Home Pasture and Fertiliser Nitrogen fertilisers

Nitrogen fertilisers

Written by Dr Clive Dalton
What does Nitrogen (N) do?
  • It acts as a growth promoter in plants.
  • It’s the easiest and usually the cheapest way to grow more feed.
  • It makes plants look green and lush.
  • It promotes leaf growth.
  • Deficient plants look pale green, stunted and turning to yellow.
Which fertilisers supply nitrogen?
  • Urea
    • Is very soluble
    • Only contains nitrogen (46-0-0-0)
  • Sulphate of ammonia or ammonium sulphate (21-0-0-24)
    • Is very soluble
    • Contains some sulphur along with the nitrogen
  • DAP (di-ammonium phosphate) which is 18-20-0-2
    • Soluble
    • Compound fertiliser that contains Phosphorus and Sulphur as well as Nitrogen.
  • MAP (mono-ammonium phosphate) which is 11-22-0-1
    • Soluble
    • Compound fertiliser that contains Phosphorus and Sulphur as well as Nitrogen.

When should you apply nitrogen?

  • Use it “strategically” - or when you are guaranteed to get a response and make money.
  • There must be sufficient soil moisture and a warm soil (above 6C) to get a good response.
  • You get best response (80-100%) in spring and early summer.
  • You’ll get 60-80% response in late winter and early spring.
  • In autumn expect 20-40% in autumn when rainfall is low and 50-70% when rainfall was high.
How much should you put on?
  • Remember what you get free from the air via a good clover crop. Figures vary a bit but 200kg N/ha/year would be middle of the range of values.
  • Remember the concern for the environment and limits suggested by Regional Councils. For example one council suggests a maximum of 150kg N/ha/year from whatever sources you use.
  • For grazed pasture 20-40 kg N/ha (45-90 kg Urea/ha)
  • For silage and hay 30-60 kg/ha (65-130 kg Urea/ha)
  • Higher levels will result in leaching into the soil and the soil water. This will be worse in winter.
Management tips
  • Apply N fertiliser when there is some pasture regrowth.
  • This would be about 1600-1800 kg DM/ha or 50mm long or above.
  • Graze about 4-5 weeks after application if growth has been good.
  • Cut for silage or hay 5-6 weeks after application.
  • The trick is to predict when you expect a feed deficit and apply it well in advance.
  • Check your spreader to make sure it is delivering the correct dressing.
  • Keep well away from waterways and drains when spreading.

Footnote. The composition of fertilisers is always in the order of N-P-K-S-Mg