Saline water irrigation has become extremely important in arid and semi-arid areas in northwestern China. To study the effect of alternating irrigation models on the soil nutrients, soil salts, and yield of tomatoes with fresh water (total dissolved solids of 0.50 g·L⁻¹) and saline water (total dissolved solids of 3.01 g·L⁻¹), a two-year field experiment was carried out for tomatoes in the Hetao Irrigation District (HID), containing six drip irrigation models: T1 (all freshwater irrigation), T2 (saline water used in the seedling and flowering stages; fresh water in the fruit-set and breaker stages), T3 (saline water in the flowering and fruit-set stages; fresh water in the seedling and breaker stages), T4 (saline water in the fruit-set and breaker stages; fresh water in the seedling and flowering stages), T5 (saline water in the flowering and breaker stages; fresh water in the seedling and fruit-set stages), T6 (saline water in the seedling and fruit-set stages; fresh water in the flowering and breaker stages). The study found that saline water irrigation tends to have a positive effect on soil total nitrogen and a negative influence on soil total phosphorus at each growth stage of the tomato. Soil Na⁺, Mg²⁺, Ca²⁺, K⁺, and Cl⁻ increased over the growth period, soil HCO₃⁻ decreased gradually by growth stage, and the salt ions increased with the amount of saline water applied in alternating irrigation. Though the soil salt accumulated in all experimentally designed alternating irrigation models, soil alkalization did not occur in the tomato root zone under the soil matric potential threshold of −25 kPa. The utilization of saline water resulted in about a 1.9–18.2% decline in fruit yield, but the total soluble solids, lycopene, and sugar in the tomato fruits increased. Ultimately, drip irrigation with fresh water at the seedling to flowering stages and saline water at the fruit-set to breaker stages was suggested for tomato cultivation in HID.

Freshwater shortage is becoming one of the major limiting factors for the sustainable development of agriculture in arid and semi-arid areas of north China. A two-year field experiment about mulched drip irrigation on maize was conducted in Hetao Irrigation District with five irrigation water salinity levels (total dissolved solids; 1, 2, 3, 4, and 5 g·L⁻¹). The effects of irrigation water salinity on maize emergence, growth, yield, grain quality, and soil salt were determined. The results indicated that with the soil matric potential of −20 kPa and irrigation quota for each application of 22.5 mm, the irrigation water salinity showed negative influence on maize emergence and maize morphological characteristics (plant height, leaf area index, stem diameter, and dry matter), as irrigation water salt concentrations exceeded 3 g·L⁻¹. The water use efficiency decreased linearly with the irrigation water salinity raised from 1 g·L⁻¹ to 5 g·L⁻¹, while maize grain protein increased and starch content decreased with the increase of irrigation water salt contents. Additionally, both the vertical radius and horizontal radius of salt isoline by mulched drip irrigation reduced with the irrigation water salt concentrations, when the irrigation water salinity was above 3 g·L⁻¹. Summarily, irrigation water salinity of 3 g·L⁻¹ was recommended for maize mulched drip irrigation in this study.

A field experiment was conducted to test the suitability of growing sunflower under mulched drip irrigation with saline water in the HID (Hetao Irrigation District), North China. The experiment included five planting densities in which the plant spacing was 30, 35, 40, 45, and 50 cm with the same spacing (50 cm) between rows. The results indicated that mulched drip irrigation with saline water was more water-saving than traditional ground irrigation using fresh water, while the irrigation quota increased with the increase of planting density. Little difference of soil salinization was found for the treatments in the 50–100 cm soil layer, which indicated that additional measures should be taken for salt balance with saline water irrigation. The height and leaf area index (LAI) of sunflower increased in response to the increase of plant density, and the head dry matter transferred to the stem at plant densities higher than 47,619 plants/hm². Though the grain weight and 1000-seed weight decreased with increasing plant density, the achene yield and biomass production increased. This research suggests that a plant spacing of 35 cm with 50 cm of row spacing is more suitable for sunflower mulched drip irrigation with saline water at concentrations of 3.0 g∙L⁻¹.

Sustainable development of saline water irrigation was restricted in HID (Hetao Irrigation District) by serious yield reduction and severe salt accumulation without an effective irrigation schedule. Field experiments were carried out to study the effects of drip irrigation thresholds on soil salt transportation and maize yield with shallow saline ground water in 2015 and 2016 in HID. The irrigation was triggered by four soil matric potential (SMP) treatments which measured 20 cm beneath the drip emitter. Results indicate that the shape of the wetting body approximated a one-fourth ellipse on the vertical profile perpendicular to the drip line, while the horizontal radius increased with the increase of SMP. Moreover, salt accumulation decreased with the increasing thresholds in the 0–40-cm layer, while the soil salt in the 40–100 cm layer was hardly affected by SMP thresholds under a drip irrigation quota of 22.5 mm. Maize yield showed a quadratic relationship with the SMP threshold, and the irrigation water use efficiency (IWUE) showed a linear increase in response to the decrease in SMP threshold. Taking into account the salt accumulation, yield and IWUE, a SMP threshold higher than −30 kPa is suggested as the appropriate indicator for maize mulched-drip irrigation with shallow saline groundwater in HID.