Water Management in Horticultural Crops

2.Radiation method

The crop evapotranspiration is estimated by the formula

Where,

C=the adjustment factor made graphically on W.Rs using estimated values of RH mean and day time wind velocity
W= the temperature and altitude dependent weightage factor
Rs=the solar radiation in equivalent evaporation (mm/day)
Rs can be measured directly by solar monitor with pyranometer sensor. It can also be obtained from measured sunshine duration records as
Rs=(0.25+0.50 n/N)RA

Where,

RA= the extra terrestrial radiation in equivalent evaporation in mm/day
n = actual measured bright sunshine hours
N= maximum possible sunshine hours