while meeting agricultural needs. Secondly, irrigation methods affect soil salinity dynamics. In arid areas, soil salt is prone to accumulate on the surface due to evaporation and concentration, threatening cotton growth. Reasonable irrigation should not only supplement leaching to prevent salt accumulation, but also prevent excessive leaching from causing water waste. Wu et al. (2020) proposed a soil salinity threshold that cotton can tolerate, and suggested that the root zone salinity be maintained within the acceptable range for crops by controlling the irrigation volume, thereby achieving water-salt balance. For cotton fields that have already been salinized, concentrated irrigation can be used to wash away salt in early spring or during the fallow period, and then the irrigation volume can be finely controlled during the growing period to balance salt suppression and water conservation (Feng et al., 2021). Thirdly, mulch film residue pollution is a new environmental problem brought about by the large-scale application of drip irrigation under film. Traditional PE mulch film is difficult to completely recycle, and some residual film remains in the soil every year. As farming continues year after year, it accumulates and causes the physical and chemical properties of the soil to deteriorate. Residual mulch film will hinder soil water and air permeability, inhibit root growth, and may also adsorb pesticides and fertilizers to cause secondary soil pollution. It is reported that the amount of residual film in the tillage layer of some cotton fields in Xinjiang that have been irrigated with drip irrigation under film for a long time has exceeded 20 kg/mu, affecting both soil bulk density and water holding capacity (Zhang et al., 2019). To this end, it is necessary to strengthen the management of residual film and promote alternatives such as degradable mulch films. 7 Case Study: Irrigation Practices in Xinjiang, China 7.1 Regional overview and importance of cotton planting Xinjiang Uygur Autonomous Region is the largest cotton producing region in China, ranking first in the country in terms of planting area, total output and yield per unit area. According to the Xinjiang Statistical Yearbook (2023), Xinjiang's cotton planting area is stable at around 37 million mu, accounting for about 80% of the country. Its natural conditions of drought, little rain and abundant sunshine are conducive to cotton growth, but also cause a high degree of dependence on irrigation. In order to achieve high and stable yields, Xinjiang took the lead in promoting sub-film drip irrigation technology on a large scale in the country, becoming one of the largest water-saving irrigation areas in the world (Wang et al., 2008). This technology not only changed the traditional way of water resource utilization, but also reshaped the water use pattern of cotton planting. 7.2 Implementation of drip irrigation under plastic cover The sub-film drip irrigation system used in Xinjiang cotton fields usually consists of a water supply main, capillary tubes, drip irrigation belts, ground film and control valves. The water source is mostly surface water or groundwater, which is transported to the field through a pressurized system. Mulching with plastic film helps reduce soil evaporation, increase soil temperature, and inhibit weed growth. Drip tapes are buried in the furrows, with one tape per ridge or two rows per tape. Farmers use timers or smart irrigation systems to accurately irrigate according to the cotton growth stage. Under this mode, the cotton yield per unit of water is greatly increased. According to Jia et al. (2024), in the three-year experimental field of drip irrigation under plastic film in southern Xinjiang, the average water saving rate reached 30%, and the seed cotton yield increased by 12%-18% compared with traditional furrow irrigation. Drip irrigation under plastic film can also realize the integrated supply of water and fertilizer, dissolving fertilizer in water and transporting it to the vicinity of the root system, improving fertilizer utilization efficiency and reducing loss (Figure 2) (Yin et al., 2010). 7.3 Results: yield increase, water saving and challenges Drip irrigation under plastic film has greatly improved the water use efficiency and yield of cotton fields in Xinjiang. Sheng et al. (2014) showed in Shihezi area in northern Xinjiang that the IWUE of cotton fields irrigated with drip irrigation under plastic film was 2.8 kg/m³, which was 47% higher than that of traditional furrow irrigation. In addition, this technology significantly reduces the problem of soil salt accumulation caused by irrigation, which is conducive to maintaining the root zone ecology. However, the system also has some challenges: first, the residual film under the film is seriously polluted, posing a threat to the physical and chemical
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