Abstract:The Luancheng Agro-Ecosystem Experimental Station, the Chinese Academy of Sciences, is located in the piedmont plain area of North China Plain and the middle section of the Taihang Mountain alluvial plain. It is a typical representative of the high-yield agricultural eco-system in the groundwater irrigation area. Due to the large-scale and high-intensity agricultural production in recent decades, the regional groundwater has been seriously over exploited, and the risk of groundwater pollution has increased. However, the surface agro-ecosystem and aquifer are separated by thick vadose zones, hence the mechanism of the impact of surface agricultural activities on the quantity and quality of groundwater is still unclear. The in-situ monitoring throughout the entire vadose zone is the only method to reveal the mechanism of this process. Therefore, the establishment of a large-scale critical zone observatory is the most important requisite for conducting research on the relationship between agriculture and groundwater. With the support of the cornerstone research infrastructure project for the field station network of the Chinese Academy of Sciences, Luancheng Station began to construct the “Water and Solute Cycle Observation Platform in Groundwater-Soil-Crop System” in 2016, and the construction was completed in November 2020. An observatory caisson with a depth of 48 m and an inner diameter of 2.8 m has been built. The platform was officially named ‘Luancheng Critical Zone Observatory' (LC-CZO). LC-CZO can measure the key variables such as soil water content, matric potential, soil temperature, and solute concentration in the root zone-deep vadose zone-saturated zone. The monitoring results enable the study on the patterns of the transport and transformation of water, solutes and pollutants in the thick vadose zone reveal the hydrological process of the saturated-unsaturated transition zone and its relationship with groundwater replenishment, explain the migration and transformation of nitrogen applied in farmland and its impact on groundwater quality, and provide experimental platform support for exploring the impact mechanism of land surface process on the groundwater quantity and quality.