A device used to measure the amount of water that percolates through a soil column, enabling direct measurement of evapotranspiration and deep drainage.
A lysimeter is a scientific instrument consisting of an isolated container of soil installed in the field to measure components of the water balance, particularly evapotranspiration (ET) and deep percolation (drainage below the root zone). Weighing lysimeters use precision load cells or scales to detect changes in mass of the contained soil-plant system, providing direct measurements of ET at high temporal resolution, often to an accuracy of 0.1 mm or better. Non-weighing (drainage) lysimeters collect and measure only the water that drains through the soil column, allowing estimation of deep percolation and leaching of solutes. Lysimeters are considered the gold standard for ET measurement and are used to calibrate other estimation methods such as the Penman-Monteith equation and remote sensing algorithms. They range in size from small laboratory columns to large field installations several meters in diameter and depth. While lysimeters provide highly accurate point measurements, their cost and maintenance requirements limit their widespread deployment. Data from lysimeter networks around the world provide critical reference datasets for agricultural water management, irrigation scheduling, and water balance studies.