Protected Urea: How to Use It Well, and Why It’s Hitting Its Ceiling
Protected urea has become the default nitrogen fertiliser recommendation for Irish dairy farms over the past several years, and Teagasc has described it as a rare case of a new agricultural technology that costs less and delivers major environmental benefit at the same time. It works. But some cooperatives describe the interventions that got Irish dairy this far as approaching their ceiling, and protected urea is usually near the top of that list. Here’s how it actually works, how to apply it properly, what it delivers, and why “we’ve already adopted protected urea” is no longer enough on its own.
What protected urea actually is
Protected urea, sometimes called stabilised urea, is standard urea fertiliser coated with a urease inhibitor, most commonly N-(n-butyl) thiophosphoric triamide, usually abbreviated NBPT. Untreated urea loses a significant share of its nitrogen content to the atmosphere as ammonia through volatilisation, typically somewhere between 10 and 30% of applied nitrogen. NBPT doesn’t stop that loss outright. It slows the conversion of urea to ammonia, giving the soil more time to absorb the nitrogen before it can escape.
Agriculture is Ireland’s single largest source of greenhouse gas emissions, accounting for roughly 37.8% of the country’s national total as of 2023, driven mainly by methane from livestock and nitrous oxide from nitrogen fertiliser and manure management. Protected urea is considered a key technology for the sector in meeting Ireland’s target of a 25% reduction in agricultural greenhouse gas emissions by 2030, which is exactly why it became such a fast, widely adopted first move.
How to actually apply it well
Getting the environmental and agronomic benefit from protected urea depends on a few practical details that are easy to overlook:
Timing matters as much as product choice. Teagasc’s own seasonal guidance calls for nitrogen build-up through spring, with all areas of the farm typically targeted to receive 60 to 65 units of nitrogen per acre by mid-April. Protected urea is the recommended product across this build-up period, not just for a single early application.
Apply before rainfall where possible, not after a dry spell. Ammonia losses, whether from protected or untreated urea, are minimised when fertiliser is applied to moist soil or shortly before rain is expected, since moisture helps move the nitrogen into the soil profile quickly. Applying onto dry soil ahead of a dry period increases the window during which nitrogen can be lost as ammonia, regardless of which product is used.
Incorporation or injection reduces losses further. Where field conditions and equipment allow, incorporating fertiliser into the soil rather than leaving it on the surface reduces ammonia losses from any urea-based product, protected or not.
Coordinate timing with slurry and lime applications. Teagasc guidance includes specific timing-lag advice between lime, urea, CAN, and slurry applications, since applying these too close together can reduce the effectiveness of each. A well-sequenced nutrient management plan gets more value from protected urea than treating it as an isolated decision.
Financial support is available for the wider nitrogen efficiency picture. Ireland’s TAMS III grant scheme supports a range of related on-farm investments, including Low Emission Slurry Spreading equipment, at up to 60% grant aid, which connects directly to getting more value from the nitrogen you do apply, since better application method matters alongside better product choice.
The strong evidence: nitrous oxide
On nitrous oxide specifically, the case for protected urea is well established. Research conducted across grassland sites in Ireland found that amending urea with NBPT reduced the direct nitrous oxide emission factor to an average of around 0.40%, compared with roughly 1.49% for calcium ammonium nitrate (CAN), a commonly used alternative fertiliser. A separate widely cited study found that switching from CAN to NBPT-treated urea reduced nitrous oxide emissions by as much as 73% per kilogram of nitrogen applied. That’s a substantial, well-documented reduction, and it’s the core reason protected urea has been so heavily promoted.
The part that gets left out: ammonia versus CAN
Here’s where the story gets more complicated, and where a lot of simplified advice falls short. Protected urea’s job is to reduce ammonia losses compared with untreated urea. It does that reliably. But when protected urea is used to replace CAN specifically, rather than untreated urea, research has found it can actually lead to higher ammonia emissions than CAN, even though its nitrous oxide performance remains better.
This matters because a lot of Irish farms are switching directly from CAN to protected urea, not from untreated urea. If your farm made that specific switch, you likely improved your nitrous oxide number while potentially seeing an increase, not a decrease, in ammonia losses. Neither outcome is a failure. It’s simply a trade-off that’s rarely explained clearly, and one worth understanding if you’re trying to give an honest account of what your farm’s nitrogen strategy has actually achieved.
Why it’s hitting its ceiling
Protected urea was always a substitution strategy: swap one fertiliser type for a better-performing one, using the same basic amount of nitrogen. That’s a useful first step, and it explains why adoption happened so quickly, it required no change to farm system, herd size, or grazing pattern. Some of the most advanced farms in Ireland’s own Signpost sustainability programme are now targeting 100% protected urea use as a matter of course, which tells you how thoroughly this first step has already been absorbed across the leading edge of the sector.
But a substitution strategy has a natural ceiling. Once most of the farms in a region have already made the switch, the next unit of improvement doesn’t come from swapping fertiliser type again. It comes from reducing how much nitrogen is applied in the first place, improving how efficiently that nitrogen is used by the herd and the land, or combining fertiliser strategy with complementary approaches like increased clover content in swards, which fixes nitrogen biologically and reduces the need for synthetic input altogether.
What a realistic next step actually looks like
- Know which fertiliser you’re actually replacing. If you’re moving from CAN to protected urea, track ammonia as well as nitrous oxide, since the trade-off described above may apply directly to your farm.
- Treat nitrogen use efficiency as the next metric to improve, not just fertiliser type. This means asking how much of the nitrogen applied is actually taken up by the grass and converted to milk, rather than how “clean” the fertiliser itself is.
- Look at clover incorporation as a complementary strategy, not a replacement. Biologically fixed nitrogen from clover reduces the total synthetic nitrogen requirement, which addresses the ceiling protected urea alone cannot.
- Apply best practice regardless of fertiliser type, including timing around rainfall, incorporation where feasible, and coordinating with lime and slurry applications rather than treating each nutrient decision in isolation.
- Check what grant support is available. TAMS III and related schemes support several of the practical investments (application equipment, storage) that make the rest of a nitrogen strategy work better.
How this fits inside a mitigation toolbox
A well-built mitigation toolbox treats protected urea as one option among several nitrogen-related strategies, not a standalone fix. Alongside a straight urea substitution, the same toolbox typically includes options like reducing manufactured nitrogen fertiliser directly, incorporating multispecies swards or clover to fix nitrogen biologically, and lower-emission fertiliser alternatives beyond urea itself. Modelling these side by side, rather than one at a time, is what actually reveals where a farm’s next real gain sits once the first substitution has been made.
Protected urea remains a sound choice for most Irish dairy farms, and the nitrous oxide evidence behind it is solid. The mistake is treating it as a finished strategy rather than a first step. The farms already asking “what’s next” have understood something the sector is only slowly catching up to: a single substitution, however well evidenced, was never going to carry the whole nitrogen strategy on its own.
Sources: Teagasc, “Protected Urea” (Mark Plunkett, Johnstown Castle); AHDB, “Use of protected urea to reduce emissions”; Harty et al. (2016), reducing nitrous oxide emissions by changing nitrogen fertiliser use from CAN to urea-based formulations; ScienceDirect, “Lowering the greenhouse gas and ammonia emissions from grassland-based dairy production”; Journal of Dairy Science, simulation of management practices to reduce nitrogen losses on well-drained grass-based dairy farms in derogation; Irish Farmers Monthly, “Management hints, April 2026”; Teagasc Signpost Programme, 2025 sustainability award finalists.
