Abstract
Six different modules for dry matter production of cauliflower were parameterised and evaluated using a database of 22 cauliflower crops originating from 15 independent field experiments. The evaluation included a light use efficiency, LUE, based module assuming LUE to be constant, an LUE based module assuming a linear decrease of LUE with increasing daily photosynthetically active radiation sum, I, two photosynthesis–respiration based modules using an analytical integration of the rectangular hyperbola over the canopy, assuming either the light saturated photosynthesis rate of single leaves, P max, to be constant or to decrease proportionally to irradiance within the canopy. Furthermore two slightly modified versions of the light interception and photosynthesis algorithms of the SUCROS model were evaluated, where the negative exponential equation for single leaf photosynthesis was replaced by the rectangular hyperbola. In order to make these modules comparable with the analytical integration approach, P max was also assumed to be either constant or to decrease proportionally to irradiance within the canopy. The results indicate that an estimated constant LUE (3.15 (±0.04) g MJ −1) is only poorly able to predict total dry matter production for cauliflower (modelling efficiency EF=0.69) of an independent data set. Using a linear decline of LUE with I (LUE=6.66 (±0.80)–0.36 (±0.08) I) drastically increased the predictive value (EF=0.88) of the LUE approach. The descriptive and predictive value of the photosynthesis based modules was higher when assuming that P max declines within the canopy. Then the predictive value of the photosynthesis/respiration based approach was better than the simple LUE approach but not generally better than the LUE approach assuming a linear decrease of LUE with increasing daily radiation sum.
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