In order to optimize the water and nitrogen management mode and realize the efficient scale production of sweet pepper, from 2021 to 2022, field experiments on sweet pepper cultivation with different water and nitrogen coupling modes were conducted in the Hexi Oasis irrigation areas. The regulation effects of the water–nitrogen coupling mode on the dry matter accumulation characteristics, photosynthesis, yield, and water–nitrogen utilization efficiency of sweet pepper were further discussed. Irrigation was set for full irrigation (W1, 75–85% FC [field capacity]), mild (W2, 65–75% FC), and moderate (W3, 55–65% FC) water deficit levels. Three levels of nitrogen were applied, high (N1, 300 kg·ha⁻¹), medium (N2, 225 kg·ha⁻¹) and low (N3, 150 kg·ha⁻¹), with full irrigation and no nitrogen application used as the control (CK). The results showed that the appropriate water–nitrogen coupling mode could enhance the photosynthetic rate, increase dry matter accumulation and the accumulation rate, advance the days of a maximum rate of dry matter accumulation, and improve yield and water–nitrogen utilization efficiency. N1W1 had the greatest dry matter accumulation, the mean rate and the maximum increase rate of dry matter accumulation in sweet pepper, which was not a significant difference from N2W2, but significantly increased by 19.61%, 19.67%, and 23.45%, respectively, compared with CK. Water deficit significantly advanced the days of a maximum rate of dry matter accumulation. The days of a maximum rate of dry matter accumulation appeared 1.18–5.79 days earlier at W3 than at W2 and W1, and the maximum rate appeared gradually later with increasing irrigation. The net photosynthetic rate, the transpiration rate, and stomatal conductance of N2W2 sweet pepper showed the best performance at all growth stages, significantly increasing by 23.87%, 27.71%, and 27.39%, respectively, compared with CK. Moreover, the Intercellular CO₂ concentration was significantly reduced by 14.77% in N2W2 compared to CK. The N2W2 had the highest yield, water use efficiency, and irrigation water use efficiency of sweet pepper, significantly increasing 26.89%, 33.74%, and 31.22% compared to CK. Excessive water and nitrogen dosage reduced nitrogen partial factor productivity, while an appropriate increase in irrigation under reduced nitrogen conditions facilitated the water nitrogen potential. Passage path analysis further showed that water–nitrogen coupling promotes plant biomass formation and distribution by increasing photosynthetic assimilation capacity, ultimately increasing yield. Therefore, the N2W2 treatment (65–75% FC, 225 kg·ha⁻¹) is the ideal water and nitrogen mode for obtaining higher yields and water and nitrogen use efficiency of sweet pepper in a cold and arid environment.

Residual film pollution and excessive nitrogen fertilizer have become limiting factors for agricultural development. To investigate the feasibility of replacing conventional plastic film with biodegradable plastic film in cold and arid environments under nitrogen application conditions, field experiments were conducted from 2021 to 2022 with plastic film covering (including degradable plastic film (D) and ordinary plastic film (P)) combined with nitrogen fertilizer 0 (N0), 160 (N1), 320 (N2), and 480 (N3) kg·ha⁻¹. The results showed no significant difference (p > 0.05) in dry matter accumulation, photosynthetic gas exchange parameters, soil enzyme activity, or yield of spring maize under degradable plastic film cover compared to ordinary plastic film cover. Nitrogen fertilizer is the main factor limiting the growth of spring maize. The above-ground and root biomass showed a trend of increasing and then decreasing with the increase in nitrogen application level. Increasing nitrogen fertilizer can also improve the photosynthetic gas exchange parameters of leaves, maintain soil enzyme activity, and reduce soil pH. Under the nitrogen application level of N2, the yield of degradable plastic film and ordinary plastic film coverage increased by 3.74~42.50% and 2.05~40.02%, respectively. At the same time, it can also improve water use efficiency and irrigation water use efficiency, but it will reduce nitrogen fertilizer partial productivity and nitrogen fertilizer agronomic use efficiency. Using multiple indicators to evaluate the effect of plastic film mulching combined with nitrogen fertilizer on the comprehensive growth of spring maize, it was found that the DN2 treatment had the best complete growth of maize, which was the best model for achieving stable yield and income increase and green development of spring maize in cold and cool irrigation areas.

In order to explore the water and fertilizer requirements of eggplants in the western oasis of the river, the experiment was conducted in Minle County of Gansu Province in 2022 and 2023 under three water stress gradients and three nitrogen application levels: (1) moderate water stress (W₁, 50–60% in field water capacity [FC]), mild water stress (W₂, 60–70% in FC), and full irrigation (W₃, 70–80% in FC); (2) low nitrogen (N₁, 215 kg·ha⁻¹), medium nitrogen (N₂, 270 kg·ha⁻¹), and high nitrogen (N₃, 325 kg·ha⁻¹). Moderate and mild water stress were applied during eggplant flowering and fruiting while full irrigation was provided during the other growth stages; a control class (CK) was established with full irrigation throughout the whole plant growth without nitrogen application. This study investigated the effects of water-saving and nitrogen reduction on the yield, quality, and water-nitrogen use efficiency of eggplants in a cold and arid environment in the Hexi Oasis irrigation area of China. Using the EWM-TOPSIS model, we evaluated different water-nitrogen treatments and determined the optimal irrigation-nitrogen application model for eggplants in this region. The results showed that the W₂N₂ treatment had the highest yield, which was not significantly (p > 0.05) different from the W₃N₂ treatment while significantly (p < 0.05) 35.06% higher than CK in 2022 and 36.91% higher in 2023. In the W₂N₂ treatment, the transverse diameter of eggplants, as well as the contents of soluble protein, soluble sugar, soluble solids, and vitamin C, were all the highest. The W₂N₂ treatment had the maximum water use efficiency and irrigation water use efficiency, which were significantly higher than other water and nitrogen application treatments and CK by 14.79–42.51% in 2022 and 8.79–44.88% in 2023, and 15.86–45.55% in 2022 and 4.68–40.22% in 2023, respectively. By employing the EWM-TOPSIS model for comprehensive evaluation, the results indicated that mild water deficit (60–70% in FC) and moderate nitrogen application (270 kg·ha⁻¹) at flowering and fruiting of eggplants was the optimal water and nitrogen application mode under mulched drip irrigation in the Hexi region of northwest China. The results will provide some theoretical basis for water-saving, productive, high-quality, and high-efficiency cultivation of eggplant in cold and arid environments.

Against the background of increasingly scarce water resources and intensifying water use conflicts, achieving the scientific and optimized allocation of water resources has become crucial to ensuring regional sustainable development. Based on the traditional water resource optimization models that consider social, economic, and ecological objectives, this study introduces a spatial equilibrium level as a fourth optimization objective, constructing a multi-objective water resource allocation optimization model. The model simultaneously incorporates constraints on water supply, water demand, and decision variable non-negativity, as well as coupling coordination constraints among the water resources, socio-economic, and ecological subsystems within each water use unit. The NSGA-III algorithm is employed to obtain the Pareto front solution set for the four objectives, followed by a comprehensive ranking of the Pareto solutions using an entropy-weighted TOPSIS method. The solution exhibiting the best trade-off among the four objectives is selected as the decision basis for the water allocation scheme. Taking Jiuquan, Jiayuguan, and Zhangye cities in western Gansu Province as the study area, the results indicate that the optimal allocation scheme can guide the cities to shift from “water-deficit usage” toward “water-saving usage,” achieving a reasonable balance between meeting water demand and water conservation requirements. This promotes coordinated development among the water resource, socio-economic, and ecological subsystems within each city as well as among the cities themselves, thereby facilitating sustainable utilization of water resources and sustainable development of socio-economics and the ecological environment. The findings can serve as a reference for water resource allocation strategies in the study region.

The grain-filling process is a key stage in ensuring a high yield of maize. Nitrogen is one of the nutrient elements most essential for maize, especially in cold and arid areas. To evaluate the effects of plastic-film mulching and nitrogen application on the maize grain-filling process, the impact of different plastic-film mulching (degradable plastic film, J; common plastic-film mulching, P) and nitrogen fertilizer levels (0 kg·ha⁻¹, N0; 160 kg·ha⁻¹, N1; 320 kg·ha⁻¹, N2; 480 kg·ha⁻¹, N3) on maize grain-filling characteristic parameters and final 100-kernel weight were tested in 2021 and 2022. The results showed that the interaction between film mulching and nitrogen application significantly (p < 0.05) affected the filling characteristic parameters and final 100-kernel weight of maize. The final 100-kernel weight was highest at the N2 nitrogen application level, which was 7.69–38.13% higher under degradable plastic-film mulching and 3.17–38.06% higher under common plastic-film mulching than at other levels. The nitrogen application level significantly (p < 0.05) increased grain-filling duration and rate. The duration time in reaching the maximum grain-filling rate under the N2 nitrogen application level was around 1.1967–5.7835 d under degradable plastic-film mulching and 2.8688–8.1704 d under the common plastic-film mulching, with the maximum and average grain-filling rate increased by 0.0595–0.2063 g·d⁻¹ and 0.0447–0.1423 g·d⁻¹ under degradable film mulching and 0.1418–0.3058 g·d⁻¹ and 0.1082–0.2125 g·d⁻¹ under common film mulching, respectively. The nitrogen application levels of N2 and N3 under two plastic-film mulching methods prolonged the duration of the rapid and slow increase period of grain filling and increased the grain-filling rate and the average rate. The average grain-filling rate at the N2 level increased by 0.0469–0.1759 g·d⁻¹ and 0.0090–0.0454 g·d⁻¹ under degradable film mulching and 0.1113–0.2581 g·d⁻¹ and 0.0203–0.0648 g·d⁻¹ under common film mulching, respectively. Therefore, common plastic film mainly prolonged the duration of the gradual increase period of grain filling and increased the grain-filling rate; meanwhile, the effect of degraded plastic film on the grain-filling rate increase and prolonging of the grain-filling duration was gradually highlighted during the rapid and the slow period of increase. In addition, the 320 kg·ha⁻¹ of nitrogen application level under both common plastic-film mulching and degradable-film mulching was more conducive to prolonging the grain-filling duration of maize, which increased the grain-filling rate and 100-kernel weight, laying a foundation for a high yield of maize.

Increasing planting density is an effective strategy for improving maize (Zea mays L.) productivity, but it can also intensify interplant competition and canopy shading. Enhanced nitrogen application may help offset these negative effects. A two-year field experiment was conducted in the Hexi Corridor, an arid region of northwestern China, using a full factorial design with three planting density levels D1 (75,000 plants ha⁻¹), D2 (90,000 plants ha⁻¹), and D3 (105,000 plants ha⁻¹), and three nitrogen application levels N1 (198 kg ha⁻¹), N2 (264 kg ha⁻¹), and N3 (330 kg ha⁻¹). The aim was to clarify how the interaction between planting density and nitrogen application regulates maize canopy structure and affects resource use efficiency in arid areas. The results showed that planting density, nitrogen rate, and their interaction significantly affected canopy structure, photosynthetic traits, grain yield, and water and nitrogen use efficiency. From the perspective of each growth stage, combinations of medium and high planting density and nitrogen application levels facilitated the optimization of maize canopy structure, promoted plant growth and dry matter accumulation, and elevated leaf SPAD values. Meanwhile, treatment D2N2 exhibited the most prominent improvement in maize yield components, with grain yield increased by 1.44–35.58% on average across experimental years. This treatment also sustained superior water and nitrogen use efficiency, achieving an average water use efficiency of 3.53 kg·m⁻³ and an average partial factor productivity of nitrogen of 53.41 kg·kg⁻¹. Comprehensive multi-index evaluation verified that D2N2 represented the optimal cultivation regime. This regime could reduce nitrogen fertilizer input by 20% while fully exploiting light and heat resources inherent to arid regions. Collectively, this study establishes a viable green and high-efficiency cultivation paradigm for maize production with high yield, reduced fertilizer input and water conservation, and delivers critical theoretical and technical references for the sustainable intensification of maize cultivation in arid regions of northwest China.