Water Management in Horticultural Crops

4.3.Piche atmometer

• Piche atmometer is sometimes used to measure the evaporation rate. It consists of a graduated tube 1.5 cm in diameter and 30 cm long with one end open and a flat horizontal disc of drier paper placed to the open end. The tube is filled with water and then the drier paper placed in position and held to the tube by a metallic device. Atmometer is laid in an inverted position for evaporation measurement in the field. Water from the tube wets the paper slowly and evaporates from the paper. The loss of water is read on the graduated tube that gives the measure of evaporation.
• The rate of evaporation from atmometer is usually higher than that obtained from USWB Class-A pan evaporimeter and is poorly correlated with the crop ET. It tends to overestimate the wind effect and grossly underestimate the radiation effect. The evaporating surface of the unit is often subjected to contamination by dust, oil and other foreign materials interfering with the evaporation process.