Winter irrigation affected the movement of soil moisture, temperature, and salt, which was an effective improvement measure widely used in seasonal freeze–thaw areas. In this paper, we investigated the effects of different salinized cotton fields (mild salinization (S1), 5.15 g·kg⁻¹; moderate salinization (S2), 8.17 g·kg⁻¹; severe salinization (S3), 11.15 g·kg⁻¹) and different winter irrigation rates (W0, 0 m³·hm^-2; W1, 3000 m³·hm^-2; W2, 3600 m³·hm^-2; W3, 4200 m³·hm^-2) on soil moisture, temperature, salinity, and cotton growth in seasonal freeze–thaw areas. The results showed that the winter irrigation affected the temporal and spatial dynamics of soil moisture, temperature, and salinity, and the winter irrigation rate and degree of soil salinization were significantly correlated with soil moisture, temperature, and salinity (p < 0.01). Winter irrigation stabilized the soil temperature and reduced the freeze–thaw index of the soil. The heat conservation effect of winter irrigation increased with increasing winter irrigation rate and salinization degree, with the greatest effect on the freezing index of S2 and on the thawing index of S3. The soil water content and total salt concentration before spring tillage were significantly correlated with winter irrigation rate and degree of soil salinization (p < 0.05), and when the winter irrigation quota of different salinized cotton fields was greater than 3600 m³·hm^-2, the moisture content of soil layer 0–100cm increased by more than 20%, and the desalination reached over 40%, compared with the values before winter irrigation. Winter irrigation improved the emergence rate and yield of cotton, with the soil salinization degree being significantly negatively correlated and winter irrigation rate significantly positively correlated with the emergence rate and yield of cotton fields in the following year (p < 0.01). Compared with the control treatment without winter irrigation, the average increases in cotton yield were W3 (53.32%) > W2 (45.00%) > W1 (29.36%). There was no significant difference in seedling emergence rate or yield between slightly and moderately salinized cotton fields under high winter irrigation rates (W2 and W3) (p > 0.05), although the seedling emergence rate and yield of severely salinized cotton fields increased significantly with increasing winter irrigation rate. In conclusion, winter irrigation proved to be a valuable treatment for severely salinized cotton fields, and the results of this study allowed us to determine the optimal winter irrigation rate for saline alkali cotton fields.

Cotton is the most important cash crop in Xinjiang but low utilization rate of water and fertilizer is restricting healthy development of this industry. At present, there is a lack of water and nitrogen management optimization methods based on multi-objectives of cotton water use efficiency (WUE), nitrogen use efficiency (NUE), yield, and income. A continuous field experiment was conducted during 2017–2018 to study the effects of water–nitrogen coupling on cotton growth, WUE, NUE, nitrogen partial factor productivity, yield, quality, and economic benefits under drip irrigation in northern Xinjiang. Using multiple regression and spatial analyses, the water and nitrogen management strategy for multi-objective optimization was determined. Three irrigation levels were used—low (I₁), medium (I₂), and full (I₃)—Representing 75%, 87.5%, and 100% of cotton water demand, respectively. The three nitrogen application levels were low (N₁, 210 kg/ha), medium (N₂, 280 kg/ha), and high (N₃, 350 kg/ha), representing 75%, 100%, and 125% of the local nitrogen application, respectively. Among all treatments, the leaf area index, boll weight, dry matter quantity and yield reached respective maxima of 4.43 m²/m², 4.73 g, 16,623 kg/ha, and 6333 kg/ha for the I₃N₂ treatment. Cotton fiber quality was the best for I₃ irrigation, but too little or too much nitrogen reduced fiber quality. The economic benefit under I₃ irrigation was 1.93–4.81 times that for I₁. For a single optimization objective, WUE reached a maximum of 1.78 kg/ha·mm for irrigation of 415.80 mm and nitrogen application of 295.71 kg/ha; corresponding single maxima follow: NUE of 37.65% for 418.27 mm and 278.57 kg/ha; yield of 6416.42 kg/ha for 470.12 mm and 304.29 kg/ha; and economic benefit of 15,338.55 RMB/ha for 470.12 mm and 307.14 kg/ha. Multiple regression and spatial analysis showed that for irrigation of 430.71–440.12 mm and nitrogen application of 270.95–318.45 kg/ha, the WUE, NUE, yield, and economic benefits of cotton simultaneously exceeded 90% of their maxima, which was an efficient and reasonable water and nitrogen management mode in this location. The results provide a scientific basis for effective integrated management of water and fertilizer in drip irrigation cotton fields in northern Xinjiang.

Bio-organic fertilizers have demonstrated significant potential in enhancing saline-alkali soil properties, boosting crop yield, and reducing chemical fertilizer dependency. However, the extent of improvement and optimal application rates for varying saline-alkali soil conditions remain unclear. We conducted a 2-year field experiment (2022–2023) to evaluate the effects of different bio-organic fertilizer application rates on soil properties, nutrient availability, and cotton yield across three saline-alkali cotton fields with varying salinity levels 4.58, 9.07, and 12.76 g·kg⁻¹ (T1-T3). Four treatments were implemented, involving chemical fertilizer reductions of 0% (CK), 20% (F1), 40% (F2), and 60% (F3). Results indicated that, compared to CK, bio-organic fertilizer application reduced soil bulk density, salinity, and pH by an average of 15.84%, 53.86%, and 7.5%, respectively. Concurrently, soil moisture content, organic matter, nitrogen, phosphorus, potassium, and cotton yield increased by 36.72%, 58.4%, 59.4%, 77.9%, 88.7%, and 50.32%, respectively. Notably, the improvements in soil properties and cotton yield were more pronounced in 2023 compared to 2022. Principal component analysis revealed that a 60% bio-organic fertilizer application rate was optimal for mild, moderate, and severely salinized cotton fields. These findings provide a scientific basis for reducing chemical fertilizer use while improving the productivity and sustainability of saline-alkali soils.

To explore the potential of smashing ridge tillage irrigation, it is necessary to investigate how smashing ridge tillage technology with mulched drip irrigation affects soil water, salinity, and cotton yield in saline fields. We conducted a two-year (2020–2021) field experiment to study the effects of different smashing ridge tillage depths on soil bulk density, moisture, salinity, dry matter production, yield, and its constituents (effective bolls, 100-bell weight). There were three smashing ridge tillage depths: A (20 cm), B (40 cm), and C (60 cm), with traditional tillage as the CT. The results showed that all of the smashing ridge tillage could reduce soil bulk density, improve the utilization and uptake of deep soil water during the rapid growth period, and reduce the soil salt content. Compared with the CT treatment, the average soil bulk density of the 0–60 cm soil layer in treatments A, B, and C in 2020 and 2021 decreased by 3.05%, 5.87%, 10.09%, and 1.65%, 4.48%, and 8.49%, respectively. The average soil water content in the 0–120 cm soil layer at the flowering and boll stage decreased by 3.68%, 6.28%, 9.04%, and 3.59%, 6.52%, and 9.98%, respectively; the soil salt content in the 0–120 cm soil layer at the boll opening stage decreased by 4.21%, 6.75%, 11.95%, and 5.47%, 24.25%, and 54.13%, respectively. Cotton dry matter production and yield tended to increase with an increasing depth of smash ridge tillage. Treatment C obtained the maximum dry matter production, seed cotton yield, effective bolls, and 100-boll weight. The dry matter production at the boll opening stage was significantly increased by 17.16% and 15.91%, and the yield was significantly increased by 65.24% and 84.14% in treatments C in 2020 and 2021, respectively, compared to CT. The smashing ridge tillage of 60 cm can optimize the structure of the soil tillage layer and also reduce soil salinity and increase yield, which is the suitable depth of smashing ridge tillage for saline cotton fields in the south of Xinjiang. The findings of the study can provide some theoretical basis and practical experience for the improvement of saline soils and sustainable agricultural development in South Xinjiang, China.