Nutrients are applied to a pasture for a number of reasons. It can be to correct a nutrient deficiency, maintain or improve soil fertility but primarily the focus is to increase production of a pasture.
Many farmers that grow crops select the fertiliser according to the crops nutrient requirements and selecting a fertiliser for a pasture is no different. The selection of a pasture fertiliser should be based on the nutrient needs of the pasture plant and the grazing animals. Fertiliser needs to be applied if the soil does not have sufficient nutrients for the pasture to establish and grow and is also required to replace what has been removed by the grazing animal to maintain paddock production.
A good starting point is checking to see if there is good history of fertiliser usage and this is best achieved by undertaking a soil test.
Where a paddock has good soil fertility it may not respond to applications of fertiliser. In these situations, the application of fertiliser is made to maintain the soils fertility by replacing the nutrients removed by grazing animals (via meat and milk), cutting of hay and silage and the removal of a seed crop.
Nitrogen (N) - Nitrogen is the most common fertiliser used to increase pasture production and this is mainly applied by the product called Urea. When applying nitrogen to pastures, it is important to consider the following factors such as; that the pastures need to be actively growing, that the soils should not be waterlogged and that the fertiliser is best applied within three days of grazing or slashing. (NSWDPI, 2006).
Phosphorus (P) - Phosphorus is frequently a limiting nutrient to the growth of pastures. Phosphorus fertilisers can be applied to dry soil and split applications are preferable when using heavy rates. Highly productive temperate pastures require a soil test Colwell P of at least 75 mg/kg, for medium production the result should be 50 mg/kg (NSWDPI, 2006). Having low Colwell P levels may create favorable conditions for weeds and less productive pasture plants therefore limiting pasture production.
Potassium (K) - A large store of potassium is available in most soils. Potassium deficiency usually arises when plant removal is high. Hay and silage production removes large amounts of potassium from the soil. Potassium is relocated around the farm in dung and urine and should be replaced in areas of depletion. (NSWDPI, 2006).
Sulphur (S) – Sulphur can be the forgotten nutrient as many fertilisers have small amounts available. Single superphosphate is the most common fertiliser to supply sulphur to pastures and Gypsum supplies sulphur and calcium (Ca) to the soil.
Depending on how nutrients are removed determines how much and what type of fertiliser needs to be applied to maintain production. Nutrients removed from paddocks through milk by dairy cows are different to those removed by wool production or live weight gain in sheep and beef.
Good pasture production requires good soil fertility and achieving this means applying fertilisers that have the correct nutrients for the pasture you are growing and that replaces the nutrients removed by your farming system.
For more information please contact our Stephen Pasture Seeds or AusWest Seeds team.
Incitec Pivot, 2011. http://www.incitecpivotfertilisers.com.au/en/Products%20and%20Services/Agriculture%20Industry/~/media/Files/Productive%20Pastures%2012pp%207870proof12.ashx
University of Georgia