The cotton variety used in this study is the locally predominant cultivar Xinluzhong 54. The experiment was conducted from 2024 to 2025 in Shaya County, Xinjiang (41°17′N, 82°42′E, elevation 897 meters). This region features a warm temperate continental arid climate, with an annual average precipitation of 47.3 mm, annual evaporation of 2000.7 mm, annual sunshine duration of 3031.2 hours, and an annual average temperature of 10.7 °C. The highest recorded temperature reached 30.9 °C, while the lowest dropped to -13.7 °C. The frost-free period spans 214 days. Daily minimum/maximum temperatures and precipitation during the study period are shown in Figure 1. The experimental site consists of sandy loam soil. In 2024, the soil’s initial moisture content was 16.13%, salt content was 3.98 g/kg, total nitrogen content was 0.65 g/kg, bulk density was 1.51 g/cm³, and pH was 8.26. In 2025, the initial moisture content was 14.38%, salt content was 4.16 g/kg, total nitrogen content was 0.63 g/kg, bulk density was 1.54 g/cm³, and pH was 8.45.

This study employed a split-plot design, with the main plots assigned two irrigation frequencies (P1: Day 1 after sowing; P2: Day 1 + Day 8 after sowing) and the subplots assigned three irrigation volumes (W1: 15 mm, W2: 30 mm, W3: 45 mm). Irrigation was completed in a single application for P1 and divided equally into two applications for P2. The widely adopted production practice of a single 30 mm irrigation (P1W2) served as the control treatment. A total of six treatments were established, each replicated three times. Cotton was cultivated using a 1-film, 3-pipe, 6-row planting pattern. The plastic mulch width was 2.05 meters, with alternating row spacing (64 cm + 12 cm). Patch-type drip tape was laid in the narrow rows at a flow rate of 2.1 L/h. Each experimental plot covered three film widths, measuring 6.67 m × 10 m. To prevent water seepage between adjacent treatment zones, a 1-meter buffer zone was established between each treatment. Sowing dates were April 7, 2024, and April 9, 2025. Irrigation water sourced from local canal water had a mineralization degree of 0.79 g·L^-1 in 2024 and 0.83 g·L^-1 in 2025. Irrigation was conducted within one day after sowing. Detailed irrigation protocols are provided in Table 1, the plot layout diagram and sampling locations in Figure 2.

Data were organised and calculated using Excel 2023. Analysis of variance (ANOVA), Pearson correlation analysis, and linear fitting were performed using SPSS 2024. Plotting was conducted using Origin 2024 and Surfer 15.0.

Both irrigation frequency and irrigation volume exerted significant effects on soil moisture content in cotton fields (Figure 3, P<0.05). Findings indicate that soil moisture content in 2024 increased by 2.46% compared to 2025. Results from both years demonstrate that, under identical irrigation volumes, increasing irrigation frequency significantly elevates average soil moisture content. Compared with the P1 treatment, the P2 treatment increased soil moisture content by 6.22% to 8.62%. At the same irrigation frequency, average soil moisture content showed an upward trend with increasing irrigation volume. Under P1 conditions, the average soil moisture content of the W3 treatment increased by 5.83% and 3.79% compared with W2 and W1, respectively. Under P2 conditions, the W3 treatment exhibited soil moisture content 2.68% and 3.49% higher than W2 and W1 respectively. Under the synergistic regulation of irrigation frequency and volume, the P2W3 treatment achieved the highest average soil moisture content over two years, exceeding other treatments by 3.28% to 12.37%.

Further analysis of the spatiotemporal distribution of soil moisture revealed (Figures 4, 5) that irrigation volume and frequency significantly influenced soil moisture in the 0–20 cm soil layer. Vertically, soil moisture content in the 0–20 cm layer was markedly higher than in the 20–60 cm layer. On days 6 and 12 post-sowing, the W3 treatment exhibited average increases in soil moisture content within the 0–20 cm layer of 15.26% and 35.38% compared to W2, and 12.99% and 32.08% compared to W1, respectively. Horizontally, soil moisture content at 0 cm from the dripper (narrow row spacing) was significantly higher than at 30 cm (wide row spacing), with this difference gradually diminishing as irrigation volume and frequency increased. Specifically, on days 6 and 12 post-sowing, under identical irrigation frequency, soil moisture content at 30 cm horizontally in the W3 treatment was on average 14.72% and 32.87% higher than in W2 and W1 respectively. Under the combined regulation of irrigation frequency and volume, at 6 days post-sowing, the soil moisture content at 30 cm horizontally and 20 cm vertically from the dripper in the P2W3 treatment was 21.93% lower than that in P1W3. However, at 12 days post-sowing, the soil moisture content in the P2W3 treatment was 6.73% higher horizontally and 5.48% higher vertically than that in P1W3.

The results over the past two years indicate: Both irrigation volume and irrigation frequency exerted significant effects on copper content in the 0–20 cm soil layer (Table 2, P<0.05). At identical irrigation volumes, increasing irrigation frequency markedly enhanced soil moisture uniformity at 10 and 12 days post-sowing. Specifically, under treatment P2, Cu levels in the 0–20 cm soil layer at 10 and 12 days post-sowing increased by 1.05%–3.26% and 1.04%–2.08%, respectively, compared to treatment P1. At constant irrigation frequency, increasing irrigation volume also enhanced moisture uniformity. Under P1 conditions, the Cu value in the 0–20 cm soil layer for the W3 treatment was 5.83% and 3.79% higher than that of W2 and W1, respectively. Under P2 conditions, the Cu value in soil moisture content for the W3 treatment was 2.68% and 3.49% higher than that of W2 and W1, respectively. When both factors were jointly regulated, the P2W3 treatment yielded the optimal results: at 10 and 12 days post-sowing, the Cu values in the 0–20 cm soil layer reached 0.95 and 0.98, respectively, representing increases of 3.49% to 12.41% compared to other treatments.

Both irrigation frequency and irrigation volume exerted significant effects on soil salinisation in cotton fields (Figure 6, P<0.05). Findings indicate that soil salinity decreased by 5.81% in 2024 compared to 2025. Results from both years demonstrate that increasing irrigation frequency while maintaining constant irrigation volume significantly reduces average soil salinisation levels. Compared with the P1 treatment, soil salinity decreased by 1.66% to 5.23% under the P2 treatment. At the same irrigation frequency, soil salinity showed a decreasing trend with increasing irrigation volume. Under the P1 condition, the W3 treatment reduced soil salinity by 5.73% and 13.27% compared with the W2 and W1 treatments, respectively. Under P2 conditions, the W3 treatment exhibited soil salinity levels 3.78% and 9.29% lower than W2 and W1 respectively. Under the combined effects of irrigation volume and frequency, the P2W3 treatment recorded the lowest average soil salinity over two years, reducing levels by 3.78% to 12.94% compared to other treatments.

Further analysis of the spatial distribution of soil salinity revealed (Figures 7, 8) that irrigation volume and frequency significantly influenced soil salinity in the 0–20 cm soil layer. Vertically, salinity levels in the 0–20 cm layer were markedly lower than those in the 20–60 cm layer. On days 6 and 12 post-sowing, W3 exhibited average reductions in soil salinity within the 0–20 cm layer of 2.21% and 7.36% respectively compared to W2, and 3.27% and 4.19% compared to W1. Horizontally, soil salinity at 0 cm from the dripper (narrow row) was significantly lower than at 30 cm (wide row), with the difference gradually diminishing as irrigation volume and frequency increased. Specifically, on days 6 and 12 post-sowing, under identical irrigation frequency, soil salinity at 30 cm horizontally in W3 was on average 5.53% and 12.35% lower than in W2 and W1 respectively. Under the combined regulation of irrigation frequency and volume, at 6 days post-sowing, the soil salinity at 30 cm horizontally and 20 cm vertically from the dripper in the P2W3 treatment was 7.21% higher than that in P1W3. However, at 12 days post-sowing, the soil salinity in the P2W3 treatment was 11.64% and 9.56% lower than that in P1W3 in the horizontal and vertical directions, respectively.

Both irrigation volume and irrigation frequency significantly influenced soil salinity in the 0–20 cm soil layer (Table 3, P<0.05). At identical irrigation volumes, increasing irrigation frequency markedly reduced soil salinity uniformity in the 0–20 cm layer at 9 and 12 days post-sowing. Compared to the P1 treatment, the P2 treatment exhibited reductions in Cu content within the 0–20 cm soil layer of 8.69–16.66% and 6.59–14.28% at 10 and 12 days post-sowing, respectively. At the same irrigation frequency, increasing irrigation volume reduced soil salinity uniformity in the 0–20 cm layer. Under P1 conditions, the Cu value for soil moisture content in the 0–20 cm layer under treatment W3 decreased by 4.21% and 6.18% compared to W2 and W1, respectively. Under P2 conditions, the Cu content in the 0–20 cm soil layer of the W3 treatment was 2.29% and 1.16% lower than that of W2 and W1, respectively. Under the combined regulation of irrigation frequency and volume, the Cu value of soil salinity in the 0–20 cm layer under P2W3 reached 0.84 and 0.85 at 10 and 12 days post-sowing, respectively, representing reductions of 3.49% to 12.41% compared to other treatments.

Both irrigation volume and irrigation frequency significantly influenced the desalination effect on soil salinity in the 0–20 cm soil layer (Table 4, P<0.05). At identical irrigation volumes, the desalination effect in the 0–20 cm soil layer exhibited an upward trend with increasing irrigation frequency, with treatment P2 showing an improvement of 11.62% to 34.79% compared to treatment P1. At constant irrigation frequency, the desalination effect increased incrementally with rising irrigation volume. Under P1 conditions, the W3 treatment exhibited a 12.63% and 8.05% reduction in desalination effectiveness compared to W1 and W2, respectively. Under P2 conditions, the W3 treatment showed a 37.42% and 7.28% decrease relative to W1 and W2. Under the combined effects of irrigation volume and frequency, at DAS 12, the P2W2 treatment achieved a 48.06% reduction in salinity in the 0–20 cm soil layer. This represented a 6.78% improvement over the P2W3 treatment and a 20.17%–35.34% increase compared to other treatments.

Both irrigation volume and frequency significantly influenced cotton seedling emergence rates (Figure 9). Findings revealed that the average germination rate in 2024 exceeded that of 2025 by 1.59%. Results from both years indicate that, at constant irrigation volume, increasing irrigation frequency tends to enhance emergence rates. Compared to the P1 treatment, the P2 treatment showed emergence rate increases ranging from 8.84% to 19.95%. Data from both years demonstrate that, at constant irrigation frequency, cotton seedling emergence rates initially rise then decline with increasing irrigation volume. The W2 treatment exhibited a germination rate 2.91% higher than W1 and 12.41% higher than W3. Under the synergistic effect of irrigation volume and frequency, the P2W2 treatment achieved an average germination rate of 90.63% over two years, surpassing other treatments by 5.79% to 13.91%.

By analysing the relationship between soil water-salt distribution characteristics and cotton seedling emergence rate (Figure 10), it was found that soil salinity in the 0–20 cm layer exhibited a significant negative correlation with cotton seedling emergence rate (p<0.05). Conversely, soil moisture content, moisture uniformity, salinity uniformity, and desalination rate in the 0–20 cm layer showed significant positive correlations with cotton seedling emergence rate (p<0.05). In the 20–40 cm soil layer, soil salinity, moisture content, moisture uniformity, salinity uniformity, and desalination rate showed no correlation with cotton emergence rate (p>0.05).

Further analysis revealed a significant non-linear relationship (R²>0.83) between soil salinity and moisture content in the 0–20 cm layer and cotton emergence rate (Figure 11). Emergence rate initially increased with rising soil salinity and moisture content before declining. The desalination efficiency and uniformity of water distribution in the 0–20 cm soil layer showed a significant positive linear correlation with cotton emergence rate (R²>0.82). Conversely, the uniformity of soil salinity distribution exhibited a significant negative linear correlation with cotton emergence rate (R²=0.83).

Irrigation strategies are the dominant factors regulating soil water migration (Xu et al., 2017; An et al., 2025). Moderately increasing irrigation volume extends both vertical and horizontal water penetration distances, maintains sustained moisture in the surface soil layer, and expands the wetted area, thereby enhancing water distribution uniformity (Feng et al., 2023; Sampathkumar et al., 2012). Under the synergistic regulation of irrigation volume and frequency, a high-frequency, low-volume irrigation pattern helps retain more water in the upper root zone. Soil moisture content gradually decreases with increasing distance from the drip tape (Zalacáin et al., 2019). Higher irrigation volumes can slow the rate of soil moisture decline and improve water distribution uniformity (Wang et al., 2006; Qi et al., 2020). Under the conditions of this study, both irrigation rate and frequency during seedling emergence significantly influenced soil moisture migration and distribution patterns. Increasing irrigation frequency while moderately reducing irrigation rate effectively maintained soil moisture content in the 0–20 cm layer and enhanced uniformity of soil moisture distribution. This finding aligns with the conclusions of (Tian et al., 2022). Compared to other treatments, the P2W2 treatment increased soil moisture content by 2.86%–12.05% in the 0–20 cm soil layer and improved moisture uniformity by 3.14%–11.82%. Additionally, this study found that under “dry sowing and wet emergence” conditions, when irrigation volume reached 20 mm during seedling emergence, further increasing irrigation volume enhanced horizontal diffusion of the wetting front while reducing vertical infiltration range. Soil moisture content at the 0–30 cm horizontal depth increased by 6.37% in the P2W3 treatment group compared to the P2W2 group. The migration pattern of the wetting front during irrigation is jointly regulated by irrigation volume and initial soil conditions; increasing irrigation volume promotes its horizontal development (Han et al., 2025). The phenomenon observed in this study may stem from increased irrigation raising the soil matric potential, causing downward flow velocity to lag behind lateral transport rates. This disruption of the equilibrium between downward seepage and matric potential ultimately enhances the horizontal expansion of soil moisture content, a phenomenon consistent with both theoretical and observational findings on unsaturated flow in soil (Cote et al., 2003; Hu et al., 2025).

Irrigation volume determines the depth of salt leaching, while irrigation frequency influences the distribution of salts; together, they regulate the distribution characteristics of soil salinity (Du et al., 2023; Liu et al., 2025a). Under “dry sowing and wet emergence” conditions, lower irrigation volumes readily exacerbate surface salt accumulation due to increased surface evaporation, thereby intensifying soil salinization (Sun et al., 2019). Moderately increasing irrigation volume can extend the diffusion range of the wetting front, thereby promoting the leaching of surface salts and enhancing desalination in the topsoil (Guan et al., 2013). The frequency of irrigation plays a particularly crucial role in regulating salt redistribution patterns, as it fundamentally alters the dynamic equilibrium between water movement and evaporation processes (Chen et al., 2018). High-frequency irrigation maintains elevated soil matric potential in the root zone, not only directly promoting downward salt migration with water flow but more importantly, continuously suppressing surface salt accumulation caused by surface water evaporation. This effectively prevents salt accumulation in the seed germination layer or the primary root zone of crops (Wieber et al., 2025). In contrast, although low-frequency irrigation involves larger single-application volumes and can generate significant leaching effects in the short term post-irrigation, intense soil surface evaporation during extended irrigation intervals rapidly reverses the direction of salt movement. This process causes salts leached into deeper soil layers to migrate back upward with water, accumulating at the soil surface and ultimately forming salt crusts or salt patches that impede seedling emergence (Ding et al., 2024). Thus, irrigation frequency essentially regulates the cycle of vertical leaching- upwelling dynamics in the soil profile. Under this mechanism, high-frequency irrigation effectively enhances stable leaching of salts within the root zone by avoiding deep percolation caused by single excessive irrigation events (Gao et al., 2025). Under the conditions of this study, irrigation volume and frequency significantly influenced soil salinity migration and distribution characteristics. Increasing both irrigation volume and frequency effectively leached salts to the 30–40 cm soil layer, reduced soil salinity content and uniformity in the 0–20 cm layer, and enhanced desalination efficacy. Compared to other treatments, the P2W2 regimen enhanced soil salinity reduction in the 0–20 cm layer by 20.17%–35.34%, decreased salinity content by 3.78%–12.94%, and reduced salinity distribution uniformity by 3.49%–12.41%. Previous studies predominantly advocated that ‘high frequency + high irrigation volume’ yielded optimal desalination effects. However, this research observed during the cotton emergence stage in “dry sowing and wet emergence” fields that employing high-frequency irrigation combined with a 30% reduction in irrigation volume achieved 48.06% desalination in the 0–20 cm soil layer. representing a 6.78% increase over the ‘high frequency + high irrigation volume’ approach and exceeding other treatments by 20.17% to 35.34%. This discrepancy may stem from excessive irrigation in the W3 treatment causing partial water percolation into deeper layers, preventing adequate dissolution of salts within the 0–20 cm profile and hindering their migration to deeper zones. This reduced salt leaching efficiency in the 0–20 cm soil layer (Liu et al., 2025b). Conversely, the P2W2 combination achieved precise regulation of soil water and salts through ‘moderate irrigation volume + high frequency’, better meeting the requirements for controlling surface soil salinity during the seedling stage of cotton fields.

The soil water-salt environment directly influences the emergence process of cotton seedlings, with an appropriate water-salt environment promoting seedling emergence (Tao et al., 2023). Under “dry sowing and wet emergence” conditions, irrigation volume and frequency are key factors regulating soil water-salt distribution patterns. Insufficient irrigation volume leads to inadequate salt leaching, exacerbating surface salt accumulation and elevating soil osmotic pressure. High-salinity stress not only hinders seed water uptake but, according to prior research, also disrupts normal seed metabolic initiation through ionic toxicity and osmotic stress, significantly reducing emergence rates (Terletskaya et al., 2023). Conversely, excessive irrigation leads to overly high soil moisture content, resulting in deteriorated root zone aeration. Soil hypoxia severely impairs seed aerobic respiration and energy supply, similarly reducing cotton seedling emergence rates (Lu et al., 2023). Through the synergistic effects of irrigation volume and frequency, this approach prevents both salt stress caused by water deficiency and soil degradation induced by waterlogging (Ertek et al., 2004). This pattern establishes an optimal water-salt environment in the root zone, creating favorable soil conditions for cotton seed germination and emergence, thereby significantly improving seedling emergence rates (Ma et al., 2017; Li et al., 2021). Through rational adjustment of irrigation volume and frequency, the P2W2 treatment demonstrated the following improvements compared to other treatments: soil moisture content in the 0–20 cm layer increased by 2.86%–12.05%, soil salinity decreased by 3.78%–12.94%, soil moisture distribution uniformity improved by 3.14%–11.82%, and increased salt leaching efficiency by 20.17% to 35.34%. Consequently, cotton emergence rates were 5.79% to 13.91% higher than in other treatments, this result is consistent with previous studies, which indicate that creating suitable and uniform water-salt conditions in the germination layer through irrigation management is a key physiological process for ensuring uniform crop emergence and improving emergence rates (Guang et al., 2019). Moreover, the emergence rate in 2024 was 1.84% higher than that in 2025 (Figure 9), which may be attributed to the poorer emergence conditions in 2025 due to frequent rainfall and lower temperatures during the germination period (Wang et al., 2025). Furthermore, this study found that beyond 20 mm of irrigation, continued increases in irrigation volume actually led to a declining trend in cotton seedling emergence rates. This phenomenon may stem from excessive soil moisture content when irrigation volume and frequency exceed specific thresholds, resulting in deteriorated soil aeration. This, in turn, triggers soil compaction that inhibits seed germination metabolism, ultimately reducing emergence rates (Garg et al., 2021). This study elucidates the effects of irrigation frequency and volume on soil water and salt distribution characteristics during the cotton emergence period under dry sowing and wet emergence conditions. Future research may focus on investigating the dynamic changes in physiological indicators of cotton under varying water-salinity conditions, further elucidating the physiological mechanisms underlying irrigation strategy regulation of seedling emergence. By integrating numerical modeling to simulate soil water-salinity transport processes under different irrigation strategies, this approach aims to optimize irrigation schemes for areas with varying degrees of salinization in southern Xinjiang, thereby providing scientific support for the sustainable development of the local cotton industry.