An atmometer device comprises a porous evaporator member, a suctiontube communicating water from a reservoir to the porous evaporator member, asensor measuring a moisture characteristic of soil associated with a crop, amechanism arranged for controllably varying a rate of evaporation of the waterthrough the porous evaporator member responsive to the moisture characteristicmeasured by the sensor, and an indicator arranged to indicate water loss inthereservoir. By controlling rate of evaporation of the water through the porousevaporator member responsive to the measured moisture characteristic of thesoil,the amount of water loss in the reservoir during the given time period moreaccuratelyreflects crop evapotranspiration.
