NBPT Urea (Protected Urea)
How it works
NBPT Urea is urea that is treated with an active ingredient known as urease inhibitor. Urease inhibitor can be either coated onto the outside of the fertiliser granule or incorporated into the urea granule melt during the manufacturing process. Urease is the enzyme which catalyses the conversion of urea to ammonium. It is during this process that ammonia gas is lost from ordinary urea. The urease inhibitor acts as a blocker to the active site of the urease enzyme, moderating the rate at which urea converts to ammonium, and as a result, reducing ammonia losses and retaining more effective N to grow grass.
NBPT Urea can be spread throughout the growing season, at times when many farmers would otherwise spread calcium ammonium nitrate (CAN) or ordinary urea. Weather conditions are also an important factor to consider when applying any type of fertiliser N. During periods of drought, it is best to hold off on applying fertiliser N until rain is forecast and there is sufficient soil moisture for N uptake by the plant roots. This is due to the fact that if rain does not arrive to melt the fertiliser N into the soil, it will not be taken up by the plant and will remain in the soil until sufficient soil moisture is present.
Impact at Farm Level
NBPT Urea can have a positive impact at farm level in terms of financial benefits. NBPT urea is cheaper than CAN on a cost per kg of nitrogen basis. While it may appear slightly dearer than ordinary urea, it will give the same “effective N” for the plant as urea, at a 13.0% lower spreading rate due to more of the N retained.
NBPT Urea can also result in more grass being grown over a longer period of time, resulting in +0.5t DM/ha over ordinary urea. While the quantity of grass grown by using CAN, NBPT urea and urea was similar across all fertiliser types in the short-term. A long-term trial at Johnstown Castle Research Centre showed that the grass grown by the fertiliser, net of the zero N control, for NBPT urea was greater than standard urea in 6 out of 7 years. 2018 was an exception due to drought when water was the limiting factor not nitrogen. NBPT urea grew 13% more grass on average compared to ordinary urea. The additional yield is similar in magnitude to the extra effective N level delivered to the plant by NBPT urea over ordinary urea. CAN yielded 9% more than ordinary urea.
Another big advantage of NBPT urea is that farmers can use it throughout the permitted growing season. It will work as effectively as ordinary urea in spring in damp conditions and, due to the inclusion of the urease inhibitor, it releases N slower and more effectively than during the growing season. Trials at Johnstown Castle showed that weather conditions, for example, dry bare soils, conducive to loss of N were encountered in the springtime (March) of the year. Therefore, it is recommended to apply NBPT urea in springtime to reduce N losses. In addition, NBPT urea is a key technology for Ireland to reduce ammonia losses and is accounted for in the national inventory to reduce national ammonia emissons.
An example of NBPT Urea being used to great effect can be seen at Kildalton College’s farm.
Benefits to the Environment
Nitrous Oxide (N₂O)
There are several reasons why NBPT Urea is seen as beneficial, none more relevant than the environmental impact of using it. Nitrogen fertilisers release nitrous oxide (N₂O) which is a powerful greenhouse gas emitted from agriculture. Teagasc studies show that NBPT Urea has 71% lower N₂O emissions, this while also having comparable ammonia losses to CAN. NBPT urea can also be seen to reduce ammonia loss by up to 79% in comparison to ordinary urea. NBPT urea also consistently yields as well as CAN in Irish grasslands.
NBPT urea helps to reduce nitrate (NO₃) leaching. Nitrate leaching can occur during times of heavy or prolonged rainfall. Free draining soils are particularly susceptible to losses as nitrate is very mobile in soil and can be readily leached to groundwater. CAN is made up of 50% ammonium and 50% nitrate. After spreading CAN a large pool of nitrate is placed in the soil. It is open to being leached away if unfavourable conditions occur, such as heavy rainfall events.
NBPT urea converts to the ammonium form of nitrogen when applied to soil. Ammonium is more stable in soil than nitrate and less susceptible to leaching due to its positive charge. Soil microbes convert ammonium to nitrate almost like a steady conveyer belt; plants take up both nitrate and ammonium as required for growth and have access to a steady flow of available nitrogen as soon as the NBPT urea granules begin to melt.
Protected Urea delivers lower emissions at a lower cost.
What do farmers need to do?
Farmers are encouraged to switch from ordinary Urea and CAN to NBPT Urea. In order to do this, there are some considerations to make in terms of application preparation and where to purchase NBPT urea products. There are over 20 NBPT urea products available from at least six fertiliser blenders. There are standard N options, N plus sulphur (S) options, as well as N plus potassium (K) plus S options.
New farmers should also consider what compounds are required to use with NBPT Urea, with straight phosphorus (P) and K fertilisers or blends such as 0-7-30 or 0-10-20 needed to achieve a 100% switch. Alternatively, farmers would need to use an application or two of high P-K products such as 18-6-12 plus S based on farm fertiliser requirements. This opens the opportunity for more straight N slots where NBPT urea with or without S is a good fit. If in doubt, farmers can check utilise a variety of resources here.
In 2024, a new formulation of NBPT urea will include P in fertiliser blends for the first time. This ensures the stability of the NBPT inhibitor while delivering a reliable fertiliser option to reduce N₂O and ammonia emissions from fertiliser N.
Other Considerations
Other factors for farmers to consider when using NBPT Urea include:
- Choosing a product that has larger and stronger particles.
- Avoiding spreading on very windy days.
- Ensuring the correct fertiliser settings/calibrations and bout width are used, which can be determined by using a spreader manual, phone app or online resources.
- Using simple tray tests to verify the evenness of the spread pattern.
Find more information on Fertiliser Spreaders and Calibration here.
Frequently Asked Questions
| Question | Answer |
|---|---|
| Can Protected Urea be applied after lime? | Where NBPT urea is being applied, trial work indicates that it is safe to apply to fields that have been limed recently. |
| Why use Protected Urea in the first or second round of fertiliser in the springtime? | It is low cost, reduces N losses, is a safer form of N in terms of leaching and denitrification, and is the number one technology to help Ireland reach national ammonia inventory targets. |
| Will it work as fast as CAN or standard urea? | Yes. It is a more stable and efficient form of N compared to other major N sources. |
| Will NBPT urea give the same performance as CAN fertiliser applied in dry conditions? | Yes, the Irish trial results show no significant yield or N recovery difference between CAN and NBPT (urease inhibitor). |
| Is NBPT urea more corrosive on fertiliser spreaders? | It is more hygroscopic than other fertilisers, causing it to draw moisture if the spreader is not washed out. |
| What’s the shelf life of NBPT urea? | Manufacturers recommend to use within six to 12 months depending on product type. Consult a fertiliser supplier for more information. |
| How stable is the NBPT Urea when mixed with other nutrients? |
NBPT urea is most stable when bagged as a straight N product. Its stability in storage may differ when bagged with other nutrients as follows:
|
| Will NBPT urea affect soil microbes? | Trial work conducted at Johnstown Castle indicates no negative impact on soil microbes (grassland plots that have received protected urea for over eight years). Trials show positive impacts on soil biological communities compared to controls |
| Will NBPT urea affect water quality or get into waterways? | No, NBPT urea is less likely to be leached through soil compared with CAN, but farmers still need to adhere to good practice guidelines when applying fertilisers. |
| Is NBPT urea regulated? | NBPT urea is regulated by the EU and Irish regulatory bodies. |
| Is there a risk of the NBPT getting into the food chain? | Irish and international studies have demonstrated that no residues were found in the milk of cows grazing pastures fertilised with NBPT urea. |
Testimonials
“It was probably one of the easiest fertilisers to calibrate in the spreader, and that is taking into account that my machine can be hard to get right. Also, I got a lot further with a full spreader. And it is also cheaper per unit of N than CAN.”
– Sam Pierce, Suckler Beef Farmer, Wexford.
“After hearing about NBPT urea at discussion group meetings, we decided to try it out and we have been happy with the results. NBPT urea, low-emission slurry spreading (LESS) and reducing chemical N use are the low-hanging fruit when it comes to GHG emissions. These tools are a great initial step in reducing our carbon footprint as an industry.”
– Cathal and Des McHugh, Dairy Farmers, Roscommon.