Construction technology and application of lysimeter in agricultural soil environment monitoring

In recent years, intensive and extensive farm managements have resulted in a decline in the quality of cultivated land. Excessive inputs have been leached from farmland to rivers and lakes, especially the leaching of nutrients, heavy metals and pesticide residues, which has aggravated the risk of pollution to agricultural environment. As a critical methodology of agricultural environment monitoring, the lysimeter has been applied to monitor the characteristics of soil leaching components, to simulate the migration of soil water and nutrients, and to assess the effects of farm managements on agricultural ecosystems, eventually to provide technical assistance for scientists to make a better management decision in the farmland ecosystem. In this paper, the methods of construction, layout, soil filling, soil surface isolation and sampling in the main types of lysimeters monitoring system were summarized. Based on that, the merits and shortcomings of different types of lysimeters were analyzed, and the main factors affecting the monitoring results of lysimeter were discussed. In the end, suggestions and prospects were put forward based on the current situation of lysimeter in agricultural environment monitoring. Overall, for the rectangular concrete lysimeter, the biggest advantage is that cost of construction and operation and requirements for technology is relatively low, however, large quantities of soil excavation, concrete construction and soil back filling are always time-consuming and usually cause high soil disturbance and significant artificial effect and need to undergo a transition period. Besides that, the problem of infiltration from inside to outside at the bottom and side of concrete lysimeter also needs to be overcome. Conversely, for barrel or vessel lysimeter, the monolith soil usually undergoes minimal disturbance by extracting and filling the cylindrical blocks, the process is much more simple, which can be achieved just by mechanical equipment including cutting system, crane, trucks and so on. It takes shorter time compared to concrete lysimeter, the whole procedure of obtaining monolith soil just takes one day or more and can be put into use immediately without transition period. Consequently the soil conditions are more comparable to natural field conditions and data could be accurately detected and collected. However, the technological and equipment requirements of monolith soil extraction, filling and transportation are relative high, as well as the cost of construction and operation. Besides that, boundary effect is much more significant compared to the concrete lysimeter due to the minimal soil base area. The artificial effect and boundary effect cannot be eliminated completely at the same time in the semi-closed lysimeter system, the selection and construction of lysimeter system should be depended on specific research needs, local geological and topographic conditions and their own technology level. Therefore, a more practical strategy need to be taken into consideration, that is to build a more suitable lysimeter within the acceptable deviation range and the given budget, being able to implement higher data accuracy with lower costs. Finally, building and running a long-term lysimeter station with continuously improved technologies, joining a platform, sharing methods, data and models, and constructing a network of lysimeter system are also recommended.