GrassGro Questions and Answers

Does GrassGro work?
What enterprises does GrassGro simulate?
Where does GrassGro work?
Which pastures can GrassGro simulate?
Where do I get information about soils?
Who else uses GrassGro?
Is GrassGro the right tool for me?
If I buy GrassGro do I get GrazFeed?
What kind of problems can I solve with GrassGro?
Where does GrassGro keep it’s data and configuration files?

1. Does GrassGro work?

GrassGro can provide robust predictions of the variability in plant and animal production over many seasons or years. It is often the best estimate of the performance of a grazing enterprise that is available, given the incompleteness of information at a particular location. However, users should be aware that the accuracy of simulated pasture and animal outputs at a site depends on the accuracy of the inputs that describe the site’s weather, soil, pasture species, animals and management. Every effort should be made by the user to quantify the variability in these components at a location and to consider this variation when comparing GrassGro’s performance against measurements or farm records. Users should also check the predicted outputs for each part of a grazing enterprise carefully before analysing a management issue.

Before release, each version of GrassGro is thoroughly tested in 2 ways. One set of testing compares GrassGro predictions against data sets from grazing system experiments at several sites in temperate Australia. A second round of testing compares long simulations at mutiple sites for consistency and reasonableness over extended periods for which there are no experimental data. Results of these comparisons can be found in Publications

2. What enterprises does GrassGro simulate?

GrassGro simulates one enterprise at a time. Available enterprises are: an ungrazed system, a self-replacing or purchased flock of breeding ewes, a wether flock, lamb fattening, steer trading, a beef cow herd turning off several classes of young stock and a haycutting operation. Breed descriptions are specifed by the user for wool, meatsheep or dual purpose sheep and pure and crossbred breeds of British, European and Bos indicus cattle.

GrassGro offers the user considerable flexibilty in describing flock or herd structures and management systems but the user may also need to approximate actual livestock management to that available in GrassGro. GrassGro cannot adequately simulate mixed enterprises of ewe and wether flocks, sheep with cattle, fodder crops, mixed crop and livestock enterprises or grazing rotations in which animal movement is determined by pasture availability rather than time.

3. Where does GrassGro work?

GrassGro can simulate grassland systems in any location for which there is a complete set of weather inputs in an suitable format, a description of the soil and for which there is an appropriate pasture species available in GrassGro. The list of pasture species in GrassGro is not exhaustive but users are often able to select a comparable type of plant from those listed. Users have more scope to adjust descriptions of sheep and cattle breeds to match local types.

GrassGro can usually be readily applied to most sites with temperate pastures in southern NSW, Victoria, Tasmania, South Australia and Western Australia. GrassGro has been used successfully to simulate grassland systems in North America and Northern China. Currently GrassGro does not have available descriptions of native grass species, summer-active exotic grasses or specialist pasture cultivars such as tetraploid ryegrasses, and so its application is restricted to grazing systems without these species.

4. Which pastures can GrassGro simulate?

Several pasture species are available for selection by the user in GrassGro. Users are advised to check actual pasture composition and then to select the dominant species growing in a paddock. If a species or cultivar does not appear in the list the user chooses that which best represents the pattern of pasture growth and quality at a site.

The following species can be simulated either singly or in a mixture: Perennial ryegrass; Phalaris (Australian); Cocksfoot (Currie-type); Annual ryegrass (Wimmera); Early-flowering annual grass; 4 cultivars of Sub clover (Dalkeith, Seaton Park, Mount Barker, Leura); Medic (Paraggio); White clover; 2 types of Lucerne (winter-active and semi-winter dormant) and Capeweed.

Currently GrassGro does not have available descriptions of native grass species, summer-active exotic grasses or specialist pasture cultivars such as tetraploid ryegrasses, and so its application is restricted to grazing systems without these plants.

5. Where do I get information about soils?

While it is preferable to use laboratory measurements of soil physical properties, these can be expensive and not readily available. Default values in GrassGro for soil physical properties are estimated from Northcote classifications or texture classes. Remember that soils vary widely around these default values.
It is good practice when using a simulation tool like GrassGro to test a range of values for soil inputs and get a feel for the sensitivity of GrassGro outcomes to these numbers.
For sources of soil maps and surveys and relevant state government departments with information on soil testing laboratories see Useful links.

Dig a hole.
Taking a spade, crowbar and tape measure into a paddock and digging several holes is a direct way to obtain information about the variation in soil types in a paddock and to obtain values for the depth and texture of the topsoil and subsoil (A and B horizons).
If the holes are dug at the peak of spring, you can obtain a rough estimate of the rooting depth of plant species at the same time.
A protocol for sampling paddocks and soils for physical measurement is available in the Resource Kit

Here is a pdf document with parameters for some GrassGro sites: Soil Descriptions

6. Who else uses GrassGro?

GrassGro is used by a wide range of service providers to the grazing industries and grassland managers. These people typically need to understand how variability in climate affects pasture and animal production and the impact of management decisions on production risks in grazing enterprises. More than 300 users have been trained to use GrassGro since its release in 1997: researchers, private consultants, government advisors, policy makers, tertiary educators and farmers.
GrassGro is used in a variety of ways by consultants to evaluate land capability and management options in different regions and has been a key part of research programs, for example, in the Sheep CRC, the Bushfire CRC and in teaching “Systems Thinking” in agricultural education in Australia and overseas. For examples of how GrassGro has been used to analyse industry issues and investigate practical on-farm problems see Case Studies and Other Documents.

7. Is GrassGro the right tool for me?

GrassGro is for the thinking manager or investigator who is interested in making decsions using the best available science and information.
GrassGro helps you to understand how climatic variability affects pasture and animal production and economic outcomes over many seasons. The user can test the impact of management decisions on production for a range of sheep and beef grazing enterprises before spending resources.
Each analysis of an enterprise or grassland system is “tailor-made” because the user specifies the weather, soil type, pasture species and animal breed and management for their site. Typical issues that can be analysed with GrassGro are “What is the best long-term stocking rate for my farm?” , “What is the best lambing or calving date?”, “What is the value to my enterprise of adding a perennial grass?”, “What is the likely amount of pasture available to stock 6 months ahead?”, “What are the chances of these steers reaching target weights?”, “What are the costs and benefits to my enterprise if I destock this pasture to maintain pasture residues and prevent soil erosion?”
GrassGro will not make decisions for you but supports decision-making. It is a tool for planning, rather than a calculator or paddock recording system.
For examples of how GrassGro has been used to analyse industry issues and investigate practical on-farm problems see Case Studies and Other Documents.

8. If I buy GrassGro do I get GrazFeed?

No (and Yes!), GrazFeed is a separate tool that calculates the nutrient requirements of a single class of sheep or cattle at a time for one day. GrassGro analyses pasture and animal production and gross margin outcomes for a whole enterprise over many seasons (months or years).
However the animal model used in Grazfeed is also built into GrassGro. The right tool depends on the complexity of the problem you want to address.
For example, if you need to calculate the amount of wheat required over the next few days to feed Merino ewes in late pregnancy grazing short pasture you need GrazFeed.
Alternatively, if you want to assess the effect of a particular maintenance feeding policy for your ewe flock on the likelihood of crossbred lambs meeting market specifications for carcass weight over the long-term, then you need GrassGro.

9. What kind of problems can I solve with GrassGro?

GrassGro’s flexibility makes this a difficult question to answer concisely!
Users can test many practical and theoretical questions about how changes to any part of a grazing system or its management affect production and economic outcomes for a range of enterprises (see FAQ #2 above).
It’s important to realise that probabilities of particular outcomes are calculated in GrassGro from the variability in weather inputs, which are typically historical weather data. GrassGro does not use the Southern Oscillation Index (SOI) or other seasonal climate predictors. However GrassGro can be used to evaluate impacts of non-historical weather datasets, for example those generated to assess climate change scenarios. For examples of the way GrassGro is used see FAQs #4, #12 and #13 on this page.

GrassGro enables you to look at problems that have 2 different time frames:

1. Long (seasons or years)
Strategic planning typically requires evaluation over long time horizons in an attempt to assess the “best-bet” management system. In agriculture, enterprises with long biological lags, such as livestock breeding enterprises, provide limited opportunities for intervention. Once the management system has been designed and a key decision made, such as the date of mating, the manager must more-or-less live with the consequences of that decision. For example, a well-managed beef herd might have a 2-4 year lag between mating cows and the sale of steers from that mating.
In GrassGro this type of issue is examined with an historical analysis that simulates the enterprise over continuous sequences of, typically, 20-50 years.
Examples of strategic questions are: “What is the best long-term stocking rate for my farm?” , “What is the best lambing or calving date?”, “What is the value to my enterprise of adding a perennial grass?”
2. Short (weeks or months)
Tactical decisions are made over short time horizons in response to emerging seasonal conditions. These decisions typically attempt to maximise an opportunity or minimise a risk. An enterprise usually has a basic management calendar (derived from a strategic analysis) that has some scope for adjustment of timing, depending on the enterprise. For example, trading enterprises usually have shorter production lags and more flexibility than breeding enterprises. The manager of a lamb-fattening or a steer-trading operation can more easily vary the timing and number of animals to buy and sell to suit current conditions.
Because the planning horizon is short, the outcome of a tactical decision is usually heavily weighted by current conditions. The structure of a tactical question is along the lines of:
“Given the current state of this system (soil moisture / pasture / animal age and weight) what will happen over the next few months if I do… (nothing / change management)?”
In GrassGro this type of decision is examined with a tactical analysis.
Examples of tactical questions are: “What is the likely amount of pasture available to stock 6 months ahead?”, “Given the dry conditions prevailing, how much supplement should I buy to feed stock over the next 4 months?”, “Given the early start to the pasture growing season, what is the chance that these steers will reach marketable weights by mid-spring?”

10. Where does GrassGro keep it’s data and configuration files?

GrassGro uses a number of different type of data files.

Configuration files
Standard data files prepared by CSIRO
Data files that are customised by the user

Configuration files

Name	Location	Description
config.ini	{userappdata}\CSIRO\GrassGro{AppVerNo}	Main configuration file containing default user interface settings and default paths that specifies the location of many data files used in GrassGro. If you need to move the location of any regularly used data files (for backup procedures) you may need to edit this file.

Standard data files

Name	Location	Description
farmsystems.ggfl	{app}	Contains the standard Farm Systems.
library.gglb	{app}	Contains the standard Component library.
check.ggrp	{app}	Contains the standard Acceptability reports.
example.ggan example.ggan	{userdocs}\GrassGro {commondocs}\GrassGro	Working example of an analysis. Other example files may also be included. Also stored in the public documents area
issues.ggis	{app}	GrassGro Issues library.
locality.set locality.dx	{commonappdata}\grassgro	Contains the standard weather localities.

Custom data files

Name	Location	Description
custom_check.ggrp	{userdocs}\GrassGro	Extra custom Acceptability reports added by the user.
custom_library.gglb	{userdocs}\GrassGro	Main library of GrassGro components that are shown in the library tree.
farmsystems.ggfl	{userdocs}\GrassGro	Library of Farm Systems. Includes user’s additions.
custom_issues.ggis	{userdocs}\GrassGro	Extra custom GrassGro Issues added by the user.
*.met	{userdocs}\GrassGro\Weather	Weather files that have been unarchived off the CD.

Key

Key name	Location	Common name
{userdocs}	%my documents%	User’s My Documents directory
{app}	%program files%\GrassGro3	Application installation directory
{temp}	%temp%	User’s temp directory.
{commonappdata}	C:\Users\All Users	Common application data directory
{commondocs}	C:\Users\Public\Documents	Common documents directory
{userappdata}	C:Users\myusername\AppData\Roaming	Users application data directory
{AppVerNo}	3.3.10	Version number of the application

Further details can be found in datafile_user.pdf