Protected urea vs urea: when is a urease inhibitor worth it?

What 'protected' urea means

GRDC calls these products enhanced efficiency fertilisers (EEFs). There are three kinds you will see on urea:

• Urease inhibitor (NBPT). Slows the breakdown of urea at the granule, so less nitrogen turns into ammonia gas and is lost to the air (volatilisation). GRDC says NBPT is currently the only urease inhibitor compound sold commercially. Examples: Green Urea NV, Urea N-Shield NBPT and Agfert N-Shield NBPT.
• Nitrification inhibitor (such as DMPP or DMP-G). Keeps nitrogen in the ammonium form for longer, so less is lost by washing below the roots (leaching) or to waterlogged soil (denitrification). Incitec Pivot's eNpower coating is one example.
• Dual inhibitor. Both of the above. GRDC notes there are few on the market and limited research on how well they work. Examples: Urea N-Shield Dual and Agfert N-Shield Dual Urea.

Check the label: the nitrogen content is the same as plain urea (about 46% N), so you are paying for the coating, not extra nitrogen. Compare Granular Urea and Green Urea NV side by side.

How much nitrogen does plain urea lose?

It varies a lot with soil and weather. A worldwide review puts the average at about 16% of the nitrogen applied, rising to 40% or more in hot, humid conditions. CSBP's WA paper cites losses of up to 30% in WA field trials, and says losses can be high two to six days after spreading if there is not enough rain to wash the urea in. Australian measurements by soil type are in how much N urea loses.

GRDC (University of Melbourne) says loss is greatest when urea is spread on the surface of soils high in organic matter, in dry, warm, windy weather (often autumn and spring). Pastures, heavy stubble and high organic matter soils lose more.

When a urease inhibitor is worth it

• Surface spreading with no reliable rain forecast. The worldwide review says inhibitors work best when rain, irrigation or incorporation comes within about 5–7 days of spreading, while the inhibitor is still active.
• Spreading ahead of rain to fit your logistics. Incitec Pivot says Green Urea NV gives up to 14 days of flexibility ahead of rain (manufacturer claim).
• Pasture, heavy stubble and soils high in organic matter, where GRDC says losses are higher.
• Large areas where you cannot spread everything just before rain.

When plain urea is fine

• Rain or irrigation is guaranteed soon after spreading. GRDC says the urease inhibitor is not needed then, and CSBP found no benefit where there was enough rain shortly after spreading.
• You drill or band the urea below the surface. GRDC says deep placement largely eliminates ammonia loss.

What the trials show on yield

• Worldwide, a review found NBPT cut ammonia loss by about 53% on average, with an average yield gain of about 6% that varied by crop.
• Incitec Pivot's 2024 trials across SA, Victoria, southern NSW and Tasmania (wheat, barley, canola and pasture, 46 kg N/ha topdressed) found Green Urea NV cut losses by an average of 76–82% depending on the month. These are manufacturer trials and measured losses, not yield.
• CSBP's 2022–23 WA wheat trials of urea coated with NBPT and DMPP found an average 5.6% yield gain and 0.3% more protein over urea. The biggest gains were where conditions favoured losses. Where good rain fell soon after spreading, there was no benefit.
• GRDC says results are variable. Generally the inhibitor will not lift yield above what the recommended N rate achieves; the realistic gain is the same yield from less nitrogen when losses would otherwise be large.

So the decision comes down to the risk of losses on your paddock against the extra cost per tonne. Use the cost per kg of nitrogen guide and our nitrogen calculator with your own quotes, and browse all nitrogen products. If you are also weighing up other N forms, see urea vs ammonium sulphate and urea vs UAN. Always check with your agronomist before acting.