An Automated Suction Lysimeter for Improved Soil Water Sampling

Leaching of chemicals (e.g., fertilizers, manure, pesticides, and petroleum products) from urban regions and areas impacted by human development is one of the main sources of underground nonpoint-source pollution. Most methods of soil water sampling are not capable of extracting representative soil water samples to determine leaching volume and solute concentrations since they fail to create normal leaching conditions in the soil. Thus the volume of soil-water collected, as well as its solute concentration, may not be accurately estimated. Sixteen units of cost effective and accurate automated lysimeters were designed and installed to measure post-harvest nitrate leaching from a rye (Secale cereale L.) cover crop field during the falls and winters of 2007 to 2009. Major parts of the electronic system were electronic controller, data logger memory, digital clock and its battery backup circuit, relays, LCD display and electronic signal conditioning interfaces for amplifying, off-setting, and digitizing the signals from vacuum sensors. The electronic system was designed to monitor soil tension every second with accuracy of 1 cm and apply the proper amount of suction to the sampling media (ceramic plate). Hourly data from soil tension and vacuum applied to the system were collected and stored by each unit. A safety system was designed for protecting the vacuum pump against unexpected major vacuum leakage events. The controller can be easily reprogrammed for different performance strategies. The automated lysimeter showed an accurate and reliable performance in both lab and field conditions. Ambient soil matric pressure and matric pressure above the samplers indicated a strong linear correlation which confirms that the lysimeter was successful in maintaining the sampler vacuum in equilibrium with soil.