1. General Model Information

Name: Pasture Quality Model

Acronym: PQ_MODEL

Main medium: terrestrial
Main subject: pastoral,agriculture
Organization level: Organ, Organism
Type of model: compartment model, ordinary differential equations
Main application:
Keywords: grazing, pasture, cattle, sheep, reproductive growth.


Dr Simon Woodward

AgResearch Ruakura, Private Bag 3123, Hamilton, New Zealand
phone: +64 (07) 838 5914
fax: +64 (07) 838 5117
email: woodward@iname.com


Simon Woodward


This is a differential equation model of tissue flows in perennial grass-dominant pasture designed to optimise stocking and water management for maximum summer-autumn milk production. The model consists of five plant tissue categories: vegetative green leaf and sheath, reproductive green leaf and sheath, green reproductive stem, mature reproductive stem, and dead material. Flows between the tissue categories are described mechanistically, and the dependence of various parameters on season, temperature and moisture is emphasised. Several of the model components have already been described in detail in published papers. The finalised model form is currently being refined. A paper is being prepared which summarises the entire model and illustrates its use by comparing predicted supply of quality summer-autumn pasture for dairy cows under contrasting stocking rate and water application strategies.

II. Technical Information

II.1 Executables:

Operating System(s):

II.2 Source-code:

Programming Language(s):

II.3 Manuals:

II.4 Data:

III. Mathematical Information

III.1 Mathematics

Details of the functional forms can be found in the published papers below, or may be obtained by request to the author. Some of the information is commercially restricted.

III.2 Quantities

State variables:Pasture mass components (Leaf/sheath, dead, stem, standing dead) measured in kgDM/haRate processes:New growth, senescence, decomposition, going reproductive, grazing, stem maturation, trampling.

III.2.1 Input

Required weather data:Daily total irraddiance and sunshine hoursDaily rainfallDaily mean 10cm soil temperature

III.2.2 Output

Rates of change of the state variables.Predictions of intake components per animal.

IV. References

Woodward, S.J.R. (1997) Dynamical systems models and their application to optimising grazing management. In Peart, R.M. & Curry, R.B. (eds) Agricultural Systems Modeling and Simulation. Marcel Dekker, New York, 419-474.

Woodward, S.J.R. (in press) Formulae for predicting animals^ daily intake of pasture and grazing time from bite weight and composition. Livestock Production Science. (Accepted February 1997).

Woodward, S.J.R. (in press) Bite mechanics of cattle and sheep grazing grass-dominant swards. Applied Animal Behaviour Science. (Proof-checked September 1997).

Woodward, S.J.R. (in press) Modelling photosynthesis and growth of individual components in a reproductive grass pasture canopy. Functional Ecology. (Submitted August 1997).

Woodward, S.J.R. (in press) Mechanisms of leaf and tiller death in grazed perennial ryegrass swards. New Zealand Journal of Agricultural Research. (Submitted August 1997).

Woodward, S.J.R. & McCall, D.G. (in prep) A dynamical model for control of post-reproductive pasture quality using water and grazing management. Agricultural Systems. (To be submitted).

V. Further information in the World-Wide-Web

VI. Additional remarks

This is a dynamical systems model for intensively grazed temperate zone improved pasture systems. It's goal is to provide a theoretical systems understanding and also predictions suitable to real farm applications.It's construction is heavily influenced by the work of I.R. Johnson, A.J. Parsons & J.H.M Thornley from England.It is also heavily influenced by the New Zealand agricultural science knowledge base and is applied to New Zealand pastoral farming systems.It's formulation has been funded by the New Zealand Government through the Foundation for Research, Science and Technology. Information and remarks about the application of this model

Last review of this document by:
Status of the document: Contributed by Simon Woodward
last modified by Tobias Gabele Wed Aug 21 21:44:47 CEST 2002

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