Urea, at 46% nitrogen (N), is the most concentrated solid nitrogen fertiliser. This means there is less to freight and handle. It is also one of the most economical nitrogen fertilisers.

These factors have seen urea become the world’s most popular nitrogen fertiliser. Urea can be applied on its own, or in blends with products such as MAP and Muriate of Potash. It can be applied pre-plant, or in side dressing and top-dressing programs.

There are limits to how much urea can be safely applied at planting without harming germinating seeds or young seedlings. Urea is soluble. It can be applied in fertigation programs and as foliar sprays. Urea is also used a non-protein nitrogen supplement for ruminants, e.g. sheep and cattle. Urea allows ruminants to make better use of low protein roughages, e.g. dry grass, during dry weather and the onset of drought.

MANUFACTURE AND SUPPLY Urea is a naturally occurring soluble organic compound. It is found in some moulds and fungi and in urine. The dark green growth responses in urine patches in poorly growing pasture and forage crops are often attributable to a response to nitrogen compounds such as urea. Urea is manufactured synthetically in large quantities around the world for use as a nitrogen fertiliser and in industry, e.g. resins and glues.

The first step in the manufacture of urea is to react natural gas, atmospheric nitrogen and water together at high temperature and pressure to produce ammonia (NH3) and carbon dioxide (CO2). These gases are then reacted at high temperature and pressure to produce urea

[CO(NH2)2]. 2NH3 + CO2 → CO(NH2)2 + H2O

Incitec Pivot Limited manufactures urea in Brisbane, using natural gas from south west Queensland. This product is sold into northern New South Wales and southern and central Queensland. To supplement local production, urea is imported through various ports along the eastern and southern seaboards. Various grades of urea are available.

Granular Urea has good storage and handling characteristics, and being a granular product, its particle size is more evenly matched with that of other granular fertilisers, such as DAP, MAP and Gran-am, and coarse crystalline grades of Muriate of Potash. This minimizes segregation when used in blends.

Urea is incompatible in dry blends with ammonium nitrate based fertilisers, e.g. Cal-Am, and also superphosphate. Prilled Urea Prilled urea has a smaller particle size than granulated urea, making it quicker to dissolve. It is preferred where urea is applied in solution (dissolved in water), e.g. in fertigation programs, foliar sprays, and the preparation of stock licks (non-protein nitrogen supplements for ruminants).

Prilled Urea is imported into north Queensland, and is available ex Mackay, Townsville and Cairns. An alternative product, Stockfeed Urea, is available, ex Brisbane. This product is obtained by screening undersized granules from the granular urea that is manufactured on site.

Low Biuret Urea Low biuret grades of urea, containing less than 0.4% biuret, are used in foliar sprays in high value horticultural crops and where urea is sprayed repeatedly at high rates. Granular grades of urea for soil application typically contain up to 1.5% biuret. Note. There is no need to use a low biuret grade of urea when formulating livestock supplements. Biuret is only of importance when urea is used in foliar sprays.