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BACKGROUND: Cotton (Gossypium hirsutum L.) is the fiber crop most widely cultivated globally and one of the most important commercial crops in China, irrigation is closely related to the growth of cotton. A water temperature for irrigation that is too low or too high inhibits cotton growth. Poor irrigation timing results in water and nutrient deficiencies that reduce cotton yield. Therefore, it is necessary to determine the appropriate irrigation timing and water temperature. METHOD: We conducted an experiment in an arid region of north‐western China to assess the effects of irrigation timing and water temperature on soil temperature and the photosynthetic characteristics, biomass, total nitrogen (N), and seed cotton yield. Two irrigation times (daytime and nighttime) and four water temperatures (15, 20, 25, and 30 °C) were combined into eight treatments. RESULTS: Our results showed that water warming and nighttime irrigation improved the photosynthesis, biomass, N concentration (the proportion of total N weight in the plant biomass, in g kg−1), N content (the mass of total N, in g plant−1), and cotton yield. The optimal water temperature range for photosynthesis was 25.7–28.7 °C. Water warming also boosted the biomass allocation to the stem and increased the N allocation to the stem and leaf. Nighttime irrigation enhanced these phenomena. Water warming also increased the number of bolls per plant but reduced the single boll weight, increasing the seed cotton yield by 5.88–11.46%. At the same water temperature, irrigation during the night increased the number of bolls per plant and the single boll weight, improving the seed cotton yield by 2.95–4.31%. Among them, NI25 (nighttime irrigation with 25 °C water temperature) increased the yield by 14.13–14.90% compared with CK (daytime irrigation with 15 °C water temperature), which offers the best combination for increasing the yield. CONCLUSION: Our study clarifies the optimal irrigation timing and water temperature for cotton production under drip irrigation with film mulching, providing valuable information for improving the cotton yield in arid areas with temperate continental climate. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The sustainable development and utilization of saline-alkali land are closely related to holding fast the minimum cultivated land area of China. The change of soil salt in cotton field under long-term mulched drip irrigation (MDI) is connected with the development of the national cotton industry. From 2015 to 2019, five cotton fields with different applying years of MDI, which were reclaimed in 2004, 2008, 2010, 2012 and 2015 respectively and were saline-alkali wasteland before, were monitored continuously in the Manas River irrigation area of Xinjiang. By means of continuous location monitoring and spatial–temporal variability (For example, the monitoring data of cotton fields under MDI in 2004, 2008, 2010, 2012 and 2015, and in the year of 2015 were counted as 12, 8, 6, 4 and 1 years, respectively), the spatial–temporal variations of soil salt and ions in cotton field with 1-16a MDI technology were presented. The cotton growth characteristics and its main influencing factors were also analyzed in the study. The results showed that saline-alkali cotton field experienced changed from intensive saline soil to moderate saline soil and finally to non-saline soil under long-term MDI. The change of soil salt and the response of cotton growth to soil salt were divided into three typical stages. Firstly, soil desalinated rapidly in 1-4a MDI cotton field, which the annual average desalination rate was 24.93% in 0–100 cm soil layer (root zone). Additionally, the survival rate of cotton rocketed from 1.48% to 42.04%, and yield increased sharply from 72.43 kg ha−1 to 3075.90 kg ha−1. Soil desalination was lower in 5-11a MDI cotton field, which the annual average desalination rate was 10.92% at the root zone. The annual survival rate and yield of cotton increased by 6.26% and 5.18%, respectively. After 12a MDI, the soil salt in cotton field tended to be generally constant, which the average salt content in root zone was less than 2.49 g kg−1. The survival rate of cotton was stable above 90.39%, and the yield per unit area exceeded 5401.32 kg ha−1. Ions, sodium absorption ratio and Cl− and SO42− equivalent ratio (CSER) in cotton soil also decreased with the extension of MDI. Salt composition changed year by year, but the type of intensive saline soil had always been chloride-sulphate solonchak (0.2 < CSER < 1). In practice, with a higher irrigation quota and ideal irrigation water quality, the soil salt environment of saline-alkali soil MDI cotton field had developed in favor of cotton growth in an oasis irrigation area. However, this management practice caused between 124.21–143.61 mm of water resources waste. Therefore, we should further enhanced the consciousness of water-saving and implemented quota management in practice. [ABSTRACT FROM AUTHOR]

• Four biodegradable films were tested to replace PE films in cotton fields under mulched drip irrigation. • Film degradation, soil salinity, residue film accumulation, yield, and WUE were compared. • Degradation process and accumulation of residual film were different between tested films. • Thicker PBAT films and PE films performed similarly in improving cotton yield. • Due to the least accumulation of residual film and highest yield, thicker PBAT films were recommended. To alleviate soil pollution caused by mulching polyethylene (PE) films that are non-degradable and non-recoverable, we evaluated different biodegradable (BD) films (starch-polymer, polybutyrate adipate terephthalate or PBAT, and butylene succinate-co-butylene adipate or PBSA) as alternatives to PE films for mulched drip irrigation in a cotton (Gossypium hirsutum L.) field in Xinjiang, the largest cotton-planting region in China. Film degradation, soil salinity, residue film accumulation, cotton yield, and water use efficiency (WUE) were compared between BD and PE films in two consecutive years (2015–2016). We found that the accumulation of residual film was significantly stronger in plots covered by PE films than by BD films. At the early stage of cotton growth, BD and PE films performed similarly in conserving water in topsoil (0–40 cm depth). Degradation of BD films initiated 40–60 days after sowing. Thus, at the late stage of cotton growth, PE films remained intact and were more effective than BD films in wetting the soil. Due to the drier soil, soil salinity in plots covered by BD films was higher than those by PE films. PBAT films showed a slower degradation process than PBSA and starch films under the mulching condition but degraded more completely after buried in soil. After mulched drip irrigation was managed for two years, cotton yield showed no significant difference between plots with PE films (5722 kg ha−1) and those with thicker PBAT films (5699 kg ha−1). However, mulching PE films resulted in a significantly higher WUE than BD films. Therefore, we suggest thicker PBAT films (with the highest yield and WUE and the lowest accumulation of residual film) as potential alternatives to PE films to improve cotton yield and control soil pollution under mulched drip irrigation. [ABSTRACT FROM AUTHOR]