Pasture growth forms the basis of productivity in grazing operations. It is important for producers to understand the key factors affecting pasture growth when seeking to maximise production from improved pastures.
By understanding pasture growth, producers are able to maximise pasture utilisation, one of the key profit drivers, while also maintaining good land and pasture condition.
Phases of pasture growth
Pasture growth is usually described in three phases, followed by a fourth phase where pastures have 'hayed-off'
By understanding these phases, producers are better able to optimise pasture utilisation. The figure above shows the changes in pasture quality and yield as pasture ages. Animal production can be increased by grazing pastures during phases 1 and 2 as quality is high. Quantity can, however, be limiting during phases 1 and 2 and animal intake may be constrained.
Limiting grazing in early phase 1 will assist subsequent growth - continued grazing during this period will slow pasture growth and limit production.
Conversely, pastures in phase 3 will yield well, but be of reduced quality.
Improved pastures may be a monoculture (one species), but usually consist of a mix of species including annual and perennial grasses and legumes. In grazing improved pastures, it is important to be aware of the plant mix and the lifecycle of each species. Grazing strategies that preserve the species balance by avoiding grazing at critical growth stages for particular species, such as at establishment and the reproductive stage for annuals, can then be adopted.
Overgrazing during critical growth periods, such as early in phase 1, can deplete the plant reserves and root biomass of perennial species, reducing their persistence particularly during dry periods. Dry periods will also affect the growth of annuals, often reducing the growing season and with it, the nutritional value of the pasture.
Stocking rates should be adjusted to match feed on offer as this changes with seasonal variations within years and between years. Plans should be put in place to respond to changing conditions and seasonal variability before pastures are overgrazed with potentially permanent affect.
One of the characteristics of pasture rundown, caused by overgrazing, is the removal of palatable species, particularly perennials, and the introduction of weeds. Where weed infestation occurs, often after prolonged drought, herbicides may be used to restore the pasture balance. Whenever using chemicals, producers should be aware of any grazing withholding periods (WHP) and be sure to follow labelling directions.
Feeding the soil
Good pasture growth not only stabilises soil through root growth, but also promotes other favourable soil characteristics by increasing soil organic matter levels which in turn increases water filtration and soil nutrients. Legumes will also contribute nitrogen to the soil which will promote grass growth.
Improved pastures are typically more productive than the native pastures common to a particular area. This production is dependent upon factors, such as soil fertility, and to realise an improved pastures' full potential, the application of fertiliser is usually required.
Soil and plant tissue tests can help determine what is required in a fertiliser. The timing of the application is also important and local advice from the department of primary industries, a consultant or fertiliser supplier who is accredited with FertCare can help determine application timing for a particular situation.
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