Phenology
The Phenology model in APSIM NG simulates the development of wheat plants.
Thermal Time
Daily Thermal Time is based on SubDailyInterpolation with three cardinal temperature and ThreeHourAirTemperature interpolation method.
Photoperiod
The daily photoperiod is calculated using the PhotoperiodFunction with 6 degrees twilight.
Phyllochron
The Phyllochron is the interval between the appearance of successive leaves on the main stem of wheat. It is determined by base phyllochron, leaf stage factor, and photoperiod effect.
The Haun Stage is defined as the number of leaf tips that have appeared on a cereal plant since emergence. It estimates from daily thermal time and phyllochron.
Stages and Phases
The wheat models outputs of phase names (Phenology.CurrentPhase.Name), stage names (Phenology.CurrentStageName) and decimal stage (Phenology.Stage) are consistent with the population culm development score (PCSD) as described by Celestina et al. (2023). Observations recorded following the protocole outlined by Celestina et al. (2023) are suitable for testing model accuracy and calibrating cultivar coefficients.
The stages are:
| Stage | Name | Description |
|---|---|---|
| 1 | Sowing | Seeds are planted in the soil |
| 2 | Germination | Seeds absorb water and begin to sprout |
| 3 | Emergence | Seedlings break through the soil surface |
| 4 | DoubleRidge | Formation of double ridges in the shoot apex |
| 5 | MaximumSpikeletPrimordia | Maximum number of spikelets is determined |
| 6 | FlagLeafAppearance | The last leaf (flag leaf) appears |
| 7 | HeadEmergence | Wheat head emerges from the flag leaf sheath |
| 8 | Anthesis | Flowering; pollen is released |
| 9 | MaximumGrainLength | Grains reach their maximum length |
| 10 | EndGrainFill | Grain filling is completed |
| 11 | HarvestRipe | Grains are mature and ready for harvest |
Phases are used to represent the development between two stages. The phases are:
| Order | Name | From | To |
|---|---|---|---|
| 1 | Germinating | Sowing | Germination |
| 2 | Emerging | Germination | Emergence |
| 3 | LeavesInitiating | Emergence | DoubleRidge |
| 4 | SpikeletsDifferentiating | DoubleRidge | MaximumSpikeletPrimordia |
| 5 | StemElongating | MaximumSpikeletPrimordia | FlagLeafAppearance |
| 6 | Heading | FlagLeafAppearance | HeadEmergence |
| 7 | Flowering | HeadEmergence | Anthesis |
| 8 | GrainExpanding | Anthesis | MaximumGrainLength |
| 9 | GrainFilling | MaximumGrainLength | End Grain Fill |
| 10 | GrainRipening | End Grain Fill | HarvestRipe |
| 11 | ReadyForHarvesting | HarvestRipe |
Other Reported Variables
In addition to reportable variables defined in all sub-models above, the phenology model reports several other variables that provide insights into the development of the wheat crop.