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Ammonium nitrate [photo] 

Ammonium Nitrate

The classic benefit of nitrate containing fertilizer

By Dr. Koos Bornman (General Manager: Strategic Agricultural Services)

It is well known that Omnia and its shareholders invested R1.4 billion in an additional nitric acid plant in Sasolburg. One pertinent reason for this is the fact that Omnia, as an agricultural company, realises the higher effectiveness of nitrate as nitrogen source, especially in the form of ammonium and calcium nitrate.

Many articles have been written to compare the effectiveness of ammonium nitrate and urea - each one emphasising a specific sales argument. In any case, the advantages of the nitrate form of nitrogen must be highlighted, for example minimum volatilisation; stimulation of root growth; stimulation of cation uptake; reduced acidification as a result of higher efficacy, improved water use efficiency, and more. The risk associated with the use of reduced nitrogen sources such as urea and ammonium also cannot be ignored. These risks include volatilisation loss, ammonia and ammonium toxicity and suppression of photosynthesis.

Omnia has done extensive research on the advantages of nitrate containing fertilizer and found that ammonium nitrate on average outperforms urea by at least 20% per unit nitrogen applied, where meaningful nitrogen response is obtained. To avoid bias in this article, deliverate reference is made to research by other institutions with variable interests, such as the local ARC (refer to SA Grain article May 2012), and also by Yara (the largest fertilizer manufacturer in the world. The latter markets both ammonium nitrate and urea based fertilizers.

Graph below shows the result of these institutions' research. This confirms that ammonium nitrate or LAN on average outperforms urea by between 26% and 40% per unit nitrogen, if it is top dressed close to the economic optimum on small grains or maize production for example. The graph also shows yield increases of between 5% and 10% if ammonium nitrate is applied at the optimum level of urea.


Relative efficiency of an ammonium nitrate based fertilizer source (LAN) vs. urea for grain production.

Most of Omnia's fertilizer is in granulated or liquid form and rich in nitrate, which ensure that the most is obtained from each unit of nitrogen without the threatening risk associated with the use of urea and ammonium sources. As an example of such risks, trial results of AECI (in the Western Cape) in the early nineties have already proven that a potential yield loss of between 5% and 25% may be expected with small grain production (depending on clay percentage) if urea instead of ammonium nitrate is top dressed.

Recent research also confirmed that nitrate improves water use efficiency and protects plants against heat and cold stress. The efficiency per unit nitrogen and water becomes increasingly important, especially if additional environmental factors are considered.

This article was published in the Nutriology® Newsletter (Summer 2012)