Research progress on the applicability of saline water irrigation for ameliorating coastal saline-alkali land

The efficient utilization of coastal saline-alkali land is crucial for ensuring food security and improving the ecological environment in China. Although freshwater scarcity and soil salinization pose dual challenges, abundant saline water presents opportunities for sustainable agricultural production in this area. However, long-term use of saline water irrigation may result in a series of adverse effects. Therefore, this study systematically reviews the effects of saline water irrigation on the soil, crops, and ecological environment of coastal saline-alkali land. It comprehensively reviews key technologies such as saline water quality improvement, safe and efficient irrigation, and stepwise utilization of fresh and saline water. Innovatively, it condenses and expounds on three models: the composite ecological model of salt-tolerant crops with saline water irrigation, the comprehensive management model for saline water irrigation and water-salt regulation, and the synergistic model of photovoltaic-edible fungi-saline water. Considering the characteristics of water-salt distribution, precipitation, and the water table in coastal saline-alkali areas, a zoned utilization strategy for saline water is proposed. In severely saline-alkali areas, pioneer halophytes, such as Suaeda glauca and Tamarix chinensis, are planted. Saline water (with a salinity greater than 5 g∙L⁻¹) is mainly used for irrigation. Freeze-thaw technology is employed to reduce salt accumulation in the 0–40 cm soil layer over the main root zone. Depending on local conditions, either the “saline water drip irrigation + high ridge + film mulching” model is selected or the rotation model of edible fungi and vegetables is implemented. In moderately saline-alkali areas, salt-tolerant cash crops, such as cotton and forage grass, are cultivated. Brackish water (with a salinity of 2−5 g∙L⁻¹) is primarily used, with fresh water supplementation during the salt-sensitive growth stages of crops (such as the seedling and bud stages of cotton). Water activation treatment and the stepwise utilization technology of fresh and saline waters are applied. Additionally, the synergistic model of photovoltaic-edible fungi-saline water can be adopted to enhance sustainability. In lightly saline-alkali areas, moderately sensitive and moderately salt-tolerant food crops, such as maize and wheat, are grown. Fresh water is mainly used for irrigation, with brackish water supplemented during the salt-tolerant growth stages (e.g., the grain filling stage of wheat and large bell-mouth stage of maize). The smart irrigation scheduling approach, based on the plant water deficit index, precisely controls the irrigation volume and time for fresh and brackish water in accordance with soil water, salt, and crop growth conditions, thereby optimizing water use efficiency. Future research should focus on strengthening the studies on the impact of saline water irrigation on regional water resources and salt balance, deepening the simulation of regional water-salt movement models, and exploring mechanisms and strategies for the synergistic development of saline water irrigation and ecosystems. Moreover, further studies should promote the integration of multiple technologies and smart management to provide a theoretical foundation and technical support for the sustainable development of China’s coastal saline-alkali land.