SVERIGES LANTBRUKSUNIVERSITET - Epsilon Open Archive - SLU

92
Brief deseription of the eomputer programs developed is
given exeluding all mathematieal equations. The main em­
phasis is devoted to the input variables needed in the models
and to the output variables eomputed by the simulation
programs.
Program 1: CropWP - eomputation of erop water balanee and
eanopy photosynthesis on a seasonal basis
The purpose of this program is to eompute the water
balanee of the eropincluding estimation of transpiration and
crop photosynthesis over the whole growing season. The
effect of soil water content on transpiration and erop photo­
synthesis is taken into aceount. This program can be used to
predict the need for irrigation when soil type and the meteo­
rological driving variables are known. Soil parameters can
be taken based on so il texture as described by Driessen
(1986) or pF-curve and hydraulic conduetivity funetion can
be measured directly.
The meteorological input variables needed are:
· solar radiation
· air temperature
• precipitation
• relative humidity or vapour pressure deficit (VPD)
· wind speed
The most important parameters needed are:
• crop biomass allocation over various plant organs
• crop light response curve (photosynthetically active
radiation versus leaf photosynthesis)
• soil pF-curve and hydraulic conductivity
The program CropWP is capable of eomputing potential and
actual transpiration and photosynthesis rates on a daily
basis. Moreover, the soil water content profile can be
computed.
The computation of crop water balance is largely based
on ideas presented by Federer (1979) and Choudhury and Idso
(1985a and 1985b). The computation of canopy photosynthesis
resembles very closely the methods presented by Spitters
(1986) and Spitters et al. (1986). The models for computa­
tion of soil water balance have been described by Karvonen
(1988). Unfortunately there exist so far no complete data