Nitrogen - Fact sheet
Calcium Ammonium Nitrate (CAN 27% N): Major straight N product, Contains calcium. The form of N is 50% Nitrate [NO
3
] and 50% Ammonium [NH
4
+ .]. The calcium will help reduce acidifying effects of ammonium.
Urea: Contains 46% N. Ammonium is positively charged, clay particles are negative charged, and therefore urea is held by clay particles provided moisture is present.
Cost per kg N (Jan 2013) – CAN €330/t 270kg N = €1.22c / kg N
– Urea €450/t 460kg N = €0.98c / kg N
Urea - Prills vs.
Granular: Prills are small and soft, granular is larger and harder making it more suited to blends. Prills are suitable up to 12m spread widths; granular is suitable up to 18m spread widths.
Plant uptake of N: Plants take up N either as Nitrate - N and/or Ammonium - N.
Ammonium is more easily taken up in cold weather.
Urea versus CAN: Urea is a cheaper source of N and but requires soil moisture to avoid being lost to air by ammonia volatilisation.
Volatilisation : Loss of ammonia (NH
3
) gas to the atmosphere. Increases when soils are dry, high temperature (>12°C) and high pH or freshly limed soils.
Urea in summer: Urea needs moisture to be converted to ammonia.
CO (NH
2
)
2
+ H
2
0 + urease 2NH
3
+ CO
2
. At high temperatures there is rapid conversion of urea to ammonia; lack of moisture will prevent ammonium being held by the soil.
Denitrification: Nitrate is converted to Nitrogen (N
2
), Nitrous Oxide (N
2
O) or
Nitric Oxide (NO) which is lost to the atmosphere. Soil bacteria cause this process when soil is wet or waterlogged.
Mineralisation: Soil contains a reservoir of N that can be as high as 7,000 kg/ha.
Most of this is tied up in organic matter. Following microbial action in the soil, some of this N is made available in a form that can be taken up by the grass roots. The average quantity of this background-N made available is approximately
145 kg N/ha/year.
Leaching: Nitrate is water soluble and may be lost by leaching (percolates down through soil) or by surface run-off (sloped land).
Fertilizer N and Slurry: Slurry applied on fertilizer N creates ideal conditions for denitrification, i.e., anaerobic conditions and high carbon compounds. Leave 7 days between spreading either slurry or artificial N fertiliser to reduce the risk of N loss.

Nitrogen and frost: Ideally N applications in frosty conditions should be avoided as there is the risk of N loss through run off when soils thaw and also N fertilisers may remain on the soil surface leading to N loss through volatilisation
Urea & Lime : Lime increases soil pH which increases rate of volatilisation of ammonia. Do not spread urea for 3-6 months after lime application.
N fertiliser and heavy rain: Nitrogen can be lost as nitrate by either run-off or leaching
How quick is N available: Once fertilizer N is applied, it is not all taken up at once, it is taken up over a period of 4 to 8 weeks after application. Nitrate is available immediately for plant growth. Urea takes 2/4 days to convert to ammonia provided moisture is present.
Nitrogen in Slurry and lime: Lime increases soil pH which increases rate of volatilisation of ammonia. Do not spread slurry on recently limed soils and leave
3-6 months between lime and slurry applications.
Response rates to applied Nitrogen
Jan – Feb:
March:
April
June
– May:
– August:
0 – 10 kg Grass Dry matter per kg N applied.
0
– 25
15
– 50
15 – 35
September: 15 – 25
Response rates will vary from year to year due to temperature, sunshine, rainfall, ground conditions, type of grass sward, reseed or not, etc
Soil pH & Nitrogen: Maintaining a soil of pH 6.3 – 6.5 will improve N recycling and release from soils. Soil maintained in the optimum soil pH range can release
60 to 80kgN/ha on an annual basis.
Fertiliser Spreaders and application rates: Calibrate fertiliser spreaders as fertiliser batches change. Check evenness of spread by tray test and calibrate to ensure correct application rate. Set up correctly on the tractor - spreader is set even from side to side, level back to front and set at correct operating height.
N in slurry: N in slurry behaves similarly N in urea. To maximise the recovery of
N from slurry apply in the spring time under cool, moist conditions. Typical N recovery with splash plate application in the spring is 25%. Summer application with splash plate 5%
Splash plate V’s Trailing shoe & N recovery: Trailing shoe application method will approximately increase the N recovery by 10% over the splash plate application method for spring (25 v 35%) and summer (9 v 18%) application timings.