Module 7: Grow more pasture
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Introduction
Introduction1 quiz -
Grow more pastureBuilding and maintaining soil fertility
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Grazing to keep the desirable species productive and dominant
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Establishing new pastures1 quiz
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SummaryConclusion1 quiz
Grazing to keep the desirable species productive and dominant
MLA & AWI July 16, 2024
The way a pasture is grazed has a major bearing on the species that survive and dominate. Grazing strategies can be developed to maintain the desirable species and optimise their growth rates. Different grazing methods can also be used in more of a tactical, or short-term way to manipulate the composition of degraded or weedy pastures, reducing the need for herbicides or costly renovation.
The way a pasture is grazed also affects how evenly nutrients in dung and urine are distributed and recycled throughout a paddock. Sheep camps can be minimised and maintenance nutrient requirements can be reduced with the appropriate grazing system.
Understanding how desirable species grow helps when planning a grazing system that will encourage these species to become more dominant. Likewise, knowing the weak spots in a weed’s lifecycle helps when planning grazing tactics to decrease their level in a problem paddock.
To aid in persistence, knowing when desirable plants are most vulnerable is key to protecting them. Annual plants are most vulnerable during establishment and flowering (seed set is critical for survival) and perennial plants are most susceptible following dry periods and during reproduction (where they set up for summer survival). The Grazing management guidelines provide more information about matching plant growth and grazing management.
Establishing an effective process of grazing management is about tailoring the principles outlined in the guidelines to meet the business’s goals. There is no ‘right’ grazing management and considerable flexibility is needed to continually re-balance the needs of soil, pasture and animals.
There are three critical actions required to keep desirable species productive and dominant:
- Assess pastures to determine if the current grazing system is limiting the growth and persistence of desirable species. A number of pasture assessment techniques are described in the Pasture assessment techniques tool. For mixed pastures (annual or perennial) based on introduced species, a good composition is: 60% desirable grasses, 30–40% clover and 0–10% weeds. In native grass-based pastures, the optimum clover content is 20% or less.
- Clarify the particular requirements of the species in the pasture, especially those targeted for increase or decrease and apply the appropriate grazing management as outlined in the Grazing management guidelines. Most pastures are quite a complex mixture of species and individual compromises for each paddock will be required.
- Measure, manage and monitor the impact of any actions on pasture composition. Monitor and record paddock management actions and changes in pasture composition using MLA’s Pasture Paramedic or Pasture Health Kit. Ensure any actions (e.g., changed grazing pressure, fertiliser rates, tactical herbicide use, etc.), maintain or increase the proportion of desirable species in the pasture.
Shoots and roots
There is a general tendency among plants to maintain a relationship between root and shoot dry weight. When leaves and stems are removed by grazing, the plant compensates by lowering root growth and returning to a ratio characteristic for the plant. So, in short, continuously grazed grasses or ones maintained at one leaf stage will have small root systems like those on the left of the photo below, while pastures that are grazed and allowed to recover three live leaves look more like the plant on the right-hand side. Plants also have other feedback mechanisms in regulating shoot and root growth involving hormone control, such as the cessation of shoot growth, when roots are under drought stress, low soil temperature or poor aeration from waterlogging or compaction.
Pasture rest periods
All perennial species are more productive and persistent under grazing that includes rest periods between periods of grazing. Rest periods are necessary to replenish root reserves used to grow shoots and leaves during grazing (this is especially true for perennials such as lucerne) and complete reproductive phases. Growth rates of annual grasses such as annual ryegrass can also be improved by rest but their persistence in a pasture depends on seed-set during spring, rather than survival of individual plants during summer.
Deferred grazing
Deferred grazing is a tactic where livestock are excluded from pasture areas after the break of season to aid grass recovery and maximise germination and establishment of pasture seedlings. Sheep can be concentrated into containment areas, ‘sacrifice’ paddocks or laneways and supplementary fed. Containment areas and sacrifice paddocks should have low erosion risk. Pay extra attention to animal health. The length of deferment should be governed by pasture growth but, to achieve the best outcomes for both the pasture and animal welfare, grazing is best deferred until pasture has achieved:
- a minimum of 500 kg DM/ha for dry sheep
- a minimum of 1,000 kg DM/ha for single bearing ewes or 1,200 kg DM/ha for multiple bearing ewes (during late pregnancy).
- a minimum of 1,200 kg DM/ha for single bearing ewes or 1,500 kg DM/ha for multiple bearing ewes (at the point of lambing or in lactation).
Pasture residues after grazing
The more green material (pasture residue) left after grazing, the faster the regrowth, as photosynthesis is more quickly restored. During the growing season it is ideal to leave about 1,000 kg DM/ha (green material), but this also depends on animal class, species and leaf number. If 1,000 kg/ha cannot be left post grazing then place a higher priority on significant rest periods to encourage regrowth.
Seedling recruitment
Some pastures, such as perennial ryegrass, cocksfoot and prairie grass, recruit from seedlings and this is a tactic that can be used on pastures with less than desirable plant numbers. Steps include:
- removing stock to allow the grasses to set seed during spring
- running a big mob of stock in a paddock during summer when the seed is ripe to ensure the seeds are knocked to the ground and dead pasture is eaten off to 1,000–1,500 kg DM/ha by the autumn break
- resting pasture after the autumn break to let new seedlings establish.
Seedling recruitment tactics for phalaris and tall fescue have not proven successful based on poor seedling vigour.
Native grass seedling recruitment occurs using deferred grazing strategies to allow seed set and build up soil seed reserves provided pasture composition consists of at least 5–10% of native grasses.
Recruited perennial ryegrass seedling in centre.
Source: MLA