Understanding pasture for grazing
Most Queensland grazing land contains a mix of native and sown pastures.
Sown pasture and native pasture
Sown (introduced) pasture species were originally used for land that was cleared for grazing or as a replacement for native grasses that were considered far less nutritious for grazing animals. However, in more recent years, the true value of native grasses as pasture has been recognised.
Pasture composition varies considerably; however, 2 broad plant types are found in most pastures:
- perennials - live from 1 year to several decades
- annuals and weak perennials - live for 1 or a few growing seasons.
Pastures may also contain:
- forbs (non-woody broadleaf plants)
- legumes (plants like clover that can fix nitrogen into the soil)
- sedges (grass-like plants such as nutgrass)
- weeds (woody plants such as turkey bush that compete with pasture for nutrients, and plants like lantana that affect the stock carrying capacity of grazing land).
Features of healthy pasture
A healthy pasture is one that has a:
- high percentage of palatable, productive, perennial (3P) grasses
- small number of annual plants and weeds
- high frequency of desirable forbs such as native legumes
- variety of other favourable species.
Factors that influence pasture quality
Pasture quality and condition are affected by climate, soil type and grazing pressure.
Pasture growth is determined by a combination of rainfall intensity, ground cover, soil type and condition, evaporation, slope and tree cover.
Better quality soil leads to better quality pasture. Soil health has a direct impact on protein levels in pasture. Low soil phosphorus and nitrogen are the most common nutrient restrictions on pasture growth.
Other soil-related factors are the level of organic matter available (providing plant nutrients and helping to bind soil for better water infiltration) and the level of pasture cover. If ground cover level is at 40-50%, water runs off and there is greater risk of erosion. It is vital to manage pasture so that the top layer of soil (1-3cm) is preserved.