How special urea outperforms ammonium nitrate fertilisers

Crops treated with a special urea are using nitrogen more efficiently, according to trials by farm management company Velcourt and fertiliser supplier Cofco International.

BASF’s Limus-protected urea includes a urease inhibitor that improves nitrogen use efficiency  by reducing nitrogen losses from volatilisation – helping to ensure more nitrogen is readily available to the crop.

The trials suggest that applications of Limus-protected urea significantly improve nitrogen recovery and overall nitrogen use efficiency compared to applications of ordinary ammonium nitrate (AN).

As well as a substantial cost benefit over AN, the results show Limus-protected urea is by far the most effective means of getting vital nitrogen into crops this spring, says Cofco International UK fertiliser manager Russell Davison.

“It’s a very challenging time for UK growers at the moment, not just because of the rise in fertiliser prices generally but also because of the shortage of AN and AN-based products in the market, be they imported or produced domestically.

Mid-February prices were sitting at around  £560/t for AN and £540/t for straight urea. But the price differential is even greater because AN contains 33.5-34.5% nitrogen and urea is 46% nitrogen.

“The challenge with urea is managing potential loss of nitrogen to the atmosphere particularly when applications are in unfavourable conditions.

“This is highlighted by the Clean Air Strategy which will limit the times at which uninhibited urea can be used to between Jan 15th and March with these measures set out to reduce the negative effects of ammonia pollution on the environment and human health.

Dual-action

Protected ureas offer a viable alternative to AN with the addition of a urease inhibitor, says Mr Davison. It helps limit release of gaseous ammonia so more nitrogen is available to crops. But not all such products are the same.

“BASF Limus is an innovative ‘dual-active’ product in that it contains two specific urease inhibitors – enabling it to reduce ammonia emissions more effectively than products containing a single inhibitor.”

Emissions can be reduced by up to 98% over straight urea, adds Mr Davison.

“The treatment adds around £40-£50/t to the cost of the urea but the benefits are immense. Adding this to the £560/t cost of urea makes it £600-610/t which is still significantly lower than AN on a cost of nitrogen basis.

“ When you take into account the higher N% of urea, the AN would have to be priced at £450/t, over £100 less than where it currently sits, to make it an economically attractive alternative to the treated urea.”

Nick Anderson, head of crop technology at Velcourt, says the big question is whether Limus is as effective as AN at getting nitrogen into crops – and that is where the trials are shedding some interesting light.

“It’s fair to say the standard approach to describing inhibited ureas in the past has been that they probably allow urea to perform as well as AN in the field, but our results from 2022 showed Limus-treated urea performing slightly better than AN.

“Aggregated results from two sites – one with heavy moisture retentive soil and the other on lighter droughty land near Stamford, in Lincolnshire – show Limus-treated urea delivers an average 3.4% increase in nitrogen recovery compared to AN in winter wheat.

“These take into account both improvements in yield and protein content of the grain.  Statistical analysis allows us to say with more than 99% confidence that the crops recovered more Nitrogen where this was applied as Limus-treated urea.

“Another way of looking at it would be to say the Limus-treated urea improved nitrogen use efficiency  by 3.4% compared to AN. This is highly significant when fertiliser is expensive and getting the most out of every application is critical.

“I think we can say with confidence, therefore, that Limus-treated urea will perform on average at least as well as AN and in some cases it will be better. There were clear advantages on both light and heavy soils.”

Cost benefits

The nitrogen recovery seen in the Velcourt trials is similar to that seen in BASF’s own worldwide trials programme, which further validates the findings, adds Mr Anderson.

“I think there’s growing confidence that the sort of advantages we are seeing for Limus are credible and consistent and there’s a real opportunity for growers to take advantage of this.

“In terms of break-even ratios, I would say you are looking at 7:1 for most people with AN now and around 5:1 for Limus-treated urea, which is a really significant difference and represents a sizeable cost benefit for Limus over AN.

“Plus, of course, it is widely reported that the carbon footprint of urea as an N source is much lower than that of AN, particularly imported AN. So however you look at it, there are now very strong arguments for switching out of AN to this type of treated urea.”

All prices in this article are correct at the time of writing)