Use of protected urea to reduce emissions

Using protected urea can reduce emissions of greenhouse gases and ammonia.

Urea is a popular fertiliser choice on UK farms, measuring up well on price per unit of N compared to other products. However, after application, some of the N content can be lost to the atmosphere as ammonia through volatilisation, or nitrous oxide (N₂O) directly through nitrification or indirectly through ammonia.  

Ammonia emissions from urea are thought to make up 9.9 % of the total UK agricultural ammonia emissions (based on 2022 data). Ammonia loss to the atmosphere reduces the N content of the applied urea by 10–30%.

Protected (or stabilised) urea contains a urease inhibitor that can limit those losses by slowing the conversion of urea to ammonia. Urease inhibitors do not stop ammonia emissions but prevent them by increasing the window of opportunity for N to be taken up by the soil. There are several urease inhibitor types in use, with N-(n-butyl) thiophosphoric triamide (NBPT) the most common.

While protected urea is more expensive than standard urea on a per tonne basis, it is cheaper on a per kilogram of N compared to CAN and standard urea.

Studies have shown that protected urea can reduce ammonia emissions by around 10-50% in various conditions compared to standard urea. Protected urea is a safer form of N in terms of leaching and will reduce nitrous oxide by up to 70% compared to CAN. In short, you can get double benefit of reduced ammonia (meaning more N remains in the soil for crop and grass use) and lower levels of nitrous oxide release (meaning lower GHG emissions).

In arable crops, the reduction in ammonia volatilisation associated with protected urea can potential lead to improved nutrient use efficiency (NUE) and higher crop yields. By minimising nitrogen losses through volatilisation, a greater proportion of the applied N remains available for plant uptake, supporting better growth and improved yields.

Similarly, the use of protected urea in grassland management can potentially lead to improved yields. Grasses are highly responsive to nitrogen application, and by reducing nitrogen losses through volatilisation, more N remains available to support grass growth, resulting in increased  forage production.  

It is important to select an inhibitor that maximises NUE while also supporting soil health and promoting optimal crop and grass yields. Efficacy claims must be proven and verified by either the companies supplying protected urea, or by those selling the inhibiting product for adding to products on-farm.

When released, ammonia can mix with other gases in the air to form fine particular matter. This can travel long distances and, when inhaled, can have a negative impact on human respiratory health. With the potential to reduce ammonia emissions, protected urea can have a positive impact on air quality and thus can benefit human health.

Using best management practices reduces the risk of ammonia losses from both protected and unprotected urea, such as effectively incorporating or injecting urea fertiliser into the soil.

Losses can also be minimised if urea is applied when soils are moist (not wet) or when rainfall is expected.

For use with liquid fertilisers, inhibitors can be bought separately and added to the tank at the time of application.

When changing to using protected urea, it is advisable to consult a FACTS qualified adviser or extension service in your region for the most up-to-date and region-specific information.

• Since April 2024, farmers in England can only apply unprotected solid and liquid urea (urea that does not contain a urease inhibitor) between 15 January and 31 March. This is when ammonia losses are negligible due to colder, wetter conditions
• From 1 April only protected urea in solid form can be used. Unprotected liquid urea can be used from 1 April if there is an agronomic justification provided by a FACTS-qualified farm personnel or adviser
• Compliance is overseen by Red Tractor through farm inspections demonstrating responsible fertiliser use
• In Northern Ireland, Scotland and Wales, fertiliser containing urea (solid and liquid) can be applied as per the relevant legislation
• Check latest assurance scheme standards for specific requirements for when fertilisers containing urea should be protected/inhibited to deliver ammonia reduction