ZadokPMFWheat

The ZadokPMFWheat model calculates Zadoks growth stage values (Zadoks, Chang, and Konzak 1974) for wheat based on the current phenological growth stage within the simulation. This model provides a standardized way to express wheat development stages using the internationally recognized Zadok scale.

Overview

The Zadoks scale (Zadoks, Chang, and Konzak 1974) is a numerical system (0-99) used to describe the growth stages of cereal crops, particularly wheat. The ZadokPMFWheat model translates APSIM-NG’s internal phenological stages into equivalent Zadok values, enabling researchers to communicate development stages using familiar agricultural terminology and facilitating integration between modeling and field observations.

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
Phenology Phenology First Available Provides current growth phase, stage progression, and fraction completed within phases.
Plant Plant First Available Supply plant is alive and today’s DaysAfterSowing.
TillerNumber IFunction Child Connection Total number of tillers the plant will develop.
HaunStage IFunction Child Connection The current Haun stage of the plant.

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
TillerNumber IFunction Total number of tillers the plant will develop.
HaunStage IFunction The current Haun stage of the plant.

Read-Only Reportable Properties

Property Type Description
Stage double Current Zadok Stage value
StageDAS double Days After Sowing for specific Zadok stage when it first occurs. Example usage is StageDAS(51).

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.

Early Vegetative Development (Zadok 00-19)

The ZadokPMFWheat model calculates the Zadoks growth stage (\(Z\)) based on the current phenological phase of the wheat plant. Different calculation methods are applied depending on the developmental phase.

Germinating Phase:

In Germinating, Zadoks Stage (\(Z\)) is 5 times the fraction of the germination phase completed (\(F(t)\)):

\[ Z = 5.0 \times F(t) \]

Emerging Phase:

In Emerging, Zadoks Stage (\(Z\)) is calculated as 5 plus 5 times the fraction of the emergence phase completed (\(F(t)\)):

\[ Z = 5.0 + (5.0 \times F(t)) \]

Tillering and Stem Extension (Zadok 10-39)

Before the phenological stage reaches 5.3 during StemElongating phase, Zadoks Stage (\(Z\)) is calculated as 10 plus the Haun stage value (\(HS\)):

\[ Z = 10.0 + HS \]

Reproductive Development (Zadok 30-90)

After the phenological stage reaches 5.3, Zadoks Stage (\(Z\)) is determined through linear interpolation between predefined growth stages and their corresponding Zadok values:

APSIM Growth Stage Zadok Stage Growth Stage Description
5.0 30.0 MaximumSpikeletPrimordia
5.99 34.0 Fourth node detectable
6.0 39.0 FlagLeafAppearance
7.0 55.0 HeadEmergence
8.0 65.0 Anthesis
9.0 71.0 MaximumGrainLength
10.0 87.0 EndGrainFill
11.0 90.0 HarvestRipe
Figure 1: APSIM to Zadok Growth Stage Mapping

At HarvestRipe stage, Zadok stage is fixed at 90.0.

User Interface

ZadokPMFWheat 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 ZadokPMFWheat in the Filter Box.

References

Zadoks, J. C., T. T. Chang, and C. F. Konzak. 1974. “A Decimal Code for the Growth Stages of Cereals.” Weed Research 14 (6): 415–21. https://doi.org/10.1111/j.1365-3180.1974.tb01084.x.