A "pan coefficient
" [k.sub.p], typically -0.70, is multiplied by the change in water depth to account for the overestimation of E.
The present study adopted a mean Class A pan coefficient
of 0.75, in agreement with studies conducted in a nearby experimental area alluvial, also in the municipality of Pesqueira, by Santiago et al.
The Kp is the pan coefficient
and E pan is the Class A pan evaporation (mm).
Importance of pan evaporation for irrigation scheduling and proper use of crop-pan coefficient (Kcp) crop coefficient (Kc) and pan coefficient
In order to determine reference operation E[T.sub.o], one has to multiply the data from the evaporation pan with pan coefficient
that can be chosen from 1 to 2.1, with the interval of 0.1 .
where: CWR is crop water requirement (mm [d.sup.-1]), [K.sub.c] is the crop coefficient, [K.sub.p] is the pan coefficient, [E.sub.pan] is pan evaporation (mm) and P is precipitation (mm).
In Puerto Rico, the pan coefficient values commonly used were derived from a study by Gonzalez and Goyal (1989).
(#) Seasonal reference evapotranspiration ([ET.sub.r]) = pan coefficient x pan evaporation.
([sections]) [ET.sub.r] = Seasonal reference evapotranspiration = pan coefficient x pan evapotranspiration.
No plants were grown, and potential evaporation was taken as the measured pan evaporation with a pan coefficient (mm of potential evaporation per mm of evaporation from the pan) of 1.0 mm/mm.
Evapotranspiration is often not directly measured in field experiments and it is necessary to obtain the pan coefficient as well as the mineralisation rate parameter from the data.
The pan must be properly constructed, located and managed for accurate use in irrigation scheduling, and a suitable pan coefficient
must be determined as well (Huang et al., 2002).