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 numerical system is used to represent the development of wheat plants starting from 1. 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