Process-based modeling of temperature and water profiles in the seedling recruitment zone: Part II. Seedling emergence timing

• Soil temperature and water were used to successfully predict seedling emergence.
• Simulated thermal time and hydrothermal time were similar to measurements.
• Simulations averaged across depth had marginally quicker emergence timing for wheat.
• Recruitment depth over simulated time for spring wheat was similar to measurements.
• Simulated hydrothermal time models improved little upon thermal time models.

Predictions of seedling emergence timing for spring wheat are facilitated by process-based modeling of the microsite environment in the shallow seedling recruitment zone. Hourly temperature and water profiles within the recruitment zone for 75 days after planting were simulated from the process-based Simultaneous Heat and Water (SHAW) model using local and non-local microclimatic data. Linear mixed-effects models indicated that simulated thermal and hydrothermal time accumulations were similar to measurements. Emergence timing was fitted using the Gompertz equation. Simulations averaged across depth had quicker emergence timing of wheat at inflection by 20 °Cd for thermal time and 23 MPa°Cd for hydrothermal time models, equating to 1.3 days earlier in the DAP model. Seedling emergence rates were similar between simulations and measurements. Simulations for emergence timing with hydrothermal time improved upon thermal time only at the soil surface. The recruitment depth of spring wheat over time was fitted with a Beta function which was positively skewed with early recruitment of a large number of seedlings from a moderate depth and late recruitment by a small number of seedlings from a shallow depth. The time of simulated Beta maxima was greater by 39 °Cd for thermal time and 3 MPa°Cd for hydrothermal time, and 1.5 days less than the measured maxima for the DAP model. The 95% confidence intervals for the fitted simulation and measured Beta functions overlapped for the entire duration of the distribution for all time scale models. Process-based simulations of soil temperature and soil water in the seedling recruitment zone provided representative predictions of seedling emergence timing for spring wheat.