A SIMPLE-MODEL FOR SIMULATION OF GROWTH AND DEVELOPMENT IN FABA BEANS(VICIA-FABA L) .2. MODEL EVALUATION AND APPLICATION FOR THE ASSESSMENT OF SOWING DATE EFFECTS

An evaluation of a faba bean model was undertaken to obtain indication s whether the description of the physiological relationships in the mo del and the assumptions made realistically described the effects of va riation in sowing date. Comparisons of simulated with experimental dat a for indeterminate and determinate cultivars of Vicia faba revealed t hat the model made good predictions of leaf area index, total and frui t dry matter until early June. Thereafter, the model consistently over estimated dry matter production. This was presumed to be due to aphid and virus infestation for which no provisions were made in the model. Linear reductions of light use efficiency from the third decade of Jun e on resulted in satisfactory model results for the indeterminate cult ivar. In the determinate cultivar, the pest apparently accelerated lea f senescence which had also to be taken account of in the model. Simul ations of systematic variations of sowing date revealed that the obser ved yield reductions due to delayed sowing were probably due to pests when a constant thermal duration of the reproductive phase was assumed . When the thermal duration of the reproductive phase was decreased wi th later sowing dates, yields decreased even without pests.