Ammonium Nitrate Vs Urea

Ammonium nitrate is a source of nitrogen containing half its nitrogen in the ammonium form and half in the nitrate form. Some properties are set out in comparison with urea in the following table. Ammonium nitrate has an advantage over urea in that it can be topdressed onto the surface of the soil and left uncovered without a danger of loss of nitrogen to the atmosphere. When urea is left uncovered on the surface of the soil losses of nitrogen occur through volatilisation of ammonia during the hydrolysis of the urea. Such losses with ammonium nitrate are only likely to occur on highly calcareous soils. The loss from urea can be largely avoided if the urea is covered with a layer of soil e.g. by topdressing in front of the seeding tines or discs. Also there is not likely to be much loss from the urea topdressed onto the soil surface if the application is followed closely by heavy rain which will wash the urea into the soil. On the other hand freight will be a little higher for ammonium nitrate because of its lower nitrogen content than urea