Drought and soil salinity are two major limiting factors on the agricultural productivity in arid northwest China. Particularly, 2.96 million hm² of cultivated land is often subjected to the saline-alkali damage, accounting for more than 40 % among the 7.09 million hm² of cultivated land in Xinjiang. The ratio of the agricultural water to total water consumption is more than 90 %, which seriously impacts on the land productivity. The saline water resources have seriously threaten to the large-scale production, due to the soil secondary salinization. However, it is still unclear on the response mechanisms of the soil water-salt dynamics and cotton growth to the salt-drought stress. This study aims to explore the effects of the combined saline-drought stress on the soil water-salt environment, cotton yield, and fiber quality under drip irrigation. The test material was taken as the conventional cotton variety (Xinluzao 42) widely-grown in Xinjiang Province, China. A pot experiment was conducted using a three-factor (initial soil salinity, irrigation amount, and water salinity) and four-level orthogonal design. 16 treatments were set: four initial soil salinity levels (T1: 2 g/kg, T2: 4 g/kg, T3: 6 g/kg, and T4: 8 g/kg), four irrigation volumes (W1: 3375 m³/hm², W2: 3750 m³/hm², W3: 4125 m³/hm², and W4: 4500 m³/hm²), and four irrigation water salinities (S1: 2 g/L, S2: 5 g/L, S3: 8 g/L, and S4: 11 g/L) in Shihezi City, Xinjiang, China, during 2022. A comparison was then conducted to investigate the soil water and salt content, growth and physiology of cotton, as well as seed cotton yield and fiber quality under combined salinity-drought stress after drip irrigation. Their underlying relationships were constructed to integrate the soil water and salt environment with the yield and fiber quality. Correlation analysis, structural equation modeling, and the entropy weight TOPSIS were applied to evaluate the effects of the salt–drought stress on the soil water–salt dynamics and cotton growth. The results showed that soil water content and soil salinity at different cotton growth stages increased with increasing initial soil salinity and irrigation water salinity. With increasing initial soil salinity, cotton plant height, stem diameter, leaf area index, net photosynthetic rate, transpiration rate, stomatal conductance, seed cotton yield, and water use efficiency exhibited decreasing trends. Fiber length initially increased and then decreased, while the uniformity index, breaking strength, elongation, and comprehensive fiber quality index showed fluctuating trends characterized by an initial increase, followed by a decrease and then another increase. In contrast, the micronaire value exhibited an opposite trend. As irrigation water salinity increased, cotton plant height, stem diameter, leaf area index, seed cotton yield, water use efficiency, uniformity index, and breaking strength declined. Fiber length and the comprehensive fiber quality index decreased initially and then increased, whereas the micronaire value and elongation displayed opposite trends.With increasing irrigation quota, plant height, stem diameter, leaf area index, net photosynthetic rate, transpiration rate, stomatal conductance, fiber length, uniformity index, breaking strength, and micronaire value increased initially and then decreased, while seed cotton yield, water use efficiency, and the comprehensive fiber quality index showed increasing trends. Salt–drought stress was altered the soil water–salt environment, thereby resulting on the cotton growth and development. Specifically, there were the negative effects of the soil initial salinity and irrigation water salinity on the cotton growth, photosynthetic properties, yield, water use efficiency, and fiber quality index. While the irrigation amount shared the positive effects on these five factors. Furthermore, the top three optimal treatments were T1W2S2, T1W1S1, and T2W2S1. While the least three treatments were T4W1S4, T3W2S4, and T4W2S3, respectively. These findings can also provide the theoretical reference to increase the cotton yields in the arid regions of Northwest China.

A filter before the pump is one of the most important components in the head of the drip irrigation system. The filter before the pump can be used to preliminarily filter the irrigation water, and then reduce the damage to the pump and the working pressure of the filter system after the pump, finally extending the working duration of the filter system for stable and efficient operation of the drip irrigation system. However, most self-cleaning devices that are driven by motors cannot be interrupted in the filtration process when performing self-cleaning work, leading to the consumption of electric energy. The purpose of this study is to solve the frequent interruption of the filter system for the better self-cleaning performance of the filter before the pump. The Archimedes spiral turbine was applied to combine the hydraulic drive and self-cleaning in the self-cleaning process of the filter before the pump. A systematic investigation was made to explore the influence of blade stride, blade angle, and blade numbers on the rotation speed of Archimedes spiral turbine. A test platform was developed to evaluate the speed of Archimedes spiral turbine when the flow rate was 50-150 m³/h (flow gradient was 25 m³/h). At the same time, a series of simulation tests were carried out on the Archimedes spiral turbine with different parameters by computational fluid dynamics software. The experimental results show that the rotation speed of Archimedes spiral turbine gradually decreased with the increase of the blade stride (or the decrease of the number of single-blade helices), where the reduction amplitude gradually increased. There was a relatively small increase in the rotation speed of Archimedes spiral turbine, with the increase of blade angle and number of blades, whereas, the amplitude continuously decreased. The linear regression showed that the influencing level on the rotation speed was ranked in the descending order of the blade stride, blade angle and blade number. TOPSIS comprehensive evaluation showed that the optimal combination of structural parameters was obtained as follows: blade stride 133 mm, blade angle 90°, and the number of blades 1. The optimal scheme was then introduced into the hydraulic-driven self-cleaning filter before the pump in the self-cleaning test. It was found that the flow rate of the self-cleaning test group was stabilized in the range of 294.9-296.6 m³/h after the initial flow reduction, while the flow reduction was only 1.13%-1.70% when the flow rate was 300 m³/h and the sediment content was 0.9 g/L within 12 h. Better filter cleaning was achieved in the self-cleaning device of a hydraulic-driven Archimedes spiral turbine. The finding can provide a strong reference for the design and optimization of the hydraulic-driven self-cleaning filter before the pump.