Theoretical analysis of the relationship between crop canopy - air temperature and vapor pressure deficit under temperate humid conditions
1991
Svendsen, H. | Jensen, H.E. | Jensen, S.E. | Mogensen, V.O. (Kgl. Veterinaer- og Landbohoejskole, Koebenhavn (Denmark). Dept. of Agricultural Sciences)
Based on the energy balance equation for a crop canopy a method is explicitly described for determination of a region of predicted values of crop canopy-air temperature in relation to vapor pressure deficit as well as for estimation of the lower base line as the best fit line through that region. Theoretical lower base lines are calculated for a number of climate crop parameter combinations (net radiation 500-700 W m-2, temperature 10-30 deg C, vapor pressure 0-3 kPa, aerodynamic resistance 5-25 s m-1 and crop resistance 20-60 s m-1) and the results are presented in terms of values of intercept and slope of the lower base lines obtained. Within the range of parameters employed the analysis showed that net radiation has only limited influence on the slope whereas the intercept increase for increasing values of net radiation, that slope and intercept increase and decrease, respectively, for increasing values of the aerodynamic resistance whereas the slope as well as the intercept increase for increasing values of the crop resistance. The ranges of intercept and slope were from 1.2 to 8.0 deg C and from -1.0 to -3.6 deg C kPa-1, respectively.
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