Reclamation and utilization of saline soils in water-scarce regions of Bohai Sea

Freshwater scarcity is one of the main constraints to the reclamation of saline soils. Research and demonstration studies on the reclamation and utilization of saline soils in water-scarce regions of Bohai Sea started since 1982 in Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences. The experiments had included regulation of shallow groundwater table via well-water irrigation and rainwater recharge, soil salt leaching via saline water irrigation, root-zone soil desalination via agronomic methods and utilization of halophytes. The major achievements were as follows:1) the regulating levels of shallow groundwater table were determined and the patterns of management by well-water irrigation and rainwater leaching to control soil salinization in lowland plains established. Through well-water irrigation, the critical level of shallow groundwater table was kept at >2-3 m during the dry season to reduce soil evaporation and control soil salinization. This was further reduced to 4-6 m before the rains to enhance rainwater recharge and in turn leaching of soil salts and dilution of saline groundwater. Next the groundwater table was kept at >0.5-1.0 m during the rains again to assure healthy crop growth. After the implementation of this method in Changzhuang Town (Nanpi County in Hebei Province) for the period 1983-1988, soil salt content decreased from 3.86 g·kg^-1 to 1.36 g·kg^-1, and the area of saline Chao soil and saline groundwater dropped by 76.2% and 42.8%, respectively. 2) The separation process of saline water and freshwater by melting saline ice and its infiltration into saline soil were revealed and the method of reclamation of coastal saline soils by freezing saline water in winter invented. Lab experiments showed that saline ice was desalinized efficiently by melting, which produced about 60% low salinity (< 4 g·L^-1) water from melting saline ice (< 15 g·L^-1). Also the infiltration of saline ice melt-water reduced surface soil salt content. Field experiments indicated that by freezing saline water (< 15 g·L^-1) irrigation in winter (< -5℃) combined with plastic film or straw mulching and rainwater leaching improved coastal saline soil. The soil salt content in 0-20 cm was less than 3.0 g·kg^-1 during the growing season under freezing saline water irrigation, while it exceeded 10 g·kg^-1 under control (no irrigation) treatment. 3) Trough coupling of the dynamics of soil salt and water, climate and plant growth, the agronomic patterns of soil salinization control in the root zone was established via ridging, mulching and straw incorporation into the deep soil layer. In monsoon climate regions, there was soil salinization in spring due to low rainfall and high evaporation, and then soil desalinized in summer due to high rainfall. Seed germination and seedling growth were the salt-sensitive stages, which usually occurred in spring. Therefore, it was important to create low salinity in the root zone for health growth of plant in spring. In order to desalinize the root zone soil, field ridging in spring and straw incorporation in autumn were studied. The results showed that field ridging, combined with plastic film and straw mulching, reduced soil salinity to 2.0 g·kg^-1 and straw incorporation into deep soil layer controlled the soil salinity in spring at < 3 g·kg^-1. 4) The adaptive mechanisms of halophytes to saline soils were explored and the pattern of efficient utilization of saline resources established. For the utilization of saline soils and saline water, salt tolerant plants and halophytes were collected and screened. The effects of salt stress, combined with those of water and nutrient application, on seed germination and plant growth were studied. The results showed that seed germination required low salinity, moderate salinity alleviated drought stress on seed germination and seedling growth, NO played a very important role in the regulation of salt tolerance of seedlings derived from dimorphic seeds of Centralasiatica atriplex, and N application increased the growth of halophytes under salt stress, etc. Based on the characteristics of salt tolerance of different plants, the method of growing plants in saline soils was established. This included land plowing, holing cultivation, fertilizer application, frozen saline water irrigation, mulching, etc. The application of the above results has supported crop production and ecological rehabilitation of saline soils in water-scarce regions of Bohai Sea.