Water-salt control and response of Chinese rose (Rosa chinensis) root on coastal saline soil using drip irrigation with brackish water

Coastal saline land is an important resource in coastal area, with the development of urbanization process and ecological civilization construction, there is an urgent need to improve the landscape to meet the demand of living environments for cities and districts. Presently the main method of vegetation rehabilitation is to replace saline soil with non-saline soil for depths of 0-100 cm. However, this method is expensive and unsustainable due to the shallow and saline groundwater, thus a technology of low cost, rapid and sustainable for re-vegetation on coastal saline land is needed. A common practice for reclaiming salt-affected soils is leaching of soils to move excess soluble salts from upper to lower soil depths or out of the root zone, while large scale of salt leaching will consume large quantities of water, and supplies of fresh water are already low in coastal regions, thus likely saline water rich in coastal regions are alternatives to freshwater resources. For the landscape construction in coastal saline land and saline/ brackish water utilization, a field experiment was conducted on the sandy saline soil formed by sea reclamation at Caofeidian District near the Bohai Gulf in 2012-2014. Five treatments of salinity levels of 0.8, 3.1, 4.7, 6.3 and 7.8dS/m of irrigation water was imposed. A gravel-sand layer was created at 100 cm depth. Tensiometers were buried at a depth of 20 cm to control the soil matric potential (SMP), keeping the SMP over - 5 kPa at first year, and over -10 kPa at second year, and over -15 kPa at third year. Chinese rose (Rosa chinensis) was chosen as the representative plant. Salt leaching characters and root growth and distribution were studied. The results showed that: under the climatic condition in the coastal area of Bohai Gulf, when fresh water was applied using drip irrigation for salt enhanced leaching and seedling establishment first in a short period, and then followed drip irrigation with water salinity <7.8 dS/m, soil salinity decreased significantly in 0-100 cm soil profile, especially in 0-40 cm soil profile, soil salinity decreased from 28.33 dS/m to <4 dS/m taking one month. Irrigation water depth for soil salinity decreased from 28.33 dS/m to 4 dS/m in 0-40 cm soil profile for <7.8 dS/m irrigation water salinity were 160-220 mm, and 8-20 mm of water depth is needed for soil salinity of 1 dS/m decreasing. The soil desalting process can be described by the logistic equation, and it can be divided into three stages including rapid desalting, slow desalting and salinity stabilization. More than 94% of the roots are mainly distributed in the topsoil of 0-20 cm. The root biomass decreased significantly with irrigation water salinity increasing, and the root is affected by the physiological drought of salinity stress to expand the water space in the deep soil. More winter irrigation water depth needed when there is less rainfall after October to prevent salt accumulation in topsoil in the spring of next year. The method of drip irrigation with fresh water for salt enhanced and seedling establishment in a short-term and subsequent drip irrigation with saline/ brackish water can be used to realize the rapid salt leaching and maintain lower soil salinity, but the appropriate irrigation water salinity threshold should be determined in combination with salt tolerance of plant and the production target as root growth suffered salt stress and thus affect the growth of plant and its survival. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.