Simulating the effects of temperature and seeding depth on germination and emergence of spring wheat

Numerous models using constant thermal time have been used to predict the time required from seeding to emergence of spring wheat (Triticum aestivum L.). However, several researchers have questioned the theoretical validity of the assumption that the daily development rate is a linear function of temperature. In reality, the response of plant development rate to temperature is curvilinear. We developed a model to simulate seedling emergence of wheat using a nonlinear beta function to describe the developmental rate–temperature relationships over the full range of temperature (0–42 °C) for plant development. Three consecutive processes, i.e., germination, subcrown internode elongation, and coleoptile elongation, are involved during the period from seeding to seedling emergence. We considered each of these processes separately when simulating the combined effect of temperature and seeding depth on seedling emergence. Several well-defined data sets that are available in the literature were used to derive the model parameters. The model was independently tested with observed data obtained from controlled environments and from field experiments. Although the model described the full range of temperature, it was tested for the range from 0 to about 30 °C. Model predictions of the time required for seedling emergence agreed reasonably well with the observed times, although the model preformed better at higher than at lower temperatures. The root mean square error of the model prediction was about 2 days. All model parameters can be readily determined for a given cultivar from well-defined experiments conducted in controlled environments.