Lysimeters

Lysimeters are devices used to measure the water balance of a defined soil-plant system under field or controlled conditions. They provide direct measurements of the amount of water entering and leaving a soil volume, enabling assessment of evapotranspiration, irrigation effects, and leaching losses.

A lysimeter typically consists of a soil column or monolith contained in a tank or chamber, sealed to prevent lateral water exchange with surrounding soil. Two common forms are weighing lysimeters, which measure changes in weight to infer evapotranspiration and drainage, and drainage lysimeters, which collect leachate for direct percolation measurements. Some systems continuously monitor weight or water content, while others rely on periodic sampling.

Water balance in a lysimeter is usually expressed as ET = P + I − D − ΔS, where P is precipitation, I is irrigation, D is drainage, and ΔS is the change in soil water storage. Data from lysimeters can be used to validate evapotranspiration models, calibrate remote sensing estimates, and optimize irrigation scheduling. They are employed in agricultural research, forestry, hydrology, and environmental studies to study crop water use and solute transport.

Limitations include scale and edge effects, soil disturbance during installation, maintenance costs, and representation of larger landscapes. While offering direct, site-specific measurements, lysimeters reflect the conditions of a bounded system and may not capture lateral flow or heterogeneity beyond the device.