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.

Hami, Xinjiang, is located in an extremely arid region and jujube is the main economic crop. It is important to adopt dwarf and close-planting technology under drip irrigation and to optimize water and fertilizer management to improve jujube yield and quality. Local 12-year-old jujube trees were treated using two factors of irrigation and fertilization. Three irrigation amounts (520, 700, and 880 mm) and three fertilization levels (248, 318, and 388 kg/hm²) were set up in plot experiments. The root system, yield, and quality of jujube were monitored under different irrigation and nitrogen application combinations. The effects on water use efficiency (WUE), nitrogen partial factor productivity (PNP), and economic benefit were analyzed. The water and fertilizer coupling effect of dwarf closely planted jujube was studied by combining multiple regression and spatial analyses. The yield, quality, economic benefits, WUE, and PNP of jujube were significantly affected by irrigation and fertilization. Multiple regression and spatial analyses showed that the highest yield was for irrigation of 700 mm and a nitrogen rate of 340 kg/hm². For the maximum net benefit, irrigation was 806 mm and nitrogen was 388 kg/hm²; correspondingly, for the highest total sugar, values were 688 mm and 362 kg/hm²; for vitamin C, they were 622 mm and 376 kg/hm²; for PNP, they were 880 mm and 256.57 kg/hm²; and for WUE, they were 520 mm and 388 kg/hm². A comprehensive evaluation of each index showed that the acceptable irrigation amount for yield, quality, WUE, and net benefit of ≥85% of the maximum value was 600–628 mm, and the nitrogen application rate was 360–372 kg/hm². This study provides guidance for the scientific management of water and fertilizer in the drip irrigation and fertilization process of local jujube trees.

With the popularization and development of drip irrigation under film, the problem of secondary soil salinization in Xinjiang is becoming more and more serious. To explore water and salt transport in drip irrigation under mulch and drainpipe drainage, drainage tests of drainage ditches in saline-alkali soil in the Xinjiang 112 group were used to monitor soil salinity changes by controlling field irrigation. Then, a HYDRUS (PC-Progress, Prague, Czech Republic) numerical model was used to simulate and analyze the changes in salinity during cotton growth and the autumn salt return stage in saline-alkali soil under drainage conditions. The agreement between the simulated and measured values was high, and the model parameters were reliable. During the growth period of cotton, the salinity continued to decrease, and the salt began to return after the harvest. Compared with before planting, in the 0–80 cm soil layer, the average desalinization rate reached 43.52% under the mulching films, and the average desalinization rate reached 13.83% under and between the mulching films. After the cotton was harvested, salt returned to the upper layer of soil. However, it still showed a decrease compared with the level before sowing. The average salt content of 0–80 cm soil decreased by 5.14%, and the average salt content of 0–200 cm decreased by 2.60%. This shows that the total salt content in soil will continue to decrease after long-term use of drip irrigation and underground pipe drainage.