Urea 46: a nitrogen fertiliser used worldwide
Urea 46 is the most used nitrogen-based fertiliser worldwide in terms of tonnes due to its high nitrogen content. Industrially synthesised from ammonia and carbon dioxide, the finished product in the form of granulated or prilled urea contains the elements carbon, oxygen, hydrogen and nitrogen.
The gradual mineralisation of this product thanks to the enzymes in soil bacteria means that it is widely used as nitrogen-based fertiliser to ensure crop yield in spring. Indeed, the slow release of nitrogen in the form of ammonium provides gradual nutrition to crops.
Traditionally positioned on corn crops, the use of granulated urea has also expanded to wheat crops in recent years, even among farmers in France who generally hold strong to the use of ammonium nitrate.
Urée 46: energy-consuming production
Combining ammonia and carbon dioxide to obtain urea 46 granules requires high pressure (150 bars) and a temperature of up to 180°C. These production conditions make urea 46 the source of nitrogen that consumes the most energy per unit of nitrogen produced.
The price of urea on the global market therefore depends on trade between major supplier and consumer countries, but also on the price of the fossil fuels used.
Urea 46: release of nitrogen and volatilisation
It is recommended to bury granular urea when using it on crops to limit nitrogen loss through ammonia volatilisation. Indeed, hydrolysis by bacteria enzymes in the soil transforms urea nitrogen into ammonium and is accompanied by the release of ammonia gas into the air.
This loss of nitrogen is one of the reasons for the loss of efficacy of urea nitrogen compared to ammonium nitrate, per unit spread.
Limiting nitrogen volatilisation, but at what cost?
To ensure optimum results from nitrogen-based fertilisation through urea 46 input, some suppliers have put in place a granulated urea solution treatment: urease inhibitors.
These chemical substances prevent the natural activity of microorganisms and their enzymes and slow down the transformation of urea into ammonium.
As it inhibits the effective functioning of the microbial metabolism, this controversial treatment is still undergoing extensive testing, although the product is already on the fertiliser market.
The use of urea in the face of issues
Urea remains the most used nitrogen-based fertiliser worldwide, as it is easy to produce and generally remains the least costly nitrogen unit on the market.
However, divergent views as to its effectiveness and current global issues such as the protection of water and air quality, reduced energy consumption through the transformation of co-products and protection of the biological fertility of soils advocate for a transition to another model.
Tackling these challenges and ensuring greater respect for soils require a shift to more natural practices and the use of more virtuous eco-fertiliser products.