Preliminary Study of the WRSIS Concept at the Paddy-Upland Crops Rotation Area in Southern China

Abstract

The central demonstration zone of the 16.47 acre Wetland Reservoir Sub-irrigation System (WRSIS) concept field is summarized based on current conditions including irrigation and drainage systems with subsurface drain pipe, constructed wetland, water supply reservoir, monitoring system and other related facilities. The irrigation water is imported from the reservoir to the underground pipeline network by pumping. The drainage waters are routed to the constructed wetland system under gravity through the drainage pipe network. The constructed wetland system consists of three components for drainage water treatment; a ditch wetland, a subsurface vertical flow component, and a surface flow component. Treated water is then routed to the reservoir by pumping. The purpose of the study is to study the effect of the WRSIS concept in increasing crop yields and improving water quality, to study how to link the constructed wetland and irrigation/drainage systems, to identify the best type and size of a constructed wetland and identify the optimum local wetland vegetation, and to reduce the agricultural non-point source pollution by using water-saving irrigation technology and controlled drainage technology. These goals are under study as potential modifications of the WRSIS concept as applied to China. A two-year preliminary study showed that the hydraulic structure used to control the outlet water level is appropriate to control water table in paddy field, and helps increase the use of irrigation water and rainfall. The structure has proven useful to drain rice and upland crops and increase the yields. A reduction in total nitrogen (TN), total phosphorus (TP), NH3-N and NO3-N through components of the constructed wetland treatment system is being observed compared to the controls in preliminary studies. The application of the WRSIS concept on the aquatic environment restoration in paddy and upland crops rotation areas in China is being researched further.