Mechanism of saline-alkali lands improvement of subsurface pipe drainage systems and agro-ecosystem response

Subsurface pipe drainage system is an efficient engineering approach to improve saline-alkali lands. It runs by controlling water tables to certain levels while leaching salt by rain-fed or irrigated water. Subsurface pipe drainage system changes the velocity, quantity and direction of soil water and salt movement. This induces soil salt redistribution and variations in soil features. This paper firstly summarized the technological development of subsurface pipe drainage system, discussed the conditions (natural and ecological) of application and the key engineering parameters. Based on literature analysis, the mechanism and response of agro-ecosystems to subsurface pipe drainage system regarding improving saline-alkali lands were then presented. Numerous research on the mechanism of subsurface pipe drainage systems had mainly focused on: 1) changes in circulation principles of precipitation, surface water, soil water and groundwater, especially the relationship between agriculture and water table level, irrigation system, waterlogging. 2) The features of soil water and salt migration under controlled and fixed water table drainage. Under controlled drainage conditions, soil salt varied with drainage frequency and intensity at supportable soil water content. Under fixed water table drainage conditions, the depth of subsurface pipe and the spacing between side-by-side pipes regulated drainage water and salt movements. 3) Simulated and modeled soil water and salt migration features. These researches focused on the theoretical innovation, key parameters determination, validation and suitability. Also research on agro-ecosystem response had mainly focused on: 1) soil features in ago-ecosystems; 2) adaptable crop planting, including physiological and ecological responses of crop growth, quality and yield to subsurface pipe drainage system; and on 3) agro-ecosystem structure and functional responses, including tillage system, land use and ecosystem services promotion. Finally, this paper put forward two strategies of future research on subsurface pipe drainage systems and applications.