Abstract
In order to measure the actual value of potential-evapotranspiration (PE) (tankPE+rain-drained water) of upland rice and barley in field with volcanic ashy loamy soil, we used the tank, diameter 4m, depth 50cm, ground water level 45cm from field surface, like that by Thornthwaite.
The tank was surrounded by the same crops raised by ordinary method, where ground water level is below morethan 15m.
The amount of water evapotranspirated from the tank and also from a standard pan used in Japan, its diameter 20cm, hight 10cm, were measured, and we obtaind the following results.
a) The evapotranspiration by Blaney and Criddles, Thopnthwaite's methods were of less accuracy compareing to that from the pan.
b) PE was found to be a function only of meteorological factors, regardless of the growth stages of crops.
c) PE was about 1.2 times the amount from the pan in each month of the growing season.
d) The actual PE is calculated with considerable accuracy by actutl PE=tank PE in no- rain
period×mean daily amount of pan evaporation in each month/mean daily amount of pan evaporation in no-rain period of the corresponding month
