A crop of chrysanthemums was grown on a lysimeter in a variable shade
greenhouse. Measurements were made of evapotranspiration (ET), air vel
ocity, air temperature, air dew point temperature, carbon dioxide conc
entration, leaf temperature, leaf area, and photosynthetically active
and global solar radiation. Comparisons were made between the evapotra
nspiration of the crop and the predicted water use from a computer mod
el that used temperature, relative humidity, and solar irradiance leve
ls as inputs (the combination model). The ET was studied as a function
of vapor pressure deficit (VPD) and solar irradiance levels both sepa
rately and together. A relationship between stomatal resistance and so
lar irradiance levels for chrysanthemums was established.