Date of this Version
Mechanistic crop simulation models can aid in integrating and directing research, and in improving farm management strategies. Information derived from recent research on spike development and growth of winter wheat (Triticum aestivum L.) was incorporated into a submodel, SPIKEGRO, and added to an existing model called SHOOTGRO. This manuscript discusses the SPIKEGRO submodel. SPIKEGRO emphasizes the reproductive functioning of the shoot apex. The complete developmental sequence of the shoot apex is outlined and quantified. All developmental events and growth stages are predicted, most using the phyllochron approach. Spikelet and floret primordium initiation, growth, and abortion; ovule fertilization and growth; and rachis and chaff growth are simulated on morphologicallyidentified culms. The phyllochron interval, rather than growing degree-days, is used throughout the model to increase flexibility in predicting yearly and within-stand variation in development. Up to six cohorts of plants are simulated simultaneously from time of emergence, using a daily time step. Initial inputs consist of general agronomic information such as planting date, density, and depth, site latitude, cultivar heightclass, soil water and N concentration, and soil characteristics (e.g. bulk density, organic carbon, parameters for a water-release curve). Cultivar differences, if known, can be incorporated by changing the input parameter file. Validation results and sensitivity analysis suggested six modifications that should improve model realism and predictions. Most of the modifications are easy corrections of simplified algorithms. SPIKEGRO integrates aboveground development and growth of individual plant components into one simulation. The model is useful in estimating development and growth throughout the growing season, and in predicting all stages of shoot apex development critical in scheduling cultural practices.