Farmers should understand the full picture when considering their Nitrogen source as Urea may look cheap but could well be expensive after volatilisation losses.

David Langton - Masstock’s crop nutrition specialist

It is important that farmers and their advisers remember the results from the large-scale independent NT26 research project completed in 2005 which concluded that Ammonium Nitrate is the best option for UK agriculture and the environment.

The Defra funded research was completed by a consortium of eminent researchers including ADAS, SAC, IGER and Rothamsted Research. They looked carefully at alternative Nitrogen sources for UK agriculture. The work was conducted over three seasons across 17 sites and included both grass and arable crops. For the first time the precise amount of ammonia lost to the atmosphere through volatilisation was actually measured. The results showed without doubt that using urea under UK conditions is a huge gamble. The accepted wisdom that applying urea early will prevent losses was proved to be completely unfounded.

“In cereals the losses ranged from 2% up to 43% of the total urea N applied,” explains David Langton Masstock’s crop nutrition specialist. “In grassland the losses were even more dramatic. There was a 58% loss of ammonia from urea applied to a clay grassland soil in Devon on 2 March and, at a nearby sandy soil site, 43% was lost from an even earlier application on 28 February.”

The research suggested that on average 20% more urea would be needed to maintain yields and quality but that is an average figure. “If you happened to apply when the conditions were just right then losses could be down to just 2%. In these circumstances you’d be over fertilising the crop so increasing the chances of lodging and yield loss and putting the environment at risk from leaching. On the other hand if you applied 20% more in a situation like those highlighted above where the loss of urea N turned out to be more like 40% or even 50% then the crop would be under fertiliser reducing yield and quality,” he says.

The biggest challenge of using urea under UK conditions is that it is simply not as reliable as ammonium nitrate. In short choosing urea is a much riskier option.

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