Making More from Sheep Australian Wool Innovation Limited Meat & Livestock Australia
MODULE 7: Grow More Pasture
Tool 7.6
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Pasture composition

This method can be used to assess the frequency of both individual species (eg, phalaris) and species groupings (eg, perennial grasses).

  • Cut a 30cm length of 1cm-thick dowel, and drive a nail into one end
  • Throw the stick ahead at random intervals while walking across the pasture
  • After each throw, identify and record the pasture species or species group that is touching or immediately below the nail head at the end of the thrown stick
  • Repeat 20 times (depending on the evenness of the pasture)
  • Add the number of hits for each species or group and multiply by five (to convert to number of hits out of 100) to give % frequency (or composition)
  • Normal groups used are perennial grasses, legumes, annual grasses, weeds and bare ground
  • PROGRAZE® manuals include an example of a recording sheet that simplifies and speeds up the collection and recording process.

Perennial grass establishment and persistence

Counting the number of perennial grasses per square metre is a good way to assess:

  • How well the grasses established
  • How well the sown grasses are persisting.

To measure plants/m2, make up a quadrat (25 x 25 cm metal square). The technique involves throwing the quadrat 20 times across the paddock and recording the number of perennial plants inside the quadrat. Work out the average number of plants recorded inside the quadrat. Multiply results by 16 to convert to plants/m2.

Pastures will recover with careful grazing management if you have 5-8 perennial plants/m2. Tool 7.5 will help you choose the most appropriate grazing management strategy for your pasture.

Groundcover

Groundcover includes existing pasture, weeds and other herbage as well as litter. To estimate groundcover, stand in a representative part of the pasture with your feet 30cm (a foot) apart. Picture a 30 cm square in front of you, and looking vertically into the pasture, estimate the percentage area covered by plant matter and litter. Tool 6.2 in Healthy Soils has photos of 20%, 40%, 70% and 90% groundcover to help you estimate groundcover in your pastures.

Walk over the paddock and repeat the assessment at about 20 random sites. Record and average the results to accurately determine the percentage of groundcover.

You can make up a 25cm x 25cm square (quadrat) out of fencing wire or metal rod to help with this. The size isn’t important but if you stick to 25 x 25 cm, you can use the same square to assess perennial plant densities.

Pasture mass and feed on offer (FOO)

Pasture mass and Feed on Offer are both terms used to describe how much pasture is present in a paddock. Pasture mass typically assumes 300 kg Dry Matter (0.5cm ) is unavailable to sheep, while Feed on Offer includes all above-ground plant material. Thus, estimates of pasture mass are lower than the same estimate of FOO.

Pasture mass and Feed on Offer can be assessed by cutting, drying and weighing representative pasture samples as described in various State PROGRAZE® manuals. However, tools of varying levels of sophistication are also available which save much time in collection, and are considered to be the only practical method for use when day-to-day assessments are being made.

There are five types of tools available to measure pasture mass and feed on offer. [Cautionary note: these tools give an approximation only, and some tools (for example, tools 1 and 3 in the list below) can give misleading results when used on annual pastures that are highly variable in composition, in the early establishment phase of growth, or intensively grazed clover-dominant pastures in spring.]

1. Pasture rulers or ‘sticks’ that measure green pasture height (in cm) are simple, cheap and easy to use. Heights are easily converted to an estimate of kg green dry matter/ha via look-up tables. The MLA pasture ruler is included with hard copies of this manual. See signposts in procedure 7.2 to order your MLA pasture ruler.

Pasture density also needs to be estimated and used as a correction factor when growing or mature pasture is less than 100% of groundcover. See methodology for assessing groundcover and pasture composition (above) which can be used to estimate the percentage density of pasture. Moisture content will also need to be corrected for.

With experience, you can use the height assessment method to gain reasonably accurate estimates of mass, especially when periodically checked against assessments made by cutting and weighing.

2. Rising plate meters measure total pasture mass, green and dry standing feed, and are based on a plate that rises up a probe depending on the amount of compressed pasture material between the plate and ground. Pasture cuts need to be taken to calibrate the meter.

They are available from a number of commercial outlets, and price generally depends on the degree of automation of collection.

Rising plate meters are generally cheaper than electronic probes, and may be preferable when frequent automated assessment of pastures with significant levels of dry pasture is needed.

3. Electronic pasture probes measure dry matter of green material only. They are quick, easy to use and usually fully automated, including the capacity to directly download readings into office based computers. Some also allow collection of user-defined and read assessments such as groundcover and the plant shape, eg, flat, upright, etc.

Their accuracy declines if there is any free moisture present in the pasture, e.g. after rain or heavy dews.

They are normally the most expensive of the three groups.

Numerous commercially available meters and probes can be found on the internet (search for “pasture + meter”). Most rural merchandisers can also help locate commercially available models.

4. Photo standards for pastures are available, and give a good guide to the amount of Feed on Offer in a paddock. Visit www.lifetimewool.com.au/newpastures.aspx

Satellite imaging of weekly pasture growth by annual pastures can be found at: www.pasturesfromspace.csiro.au at either the shire level (free) or paddock scale (by subscription).

Pasture leaf stage

Assessment of leaf stage is made for target species and involves the examination of individual tillers from perennial grass clumps, or annual grasses. To count the number of new leaves on each tiller, inspect at least six plants across the paddock. Don’t count the remnant leaf — this is the portion of leaf left from the last grazing, and will be obvious as it will be the one with the tip eaten off. If the paddock has been evenly grazed, the assessment will be fairly straightforward. If the paddock was unevenly grazed, some plants will have more leaf material left behind after grazing.

Regrowth of a perennial ryegrass tiller indicating the correlation between leaf number and levels of water soluble carbohydrates stored in the tiller bases.

Source: Donaghy DJ, Fulkerson WJ (1999).  Optimum management of ryegrass-based pastures using plant regrowth stage.  Heritage Seeds Pty Ltd. Annual Communication Brochure.  13-16.

Note: the same principles apply to all grasses, but most perennial pasture species grow four live leaves rather than the three shown here for ryegrass. Many perennial tropical grasses grow six leaves.

Pasture quality

Assessment of pasture quality (energy content) normally requires full laboratory analysis. Field observations provide a useful guide to energy content in
MJ ME/kg DM.

Temperate Pastures

Actively growing green material is normally in the range of 11.0 to 12.0 MJ ME/kg DM.

Actively growing legumes normally have slightly higher energy content (+ 0.5 MJ ME/kg DM) than perennial grass.

Therefore pasture that is 100% green, has legume and perennial grass composition within the limits of 20 –30% legume and 60–70% grass and the oldest leaf of the dominant grass has not started to senesce can be assumed to have an energy content greater than 11.5 MJ ME/kg DM (M/D). Energy declines as temperate pastures mature.

Tropical Pastures

Tropical grasses mature and digestibility declines more rapidly than in temperate grasses. This means that the ‘window’ for moderate to high animal production is small without appropriate grazing management and may not be sustained for lengthy periods.

A guide to the decline in digestibility as temperate and tropical pastures mature.

Boschma SP, Lollback M, Rayner AJ (2010) Tropical perennial grasses - pasture quality and livestock production. Primefact No. 1070. (Industry & Investment NSW; Orange). Available at:

http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0011/360587/Tropical-perennial-grasses-pasture-quality-and-livestock-production.pdf