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