Hydraulic Load‐Cell Lysimeter, Construction, Calibration, and Tests

Abstract

The construction and calibration of two 35‐metric ton, hydraulic load‐cell lysimeters with suction drainage systems are described. The butyl‐nylon load cells contain an ethylene glycol‐water mixture and pressures are measured with a capacitive pressure transducer. Lysimeter sensitivity is 0.02 mm evaporation. Daily evaporation from the lysimeter and the two independent micrometeorological methods agreed to within 5%. On a June day, lysimeter measurements of evaporation from bare soil lagged measurements using the two other methods by almost 1.5 hours. Differences between the lysimeter thermal regime and that in the surrounding soil accounted for the lag. By using foam plastic insulation of the tank walls, thermal regime differences were minimized.