Effective Nitrogen Source
A five-year experiment conducted by Incitec Pivot on the northern plains of New South Wales (see graph) highlighted the similarities between the performance of urea and Big N.
When applied at the same rate of nitrogen, both products produced similar ammonium-N concentrations in the soil and comparable growth rates.
Before plants can use BIG N or urea, the nitrogen they contain must be converted into nitrate-nitrogen (the most common plant available form of nitrogen).
BIG N in the soil
When BIG N is applied to the soil it diffuses into a cylindrical area surrounding the point of application. This ammonia retention zone is not uniform in concentration. It is highest at its point of release and diminishes with increasing distance from this point. Soil pH follows the same pattern with soil pH being highest at the point of release.
When it is applied to the soil, BIG N ionises from ammonia to ammonium. Ammonium is a cation with a positive electrical charge and is attracted to negatively charged substances such as clay and organic matter to form a strong bond.
Nitrifying bacteria are attracted to the ammonium band in the soil. Nitrifying bacteria gain energy by breaking nitrogen-hydrogen bonds to form nitrate. Nitrification starts at the outside of the ammonium band and moves towards the centre, taking two weeks to a month.
The amount of nitrate produced depends on the amount of ammonium in the soil, not the number of nitrifying bacteria. This conversion occurs naturally in the soil and is the same process that allows plants to use mineralised nitrogen from organic residues and other nitrogen fertilisers.