Chemical fertility - soil nutrition
Two major groups of nutrients are needed for optimal soil health and pasture production:
- major or macronutrients - phosphorus (P), sulphur (S), nitrogen (N) and potassium (K), calcium (Ca) and magnesium (Mg)
- micro-nutrients - iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), cobalt (Co), selenium (Se) and chlorine (Cl)
Other nutrients may be absorbed, but are not essential for plant growth.
The two most important elements for pasture systems are phosphorus and nitrogen. Both are not only critical for pasture growth, but are also implicated in serious environmental concerns where nutrients leave the target site.
Phosphorus is the major factor associated with nutrient pollution (and subsequent algal blooms) in waterways, and nitrogen is the major driver of soil acidification.
To get the most out of pastures and fertilisers, carry out regular soils test to identify key nutrient requirements, and know how these nutrients (particularly the macro-elements) move through the soil, pasture and animals.
Plan optimal fertiliser rates for each paddock with higher priority given to:
- pastures with high proportions of more productive species (usually these will be sown grasses and legumes)
- paddocks with deeper soil
- paddocks with a favourable aspect where growth is greater later in spring
Consider soil pH and mineral status when making fertiliser decisions.
The intensification of livestock production through pasture improvement, fertiliser application and increased stocking rates has had significant on-site and off-site impacts on the environment at paddock and catchment scales.
Such impacts include:
- increased productivity and profitability
- soil acidification
- contamination of surface and sub-surface water from nutrient-enriched run-off
- degradation or loss of remaining remnant vegetation
- increased deep drainage, thus greater risk of dryland salinity
