Coated urea fertilisers formulated to prevent nitrogen losses have shown no significant advantage over straight urea in independently conducted UK trials.

There has been an age-old debate over whether ammonium nitrate or urea is the most efficient and cost-effective source of nitrogen for arable crops.

Ammonium nitrate is considered to be the best option by some due to its instant availability to the plant and being less prone to losses from volatilisation, particularly in dry conditions.

It is also better for milling wheat growers, with urea more likely to depress grain protein and could result in milling specification not being reached.

However, urea fertilisers contain a higher proportion of nitrogen, which can reduce the bulk required on farm, easing logistics and storage requirements.

NIAB TAG’s Ben Freer said it can also be applied in one high dose early in crop development and suffer no yield penalty, removing the necessity for multiple passes.

“It has historically been cheaper per unit of N compared with ammonium nitrate too,” said Mr Freer.

The introduction of so-called nitrogen “stabilisers” was boasted to bring the performance of urea fertilisers in line with that of ammonium nitrate.

The products are claimed to slow down the volatiliastion process, keeping more nitrogen in the root zone for uptake by the crop after application, boosting crop growth.

Stablisers are therefore bringing the performance of urea fertilisers – which can lose up to 50% of its nitrogen applied – in line with that of ammonium nitrate.

Speaking at the Association of Independent Crop Consultants (AICC) conference, Mr Freer explained there was no evidence that using coated urea provided a yield benefit for growers wishing to take advantage of the cheapest form of nitrogen fertiliser.

“The work we have undertaken shows that if you are thinking of switching to urea fertiliser, you don’t need the coating to get the advantages that urea can provide,” he explained.

Most of the previous research using these products had been carried out in the US, where urea represents the majority of the fertiliser market.

“The data from the US when using nitrogen stabilisers shows some more positive results, but you have to question whether that data is relevant here the UK.

“The manufacturers were basing their claims on that data and looking at our work, it seems like those claims may not be justified,” said Mr Freer.

In seven different trials since 2011 he explained there had been no evidence of a significant yield response from using coated granular urea products across a range of soil types.

Coated granular urea, containing additives such as Koch’s Agrotain and Carrs Billington’s Nutrisphere-N showed positive yield responses in some situations.

However, this was countered by observations of straight urea providing the highest yield response, resulting in no significant trend either way.

Mr Freer pointed out that the UK data set remains relatively limited and not all variations of enhanced urea, untreated urea and ammonium nitrate have been compared within the same trial.

“It would be good to get all these products side by side in the future to investigate their differences with the same doses and application timings,” he added.

More on this topic: Trials will fine tune nitrogen needs for wheat