4-Pasture species composition

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Manipulate pasture species composition in each pasture zone for best possible pasture growth and quality

Guidelines to manipulating pasture composition

This procedure assists you to assess the current pasture base, outlines what improvements can be made and when to consider introducing new species.

Recognise the most important perennial and native pasture species

A wide range of pasture types are found across southern Australia including:

  • mainly native perennial grasses with some annual legume (eg sub clover)

  • annual grasses and legume-based pastures

  • sown exotic perennial grass pastures and annual or perennial legumes.

Avoid costly resowing by ensuring nutrient and grazing practices support persistence of existing desirable species

For each pasture type, species composition and productivity can be manipulated using combinations of fertiliser application, grazing management and strategic herbicide application, which can avoid resowing. Manipulating pasture composition by establishing new species is expensive. It can take up to 10 years to breakeven on the capital invested.

The key to manipulating pasture for long-term sustainable production is to understand the special needs of both native grasses and improved perennial based pasture types and to use grazing systems that will encourage and maintain their productivity. It is important to recognise the perennial and native pasture species that suit your environment. Become familiar with their growth characteristics so that grazing management can be used as a tool to improve pasture growth and quality.

The management principles and special requirements of native-based and improved perennial pastures are presented in 'Chapter 6: Making the most of native pastures', and 'Chapter 7: Improved perennial pastures' of the MLA publication, Towards Sustainable Grazing: The Professional Producer’s Guide. Chapter 8 of this publication deals specifically with grazing management for higher productivity within the whole farm system.

Use grazing systems that will encourage and maintain pasture productivity

It is well known that improving the perennial base of pasture can significantly increase livestock production per hectare. But to achieve this higher productivity, perennial pastures must receive the appropriate nutrients (see Procedure 3) and grazing management (see Module 3: Pasture utilisation) to ensure persistence and stocking rate must be increased to match the higher production of these pastures.

Improving the management of your existing pastures can improve growth rate and quality without the significant cost of replacing species or cultivars.

Assess the species present in your pasture and the percentage of total pasture they make up (eg % grasses, clovers, weeds and bare ground). Consider the proportion of desirables and undesirables on your property, to determine whether the composition can be improved through management (eg addition of fertiliser – see Tool 2.9) or better grazing management (see Module 3: Pasture utilisation). You may also need to consider the higher-risk, higher-cost alternative of resowing some areas.

Improve pasture management to avoid resowing

Assess composition of pasture zones

Use Tool 2.7 to assess the existing pastures across all significant pasture zones identified on your farm. Collect additional information on new and alternative pasture species, including their seasonal growth patterns, animal nutritional and production values and any environmental constraints. Seek advice from a local agronomist and gather information on the major pasture species that can improve your pasture productivity.

Manipulate the species mix to achieve the right pasture composition

Calculate the areas (estimated in total hectares) of all productive pasture groupings. Use this to assess the balance of species and growth patterns across the farm and through the various seasons. This assessment needs to be made against the normal seasonal rainfall pattern and variability (completed in Procedure 2). Local temperature extremes also need to be considered. Assess pasture composition against the guidelines for minimum and maximum recommended limits in Tool 2.7.

If your assessment indicates that the current pasture composition is unlikely to achieve best possible pasture growth and quality in any of the major zones, across the farm or throughout certain growth seasons, consider the following actions.

Take corrective action if pasture composition is inadequate

  1. Where practical, change management to bring pasture composition within desired limits by:

  • grazing or cutting to increase plant tillering. Using high density, short-term grazing or cutting to prevent undesirable annual grasses from reseeding and maintaining perennial grass and clover cover to limit germination of annuals in autumn (follow the grazing management tactics to increase, maintain or decrease individual species in Tool 2.11)

  • addressing soil health and soil fertiliser content for the most responsive and desirable species (see Tool 2.9)

  • tactical using herbicides to control weeds (eg low chemical rates in a spray-graze operation to stop seeding or higher rates of selective or non-selective herbicides to kill targeted weeds); low rates of chemicals applied over prolonged periods may result in target weeds becoming resistant

  • allowing desirable pasture species to recruit through setting and dropping seed before grazing or cutting. Note that this is not effective for some species, such as phalaris

  • improving pasture growth rate, quality and persistence

  • extending the spread of desirable plant growth patterns where there is sufficient soil moisture to sustain growth or introduce deeper-rooted species to improve access to nutrients and soil water

  • encouraging species diversity in and across all pasture zones

  • improving pasture performance in unfavourable conditions, such as more tolerant species for acid soils where liming is not economical or practical.

  1. When cost-effective management practices do not achieve best possible pasture productivity, consider establishing perennial species and cultivars that are proven to improve capability. Aim to achieve:

  • improved pasture growth rate, quality and persistence

  • extended spread of desirable plant growth patterns where there is sufficient soil moisture to sustain growth, or introduce deeper rooted species to improve access to nutrients and soil water

  • species diversity in and across all pasture zones

  • improved pasture performance in unfavourable conditions, such as more tolerant species for acid soils where liming is not economical or practical.

Conduct economic analyses to determine the marginal returns on investment, cash flow implications and priorities before any significant expenditure is made to introduce new pasture species (refer to Module 1: Setting directions for the appropriate methods).

What to measure and when

See Tool 2.7 for the methodology required to assess pasture composition. You should check:

  • identified plant species and, for each species, its frequency and relative (%) contribution to total pasture mass

  • proportion (%) of perennial grass, annual grass legumes, weeds and bare ground in each paddock.

Measurements are best taken early in periods of high growth. Identification of some species is easier once seed heads have formed. Perform all measurements initially and measure annually in pasture zones selected for monitoring.

Further information

Commonly used pasture terms

Annual pasture – Pasture that only has annual grasses and legumes present. Many annual pastures were never sown to these species, they simply volunteered or invaded.

Electrical conductivity (EC) – A measure of the degree of salinity (total salt content) of water or soils. Electrical conductivity increases as salt content increases.

Evapotranspiration – The sum of water evaporated from the surface of vegetation (living and dead) and from the soil, and the transpiration of water through plants (pasture and trees).

Groundcover – Green, dead and litter material plus dung.

Improved pasture – Pasture that has been sown to exotic perennial grasses (eg phalaris, cocksfoot, fescue, perennial ryegrass, kikuyu) in combination with annual or perennial legume (sub clover or white clover).

Native pasture – Pastures consisting predominantly of native grass species, but with varying amounts of volunteer annuals. Most native pastures are ‘naturalised’ in that they contain varying proportions of native perennial grasses and introduced species, and may have been ‘top dressed with super and sub’ to introduce a legume component.

Pasture zone – An area of land that possesses physical characteristics significantly different to adjoining areas. It either presents opportunities, or requires different land use, pasture species or grazing management, to achieve best possible production across total pasture and crop land and throughout seasons.

Plant-available water capacity (PAWC) – Defines the amount of soil moisture readily available for uptake by pasture roots. It represents the fraction of soil moisture accessible to the plant within the root zone (not tightly bound to clay molecules). This fraction is the difference between the levels of water held in the soil at field capacity (fully wet) and wilting point (plants are unable to extract sufficient moisture to support growth below this level).

Water use efficiency (WUE) – A ratio that measures the efficiency of use of rainfall. Rainfall is lost through run-off, evaporation before use by pasture plants, sideways movement in the soil profile or deep drainage below the root zone. Any of these losses lowers the water use efficiency. Water use efficiency is expressed as the ratio of total growth of pasture (kg DM) over a given period to rainfall received (mm). Only consider water use efficiency as a measure to compare performance within a locality when soil type, rainfall pattern and other factors are similar.