OILCROP-SUN - A DEVELOPMENT, GROWTH, AND YIELD MODEL OF THE SUNFLOWERCROP

Crop simulation models are important tools for agronomic management st rategy evaluation, particularly under rainfed conditions. This paper d escribes the structure and testing of OILCROP-SUN, a process-oriented model of the sunflower (Helianthus annuus L.) crop. The model simulate s organ biomass and N content, leaf area index, and soil water and N b alances with a daily time step. Daily weather data, soil physical and chemical characteristics, and initial contents of water and N are requ ired inputs. Three cultivar-specific parameters synthesize crop respon ses to temperature and photoperiod during development, and two cultiva r-specific parameters define potential grain number per capitulum and potential kernel growth rate, Tested against independent data sets, th e model generated good predictions of the durations of the sowing-emer gence (range 7 to 32 d; root mean square error [RMSE], observed vs. si mulated: 3.7 d) and emergence-anthesis phases (range 52 to 146 d; RMSE between 2.9 and 4.3 d, depending on the cultivar). The model also sim ulated seasonal crop biomass and leaf area dynamics for irrigated and rainfed crops sown at two densities satisfactorily, as well as aerial biomass (range 5 to 15 t ha(-1); RMSE 1.7 t ha(-1)) and grain yield at maturity (range 1.0 to 6.2 t ha(-1); RMSE 0.8 t ha(-1)) for irrigated and rainfed crops sown at a range of population densities (0.5 to 10 plants m(-2)). We conclude that OILCROP-SUN can be used to simulate bi omass and grain yields over a wide range of conditions.