GerminatingPhase

The GerminatingPhase represents a phenological sub-phase within a plant’s developmental timeline, responsible for simulating the transition from sowing to germination. It defines the conditions under which a seed germinates and completes the phase once those criteria are satisfied. Typically, it spans from the Sowing stage to the Germinated stage, and its completion is determined by either environmental triggers (soil moisture and temperature) or a user-specified germination date.

Overview

The GerminatingPhase models the transition from sowing to germination in the crop’s phenological development. Germination is assumed to occur on the day after sowing, when any of the following conditions are met:

  • Soil water at the sowing depth exceeds the lower limit (LL15),
  • Soil temperature at the sowing depth is greater than or equal to the minimum soil temperature (as defined by the MinSoilTemperature child function),
  • A specific germination date is provided via the DateToProgress property.

Once any of these conditions is satisfied, the seed is considered germinated, the SeedImbibed event is raised, and the simulation advances to the next phenological phase.

Model Structure

This section describes how this model is positioned within the APSIM framework. It outlines the broader structural and computational components that define its role and interactions in the simulation system.

This model inherits structural and functional behaviour from the following core APSIM components:

Connections to Other Components

This section describes how the model interacts with other components in the APSIM Next Generation framework.
These connections allow the model to exchange information—such as environmental conditions, developmental stage, or physiological responses—with other parts of the simulation system. For a general overview of how model components are connected in APSIM, see the Connections Overview.

Component Model Connection Type Description
SoilPhysical IPhysical Link, First Available Provides soil physical properties including layer thickness and lower limit (LL15) values.
WaterBalance ISoilWater Link, First Available Supplies current soil water content for each layer.
Plant Plant Link, First Available Provides sowing depth information from the plant’s sowing data.
Phenology Phenology Link, First Available Manages phenological stage transitions and timing.
Clock IClock Link, First Available Provides current simulation date and time information.
SoilTemperature ISoilTemperature Link, First Available Supplies soil temperature at each layer.
MinSoilTemperature IFunction Child, By Name Defines minimum soil temperature threshold required for germination.

Model Variables

This section lists the key variables that describe or control the behaviour of this component. Some variables can be adjusted by the user to modify how the model behaves (configurable), while others are calculated internally and can be viewed as model outputs (reportable). For a general explanation of variable types and how they are used within the APSIM Next Generation framework, see the Model Variables Overview.

Configurable and Reportable Properties

Property Type Description
Start string Phenological stage at which this phase begins (e.g., Sowing).
End string Phenological stage that marks completion of the phase (e.g., Germinated).
IsEmerged bool Boolean flag indicating whether the crop has emerged above the soil surface (i.e., this phase is happening above ground). Default is false.

Read-Only Reportable Properties

Property Type Description
ProgressThroughPhase double Accumulated units of thermal time as progress through phase. Set to 1 when germination occurs.
Target double Thermal time target to end this phase. Always 1 for this phase.
FractionComplete double Fraction (0–1) indicating how much of the phase is complete. Returns 1 when germination has occurred.
DateToProgress string Data to progress. If set by external model, phase will ignore its mechanism and wait for the specified date to progress.

Events

This section describes the events associated with this component. Events are signals or notifications that indicate when a particular process occurs within the simulation, or when a component needs to respond to a change in another part of the system. Some events are listened for by this component to trigger its processes, while others are raised to inform other components about changes. For a general overview of how APSIM Next Generation uses events to coordinate processes between components, see the Events Overview.

Events Listened For

These are signals or notifications that the GerminatingPhase listens for from other parts of the simulation:

Event Purpose
PlantSowing Indicates when the plant is sown, allowing the phase to determine the soil layer depth where seeds are placed. This is essential for checking soil conditions relevant to germination.

Events Raised

These are signals that the GerminatingPhase sends out to notify other components when actions occur:

Event Description
SeedImbibed Raised when germination occurs, signaling other models or processes to begin their activities related to the germinated seed.

Processes and Algorithms

This section describes the scientific processes and algorithms represented by this component. Each process corresponds to a biological, physical, or chemical mechanism simulated during a model time step. Where appropriate, equations or conceptual summaries are provided to explain how the process operates within the APSIM Next Generation framework.

Germination Triggers

Germination occurs in one of two ways:

  1. User-defined germination date

    If DateToProgress is specified, germination occurs exactly on that date, regardless of soil moisture or temperature. The phase completion is determined by:

    \[ \text{proceedToNextPhase} = \text{Phenology.checkIfCompletionDate}(\text{startDate}, \text{Today}, \text{DateToProgress}) \]

  2. Environmental conditions at sowing depth

    If no date is defined, germination is triggered when all of the following conditions are met:

    • The current day is not the sowing day:

    \[ \text{!phenology.OnStartDayOf("Sowing")} \]

    • Soil water content exceeds the lower limit (LL15) for the sowing layer:

    \[ \text{SWmm}[\text{SowLayer}] > \text{LL15mm}[\text{SowLayer}] \]

    • Soil temperature at sowing depth meets or exceeds the minimum required value:

    \[ \text{SoilTemperature}[\text{SowLayer}] \geq \text{MinSoilTemperature.Value()} \]

Sowing Depth Determination: The sowing layer is determined using the value of plant.SowingData.Depth, which maps to the appropriate soil layer index through the SoilUtilities.LayerIndexOfDepth function.

Phase Progress

When germination conditions are met: - The SeedImbibed event is raised - ProgressThroughPhase is set to 1 - propOfDayToUse is set to 1 (indicating the full day is used) - The phase proceeds to the next phenological stage

Phase Reset

The ResetPhase() method resets all phase tracking variables to their initial states: - DateToProgress is cleared - startDate is set to minimum value - ProgressThroughPhase is reset to 0 - fractionCompleteYesterday is reset to 0

User Interface

GerminatingPhase can be added as a child of a Phenology node in the model tree. Right-click the Phenology node, select “Add Model…”, and search for GerminatingPhase in the Filter Box.

See Also