Regulations of salt and water of saline-alkali soil: A review

The safety utilization of saline water resources guarantees sustainable development of agricultural production in the Low Plain near the Bohai Sea. Focusing on water shortage and soil salinity, a series studies were conducted on reclamation of saline soils and regulation of water and salt transportation in the farmlands at Nanpi Eco-Agricultural Experimental Station of Chinese Academy of Sciences, where is a typical site of saline and water deficit regions in the North China Plain. This paper reviewed the study results of the development process for reclamation of saline soil and regulation of water and salt transfer in the farmland. Before the 1980s, most works in the region focused on reduction of flood risk through building of irrigation and drainage canals. In the 1980s, researches focused on optimal shallow groundwater regulation, saline soil utilization and water-saving technologies in the farmland with the aim of resolving actual agricultural production problems in saline soil areas. The researchers proposed threshold values for shallow groundwater table with no secondary salinization and developed irrigation scheme for winter wheat. In the 1990s, researches on the mechanisms and technologies of saline water irrigation were carried out to improve winter wheat grain yield and reduce fresh water utilization in the region. The threshold salinity for saline water irrigation was improved from 3 g·L^-1 to 5 g·L^-1. Meanwhile, researchers explained the reasons for the threshold value increase. In recent 10 years, the mechanisms and technological modes of multiple water resources utilization (precipitation collection, safe shallow saline water utilization, reasonable water transfer and water saving) in the farmland was analyzed. The modes included salt tolerant cultivars planting, soil salt transformation technologies, optimal irrigation schedule and organic manure reduction of salt accumulation. According to water quantity and quality, the optimal irrigation schedule was developed based on the available water resources. This included sufficient irrigation before winter, drought resistant irrigation in spring and emergency irrigation after maize sowing. On the basis of previous studies, an integrated technological mode for multiple water resources was developed. Meanwhile, the "Bohai Granary Demonstration Project of Science and Technology" was implemented, which had significant social, economic and ecological benefits. In future, research work will mainly focus on synergetic promotion of crop quality, quantity, resource use efficiency and green agriculture development based on available water and soil resources and the requirements of the local people. These works provided theoretical and technological basis for sustainable development of localized agriculture in the region.