Predicting dry matter production of cauliflower (Brassica oleracea L. botrytis) under unstressed conditions - Part II. Comparison of light use efficiency and photosynthesis-respiration based modules

Six different modules for dry matter production of cauliflower were paramet erised and evaluated using a database of 22 cauliflower crops originating f rom 15 independent field experiments. The evaluation included a light use e fficiency, LUE, based module assuming LUE to be constant, an LUE based modu le assuming a linear decrease of LUE with increasing daily photosynthetical ly active radiation sum, I, two photosynthesis-respiration based modules us ing 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 th e canopy. Furthermore two slightly modified versions of the light intercept ion and photosynthesis algorithms of the SUCROS model were evaluated, where the negative exponential equation for single leaf photosynthesis was repla ced by the rectangular hyperbola. In order to make these modules comparable with the analytical integration approach, P-max was also assumed to be eit her 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 cauliflowe r (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 incr eased the predictive value (EF=0.88) of the LUE approach. The descriptive a nd predictive value of the photosynthesis based modules was higher when ass uming that P-max declines within the canopy. Then the predictive value of t he 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. (C) 2001 Elsevier Scie nce B.V. All rights reserved.