1)Introduction of Yucheng GAS

Groundwater-Agroecosystem Experimental Simulator at Yucheng Station

       The Yucheng GAS integrates nine subsystems, including a large sealed-bottom sample plot subsystem, an automatic groundwater level control subsystem, a soil temperature-moisture-salt monitoring subsystem, a soil water collection subsystem, a root growth monitoring subsystem, a groundwater quantity and quality dynamic monitoring subsystem, a critical zone dynamic monitoring subsystem, an agricultural ecosystem water-carbon-nitrogen interaction subsystem, and a near-surface unmanned crop growth-multispectral monitoring subsystem. Through the integrated monitoring system consisting of multi-method positioning monitoring, multi-element stratified analysis and multi-scale three-dimensional monitoring, Yucheng GAS can support basic experimental research and international frontier exploration related to carbon, nitrogen, water and nutrient cycle of farmland ecosystem, food security, ecological security and environmental security under the scenario of groundwater dynamic change.

       For the future of Yucheng GAS, it’s expected to attract more researchers to conduct collaborative research, and establish mechanisms for opening, use and share the platform to the outside world, regulations related to the opening and sharing of the platform, data sharing regulations and attribution of results are formulated for this purpose. The academic committee will be the core to guide the medium and long-term scientific development planning and data sharing of the platform. The research facility will be open for sharing by domestic and foreign experts in agronomy, ecology, geography, meteorology, hydrology, environmental science and other related research fields.

2) Mission and Objectives of the Yucheng GAS

       Ycheng GAS aims to promote crossover and innovation in the fields of agronomy, ecology, geography, climate change, and hydrology and water environment, and to promote the development of the discipline; to train and attract talents to conduct cutting-edge and outreach research; to comprehensively enhance the comprehensive research capability of Yucheng Station, and to play a role in China's agricultural ecosystem research and innovation.

3) Scientific background

       The lower reaches of Yellow River irrigation area is one of the important food security guarantee bases in China. Since the great development in the HuangHuaiHai Plain, experts from the Chinese Academy of Sciences and other organizations have made strenuous efforts here to achieve abundant and stable grain production in the area. Currently, the three provinces of North China (Hebei, Henan and Shandong), which are mainly in the plains, account for 23.8% of the national production of grain. However, grain production comes at the cost of consuming large amounts of water resources and has led to water shortages with socioeconomic development, thus causing a decline in groundwater. Combined with the effects of climate change, the lack of water resources for agriculture in China is particularly serious. In addition, the ecological and environmental problems brought about by agriculture, especially the excess of nitrogen and phosphorus and greenhouse gas emissions, have also received continuous attention in recent years. According to the monitoring results of Yucheng station in the past 20 years, the overall trend of groundwater depth in the lower reaches of Yellow River irrigation area is gradually increasing, especially in the past 10 years, the continuous decline is very obvious. It is especially serious during the re-greening and tasseling periods of winter wheat and when the lack of water supply from the Yellow River is superimposed - the depth of groundwater can be reduced to less than 7 m for a short period of time. In addition, the decrease of incoming runoff from the Yellow River is also one of the important reasons for the decrease of groundwater depth in the lower reaches of the Yellow River.

       Groundwater decline has become an unavoidable problem in the lower reaches of Yellow River irrigation area, how will the soil structure change as a result? What will be the response of crop growth? How will agricultural ecosystem processes be affected? What are the possible ecological and environmental effects? Yucheng GAS will conduct future-oriented scenario studies to address the above-mentioned series of related scientific questions.

4) Structure and Function of Yucheng GAS

       The Yucheng GAS covers an area of 1400 m2 and a total of 3 underground floors. It consists of the following 9 subsystems.

       (1) Large-scale sealed-bottom plots. The Yucheng GAS consisted of 16 large sealed bottom plots, 10 m long, 5 m wide and 8 m high, with a sample area of 50 m2, which is the recommended sample area for agroecosystem trials by the Food and Agriculture Organization of the United Nations (FAO), to ensure that the samples were not duplicated within a sufficient period of time.

       (2) Subsystem for groundwater level automatic regulation and control. This subsystem has 2 modes of manual control and automatic control; among them, the manual control can be used for valve opening and closing and water level collection test. The subsystem can regulate the groundwater level of each sample site individually. The water level control range is 0-8 m, and the control accuracy is 2 cm. 16 stainless steel water columns with level observation tubes are set as the control columns, and each sample site is connected to one control column through the pipeline and related water flow control equipment; the control method is to obtain the real-time level of the water column through the collector. According to the upper and lower level settings provided by the software interface, the water inlet valve and drain valve are controlled to open and close to maintain the water level between the upper and lower limits. The software interface can set and adjust the hardware equipment connection relationship, can display the current water level value in real time, and save data records.

       (3) Subsystem for soil temperature-moisture-salinity monitoring. The subsystem consists of a sensor (Campbell Scientific, model CS655), a data collector (Campbell Scientific, model CR6), and a wireless transmission system. The system was designed to measure temperature, moisture (water content), and salinity (EC) at 10, 20, 40, 60, 100, 200, 300, 400, 550, and 750 cm soil depths, respectively. The data will be used to support the study of water table fluctuation and rainfall, and the response to crop evapotranspiration.

       (4) Subsystem for soil water collection. The system is composed of clay head, vacuum pump and sampling bottle. A domestic split type soil solution collector was used. The clay head is protected by a 25 mm Plexiglas connector and fitted with 2.2 mm and 3.2 mm diameter stainless steel tubes respectively; among them, the 2.2 mm diameter tube extends straight to the bottom of the clay tube and the other extends to the upper end of the clay tube and connects to two polyethylene hoses, and the soil solution collector hose is left 70-100 cm in the ground and protected by a plastic sleeve. Clay head buried depth of 40, 60, 80, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750 cm each buried 1, horizontal depth of 2.0 m in the soil; sample plot around the edge of the wall of the moisture movement on its impact as small as possible to ensure the scientific nature of the acquired data. The horizontal distance from the water temperature and salt sensor is about 20 cm, and the water around the soil is transferred into the sampling bottle by negative pressure. Soil water samples can be analyzed for stable isotopes, elements, conventional nutrients, heavy metals and organic pollutants to provide data support for material transport in farmland ecosystems.

       (5) Subsystem for root growth monitoring. Two root windows of 750 cm in length and 20 cm in width were installed in each plot to observe the root growth dynamics. At the same time, three 4.5 cm diameter and 2 m long root tubes were installed in each plot to measure the crop root growth process regularly by root scanner. For special growth periods, the roots were sampled by manual root auger, and the root system was washed for quantitative study by root scanner.

       (6) Subsystem for groundwater water quantity - water quality dynamic monitoring. automatic monitoring sensors for groundwater level, temperature and salinity have been installed in each plot to obtain dynamic changes in groundwater quantity and quality (collected once every 30 min) to support the joint water quantity-quality response study. Collection of groundwater samples for water quality analysis can help reveal the interaction between groundwater-soil-crop-atmosphere continuum in agricultural ecosystems.

       (7) Subsystem for critical zone dynamic monitoring. Regular scanning of sample plots with electrical resistivity tomography (ERT, Chongqing Geological Instrument Factory, China, model DZD-8), combined with in situ soil water temperature and salt monitoring results, can resolve the spatial distribution mechanism of long-term tillage and groundwater level fluctuations on physical structure and physicochemical properties of soil such as salinity.

       (8) Subsystem for water-carbon and nitrogen interactions in agricultural ecosystems. The system will combine an assimilation chamber (Picarro Model 2508, USA) and a greenhouse gas analyzer (Thermo Fisher Model 17i, USA) to conduct cross-sectional studies on crop photosynthesis, respiration and soil greenhouse gases (including CO2, CH4 and N2O), as well as ammonia (NH3), nitrogen oxide (NO and NO2) emissions, crop productivity, and carbon, nitrogen and phosphorus cycling.

       (9) Subsystem for near-ground UAV crop growth-multispectral monitoring. The UAV (DJI, China, model M600 PRO) with a small airborne multispectral instrument (PEAU, USA, model S3) and a high performance airborne thermal infrared imager (Workswell, Czech Republic, model Pro) were used to scan 16 plots periodically to obtain the heat distribution and crop spectral distribution under different treatment conditions; then, combined with the ground biometric data and micro-meteorological data, we can analyze the crop growth, assess the crop nutrient status, and predict the crop yield. Therefore, the crop growth, nutrient status and yield prediction can be analyzed by combining the ground biological measurements and micro-meteorological data.

Structure and function of Yucheng GAS

       To accommodate the shared needs of the platform, the number of plots, the adjustable range of groundwater levels (0-8 m) and the functions of the Yucheng GAS have been extended compared to the previous experimental devices. In particular, the functional extension of the Yucheng GAS has improved the research content compared to the hydrology and water monitoring devices in the other water resources departments. In addition, the existing sensors are buried in the ground, so that scientists from different disciplines can bury new sensors according to their needs, and there is enough space to carry out scientific research above the ground.