Nitrogen Management
- If the farm is stocked lightly; soils are low in nutrients/fertility (i.e. Olsen P < 12), and ryegrass content of pasture is low, then Nitrogen (N) fertiliser will not be an economic option for you - it could be cheaper to buy in feed to fill “gaps”.
- Inspect pastures to see whether urine patches indicate that pasture will respond well to N. Urine patches should be a darker green than surrounding areas and should display an obvious dry matter response relative to the rest of the pasture.
- Applying N to the whole farm could produce more pasture than is needed. Applying too little N may result in poor response or feed running short.
- Depending on the time of the year, N should be applied before feed shortage occurs (approximately 3-4 weeks for spring, 3-5 weeks for autumn, 4-8 weeks for winter). Ensure stocking rates are adjusted to utilise the additional food grown. Rank undergrazed pastures indicate wasted grazing opportunities and will limit subsequent pasture regrowth.
- N rates should not exceed 50-60 kg N/ ha in any single application. Maximum annual rates should not exceed 140-200 kg N/ha. High levels of N do have a negative effect on clover growth and will increase leaching into groundwater and waterways and contribute to greenhouse gas emissions.
- Where possible, choose paddocks that have a dense actively growing pasture to maximise N response. These are usually the paddocks with the best soil fertility. Apply N to pasture with a height of 4-8 cm (1300-1600 kg DM/ha) - this is when best responses are achieved, as there is sufficient leaf area to utilise limited sunlight (particularly in winter).
- N Fertiliser does not need rain to wash it into the soil. Most N fertilisers draw moisture from the humidity within the pasture and will dissolve into the soil within 24 hrs. N application from July-September should not be applied when high rainfall is predicted.
- N should be thought of as a supplement, not a fertiliser. This means N is only applied when there is a feed gap (Autumn-Spring), it may result in no N being used in a good year, but as much as 200 kgs in a bad year when feed is short.
- Usually N levels in pasture drop off to acceptable levels by 18-21 days after application. Do not graze 7-14 days after N application as levels are at their highest. Ideally apply N fertilisers 1-3 days after grazing to give plants as much time as possible to take up N before the next grazing.
- N can be applied before grazing (just before) but ensure immediate grazing occurs, since delaying it will result in very high nitrate levels in the grass.
- Avoid unimproved pastures, those dominated by weeds and waterlogged or poorly drained paddocks, as these will not be able to make the most effective use of applied N and may result in leaching and run-off occurring.
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