A MODEL TO SIMULATE THE DEVELOPMENT, GROWTH AND YIELD OF IRRIGATED SUNFLOWER

A simulation model of the development, growth and yield of sunflower cv. Hysun 30 is presented. In the model, crop growth rate is a function of radiation use efficiency, incident radiation, the canopy extinction coefficient and leaf area index. The radiation use efficiency of a sunflower canopy was measured and found to change during the growth of the crop. It is higher after floret initiation than before, and reaches a maximum at anthesis. The changing radiation use efficiency has been incorporated into the model. The leaf area index each day is a function of the number of leaves produced and the rate and duration of expansion of each leaf. A nitrogen and plant population factor modulates crop growth through its effect on the expansion rate of each leaf and the rate of leaf senescence after anthesis. In this way the nitrogen concentration in leaves at floret initiation and population density affect the dry-matter accumulation by the crop. Crop dry matter at the end of floret initiation and at physiological maturity are used to calculate the components of yield from relationships previously demonstrated in greenhouse experiments. The mean daily temperature affects the rate of leaf production and the radiation use efficiency, as well as determining the time of phenological stages through thermal time. Although the model was developed for the hybrid Hysun 30, it has been extended to some other hybrids by changing the size and activity of the generative area producing florets in the floral meristem. The simulated yields of four hybrids are close to the measured yields of irrigated crops.