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A clampdown on fertiliser emissions means more growers are considering switching to protected urea. Consider urea options carefully next season

A clampdown on fertiliser emissions means more growers are considering switching to protected urea.

Switching from straight urea to fertiliser featuring urease inhibitors can boost productivity while reducing emissions – but management must be tweaked, say experts.

Farmers have a key role to play in complying with the government’s increasingly stringent rules regarding urea-based fertiliser – not only to reduce ammonia emissions but to maintain market access to what is an important crop nutrient.

Defra’s clean air strategy requires growers who spread urea fertilisers to use so-called protected products from 1 April next year (see box). These products are treated with a urease inhibitor to reduce ammonia volatilisation after spreading by upwards of 70%.

It is important to comply with the new rule because an outright ban on  urea would be damaging, says Peter Scott (pictured right), technical director at Origin Fertilisers. Besides, he adds, urease inhibited urea can offer performance equivalent to ammonium nitrate (AN).

“Agriculture needs to maintain urea availability to offer alternatives for crop nutrition strategies. The industry has introduced efficient protected urea fertilisers to reduce environmental losses and make more of the fertiliser we are applying.”


For growers looking at protected urea for the first time, there are two distinct types of urease inhibitors that function in different ways. Farmers should ensure they purchase the most suitable product to make the most of the fertiliser they apply.

The most common type of inhibitor is phosphoric triamides. It is available in both solid and liquid forms as NBPT (Sustain), NPBT/ NPPT (Limus) and 2-NPT (Alzon Neo-N).

The other type of inhibitor is a carboxylic carbohydrate, with Nutrisphere being the sole option for UK growers. It is available in granular form from Origin Fertilisers as Origin Enhanced Nitrogen (OEN) and as a liquid from Agrii as Liqui-Safe.

Explaining the key differences between the inhibitors, Mr Scott says: “All phosphoric triamides use the same mode of action, forming an analogue of urease to block active sites, slowing urea hydrolysis, and reducing the risk of volatilisation.

“On the other hand, Nutrisphere is a combination of organic acids, which use a high cation exchange to temporarily sequester nickel in the soil, slowing down urea hydrolysis.”

Both offer similar performance to AN and there are fewer restrictions on the storage of urea-based fertilisers – and significant reductions in greenhouse gas emissions during production, says Mr Scott.

In addition, Nutrisphere is dual acting because it is also a nitrification inhibitor – helping to reduce the risk of nitrates leaching into water by sequestering the catalysts for nitrifying bacteria.

Combating degradation

One of the benefits of Nutrisphere is that it can be blended and stored with different nutrients – whereas phosphoric triamides have been proven to degrade when stored with phosphates, says Mr Scott.

This is due to the acidity of phosphate attacking the inhibitor and reducing its efficacy as a protected urea fertiliser. Consequently, this has restricted options for growers looking to use urea NP and NPK fertilisers.

Mr Scott explains how Nutrisphere differs in this case.

“Nutrisphere has EC certification – and part of the trial work involved testing its compatibility when blended with phosphate. It showed there is no weakening of the inhibitor in this situation, with the Nutrisphere still as effective at application.”