A model to predict growth and yield of sunflower

We have developed further a preliminary model (2) which simulates the growth, development and yield of sunflower cv. Hysun 30. The inputs needed are maximum and minimum daily temperatures, daily irradiance, plant population density, and date and latitude of sowing. The developmental phases of the crop (emergence, completion of floret initiation, first anthesis and physiological maturity) are calculated from daylength and temperature (1,6). Estimates of the areas of individual leaves are generated (5). These are modified by leaf N concentration at floret initiation and population density (affecting the rate of leaf expansion) and leaf position (affecting the duration and rate of leaf expansion). Leaf area per plant is also modified by temperature (affecting leaf number). The progress of leaf senescence in sunflower needs more investigation but in the model it starts at full anthesis with the rate being constant over time and scaled according to leaf N status and population density. The accumulation of shoot dry matter is derived as a function of incident radiation, canopy light interception and the efficiency of conversion of energy to dry matter. The latter is temperature dependent (7)..