The primary purpose of this study was to model the partitioning of
evapotranspiration in a maize-sunflower intercrop at various canopy covers. The
Shuttleworth-Wallace (SW) model was extended for intercropping systems to include both
crop transpiration and soil evaporation and allowing interaction between the two. To test the
accuracy of the extended SW model, two field experiments of maize-sunflower intercrop
were conducted in 1998 and 1999. Plant transpiration and soil evaporation were measured
using sap flow gauges and lysimeters, respectively. The mean prediction error (simulated
minus measured values) for transpiration was zero (which indicated no overall bias in
estimation error), and its accuracy was not affected by the plant growth stages, but simulated
transpiration during high measured transpiration rates tended to be slightly underestimated.
Overall, the predictions for daily soil evaporation were also accurate. Model estimation
errors were probably due to the simplified modelling of soil water content, stomatal
resistances and soil heat flux as well as due to the uncertainties in characterising the
2 micrometeorological conditions. The SW’s prediction of transpiration was most sensitive to
parameters most directly related to the canopy characteristics such as the partitioning of
captured solar radiation, canopy resistance, and bulk boundary layer resistance
