VALIDATION OF GOUDRIAAN MODEL - A CASE-STUDY FOR MAIZE

The crop micro-weather model of Goudriaan was tested, using data collected in a maize field during one day. The simulated results are described and validated with actual field measurements, which were carried out, over the maize crop canopy, during the middle of the summer of 1986. Except for the soil heat flux, latent and sensible heat fluxes are simulated reasonably well. The model of Goudriaan overestimates the latent and sensible heat fluxes above the crop canopy by 9 and 10%, respectively, in comparison to the latent and sensible heat fluxes measured with the eddy correlation technique. The simulated fluxes can still be improved upon by a better incorporation of the effect of dewfall in the model. The canopy and soil temperatures were also estimated and described in relation to the observed data from the field. Root mean square error of the simulated soil temperatures at 1, 5, 10 and 20 cm depth were found between 0.30 K and 0.68 K. Further, sensitivity analysis of the model showed that the heat fluxes are more sensitive to soil than to crop parameters, for the same magnitude of variations. Among soil parameters, the soil surface resistance to evaporation has large influence on the latent heat and the sensible heat fluxes at soil surface; in addition it also has influence on the soil heat flux. The soil water stress has high influence on the daily net CO2 assimilation as well as the latent and the sensible heat fluxes above the crop canopy.