In view of the need to reduce greenhouse gas emissions, urea is many times seen as the most non-sustainable nitrogen fertilizer. The major reason is the carbon dioxide unity which is part of each urea molecule and which is set free during application. Furthermore, also ammonia and nitrous oxide emissions occur when urea is applied on the field.
This paper intends to provide another, or maybe better, and wider view on urea as nitrogen fertilizer with the target to promote and facilitate the discussion about the future of urea.
The conclusions of this paper are:
– Reducing greenhouse gas emissions is vital and nitrogen fertilizer products play a significant role, although the carbon footprint of just the production processes of nitrogen fertilizers is only a limited part of the total carbon footprint considering the complete life cycle. Improved farm practices and applying the already available technical solutions to increase the nitrogen use efficiency (inhibitors, coatings) can reduce significantly the carbon footprint of nitrogen fertilizers in general and urea more specific. On the other hand for smallholders using urea, advanced inhibition and application techniques is a challenge. Urea is and will remain a critical fertilizer into the foreseeable future with respect to provide food security for developing countries and in important crop systems like for example flooded rice fields, which lead to high ammonia losses and significant methane releases.
– Both urea as well as ammonium nitrate have their limitations when mixed with other materials. The misuse of ammonium nitrate-based fertilizers for terrorists’ purposes led to a variety of additional control measures.
– Ammonium nitrate has a lower nitrogen content than urea resulting in higher transportation, storage and application costs per ton of nitrogen for producers, traders, retailers and farmers.
– The increasing availability of low carbon ammonia resulting from the energy transition seems a perfect step towards low carbon ammonium nitrate based fertilizers. This is especially true for low carbon blue ammonia as limited investments are required. Low carbon urea can be produced by consuming carbon dioxide emitted by other sources. For smaller sizes more economical urea production process schemes are feasible when considering the production of fertilizers like UAN, UAS and urea based NPKs. Another benefit is the higher added value of these fertilizer products.
– Natural gas-rich regions are expected to remain big exporters of urea as these are focused to create added value to the available natural gas. Large investments are required to make the transition from natural gas and coal based nitrogen fertilizers to low carbon nitrogen fertilizers, which will require time as lifetimes of nitrogen fertilizer complexes are 40-50 years.