Maximising pasture when season is short

WA research identifies how to maximise pasture when season is short

Australian Dairyfarmer News
RESEARCHERS: Western dairy researchers Peter Hutton (left) and Jessica Andony (right) meet with dairy farmer Matt Brett (centre) on Matt's farm at the site of the 2018 pasture trials, Dardanup WA.

RESEARCHERS: Western dairy researchers Peter Hutton (left) and Jessica Andony (right) meet with dairy farmer Matt Brett (centre) on Matt's farm at the site of the 2018 pasture trials, Dardanup WA.

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Western Australian dairy pasture research is delivering dividends and identifying key factors to maximise this valuable resource when in short growing seasons.

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Pasture is the key component of the dairy feedbase in Australia and Western Australia is no exception. The growing and grazing season for pasture in WA is typically from May to November and pasture is conserved mainly as silage in the spring months.

Annual ryegrass dominates the market because perennial ryegrass does not generally survive the dry summer and the majority of the dryland farms must be replanted each year.

The work by Western Dairy is focused on how farmers can maximise pasture production and utilisation in the relatively short growing season.

A trial site was set up at Matt Brett's farm at Dardanup, in the WA dairy region, a couple of hours drive south of Perth (see Figure 1).

FIGURE 1: A drone map of the West Australian Seed Productivity trials site.

FIGURE 1: A drone map of the West Australian Seed Productivity trials site.

The trials and demonstrations in 2018 included:

  • A seedmix trial of oats and ryegrass for early season production.
  • A grazing management demonstration affectionately called "the Goldilocks trial", to show the effect of getting the grazing "just right".
  • The second year of the WA seed performance trials (WASP). The trial site also included the testing of annual and Italian ryegrass lines for the Pasture Trial Network.

Seedmix trial

The seedmix trial looked at the question of whether an oats/ryegrass mix improved early season yields and persisted over the growing season.

Forage oats can be used in a pasture program to provide early season feed but have a shorter growing period than annual ryegrass.

A mixture of forage oats and annual ryegrass allows the strengths of one to cover for the weaknesses of the other to give a more even distribution of forage throughout the season.

In this trial, researchers included oats in a ryegrass mix to increase the early season dry matter production; and used a higher rate of ryegrass in an oats mix to increase the total season production relative to a lower seeding rate. They found that the oats/ryegrass mix increased the early season yield by nearly 700 kilogram of dry matter per hectare over the ryegrass monoculture (Figure 2).

FIGURE 2: Early season yield (cumulative of two harvests) of annual ryegrass and oats seed mixes (kg per ha). Columns with no common letter superscript differ significantly.

FIGURE 2: Early season yield (cumulative of two harvests) of annual ryegrass and oats seed mixes (kg per ha). Columns with no common letter superscript differ significantly.

They did not observe any increase in yield from a higher seeding rate whether it was in the seed mix or in the ryegrass monoculture. The work highlighted that it can be worth including fast-establishing pasture species in a ryegrass mix to chase early season production without compromising total season production.

The researchers plan to do more pasture trials in 2019 that will test a range of early-season species such as high-performance forage oats and ryecorn in a ryegrass mix.

WA Seed Performance trials (WASP)

The WA Seed Productivity trials (WASP) were developed by Western Dairy to provide farmers with the power to decide what ryegrass is best for their system. The distinguishing features of the WASP trials are:

  • Real time yields that are available on the Western dairy website.
  • A productivity index called the Milk Production Potential (MPP). The MPP ($/ha) compares ryegrass seed for its potential value to the farm business.

This is the second year of the WASP trials and this year the seed companies were on board to make the trials bigger and better. It is a terrific initiative that is producing some relevant information to the WA industry.

The significance of these trials is that Western Dairy can present results from independent and unbiased trials in what is a highly competitive and commercial seed industry.

The MPP $/ha is calculated as a value relative to Control 2018. Control 2018 is indexed as $0/ha and all other lines have a positive or negative index compared with it. The MPP calculation takes into account: energy yield (dry matter x metabolisable energy); energy requirements for milk production; milk price; feed utilization; and sowing costs. Email peter.hutton@westerndairy.com.au for details.

Seed lines are ranked by highest to lowest MPP and indexes are significantly different when they do not share a common coloured bar (see Table 1).

For example, in Table 1 Control fresh is significantly higher than Hogan but Abundant is not significantly higher than Hogan. Control fresh is the same ryegrass brand as Control 2018 but will be purchased each year to compare with the Control 2018 seed.

"Goldilocks" grazing

In 2018 researchers put into action the well-researched advice on best grazing management. The Project 30:30, which was overseen by Dairy Australia, identified ideal grazing management to maximise pasture yield and utilisation under rotational grazing.

Ideal grazing is between the 2nd and 3rd leaf stages, no more than 25 per cent of area experiencing canopy closure and results in a post-grazing residual of 4-6 centimetres. Leaving a post-grazing residual of 4-6cm optimises pasture productivity, nutritive value and persistency without limiting the intake by milking cows.

FIGURE 3: 'Goldilocks' simulated grazing (left) produced plants with adequate stem residual to maintain higher production relative to overgrazing (right).

FIGURE 3: 'Goldilocks' simulated grazing (left) produced plants with adequate stem residual to maintain higher production relative to overgrazing (right).

The research explains how to get grazing "just right" but researchers looked at the effect on production if grazing management is a bit off. They nicknamed the demonstration the "Goldilocks Effect" because they simulated overgrazing (residual of 3cm), undergrazing (residual of 8-9cm) or getting it just right (grazing at 2.5-3 leaves and a residual of 5-6cm). Researchers also included a treatment called "grazed too early" to simulate what can happen after a late break in the season, when pasture is immature, but conserved feed is in short supply. In this plot, the initial simulated graze was at the 1.5-leaf stage and a residual of 3cm with subsequent grazings to a residual of 5-6cm.

The simulated grazing at 2.5-3 leaves to a 5cm residual over the season produced (see Figure 4):

FIGURE 4: Simulated overgrazing and grazing before the 2.5 leaf stage early in the season reduced dry matter yield over the 2018 growing season.

FIGURE 4: Simulated overgrazing and grazing before the 2.5 leaf stage early in the season reduced dry matter yield over the 2018 growing season.

  • One tonne more of dry matter per ha compared to when the first grazing was too soon. Grazing too early in the season places stress on the plants that sacrifices later yields.
  • 0.85t more dry matter per ha compared to overgrazing to a 3cm residual. Overgrazing depletes plants of carbohydrate reserves in the leaves and roots resulting in a slower recovery.

This was a demonstration that did not have the robustness of a scientific experiment. However, the results support the findings of well researched work that advocates for getting grazing management "just right".

This story first appeared on Australian Dairyfarmer

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