The practice of applying late nitrogen to boost grain proteins is coming under fire from some millers and food manufacturers. Louise Impey reports

If you’re planning to supply wheat on contract to Warburtons or Weetabix this year, there are strict rules regarding late nitrogen applications.

For Warburtons, no nitrogen can be used after GS39 (flag leaf), while Weetabix stipulates that applications can’t be made after GS47.

These conditions have been imposed because millers believe that late nitrogen doesn’t get into the grain as true protein. In other words, it improves grain nitrogen content, but not grain quality. Their preference is to see improvements in quality from soil applications of bagged fertiliser, rather than using a foliar application of urea at the milky ripe stage.

That goes against HGCA research and traditional farm practice, says Mark Tucker, head of agronomy at Yara . He is concerned that growers will find it difficult to meet the breadmaking specification of 13% protein without the use of urea. “The 13% target is about 1% more than you get in an optimally fertiliser crop,” he stresses.

“It’s particularly relevant for this season, as the dry spring conditions may have limited the amount of nitrogen that was taken up by crops,” he says. “Some 28% of milling wheat samples missed the quality target last year, and that could rise to closer to 40% this season.”

Crops that received last week’s rainfall will have taken up some nitrogen, admits Mr Tucker. “But many are low biomass crops, which tend to yield less. That means their protein contents are likely to be higher than usual and they will need checking.”

Mr Tucker says that past history is useful for telling a grower whether he needs to make changes to his nitrogen management. “Those who have had problems achieving 13% protein in the past should take steps to understand why.

“Others will already know that late nitrogen plays an important role on their farms.”

Extra nitrogen can be applied in two ways – either at the end of May at flag leaf emergence in granular form, or in July, at the milky ripe stage as a foliar spray of urea.

Both methods are effective, says TAG agronomist Neil Watson, but have different results. Applying up to 40kg/ha of bagged nitrogen at flag leaf will boost grain protein by 0.5%, providing there is sufficient soil moisture, while spraying the same amount of urea nitrogen in July raises proteins by nearly 1%.

“There’s no yield benefit from the July timing, while there’s a 0.1-0.2t/ha advantage from the flag leaf application,” he explains.

Those opting to use late urea should be aware that there’s a risk of scorch, especially on hot days, he warns. “Dull, overcast conditions are needed at spraying to prevent this occurring.”

Whichever method you choose – regardless of millers’ preferences – there are tools that can help growers target the right amount of nitrogen to their crops.

Yara’s N Tester, an in-field kit, gives an instant reading of the crop’s nitrogen status by measuring the chlorophyll content, and then helps to calculate how much extra nitrogen will be needed.

“The N tester requires 30 leaf samples to give a result,” says Mark Tucker. “The ideal is to have 4-4.5% nitrogen in the flag leaf at flowering. That’s an indication that you’re close to the optimal amount.”

Typically, an extra 40-60kg of nitrogen/ha is required for most breadmaking varieties, he reports. “If the grower isn’t allowed to apply this, because of the terms of his contract, there’s a considerable risk that the grain will be rejected.”

But Warburtons Group purchasing director Bob Beard points out that contracted farmers have consistently risen to the challenge of producing the wheat required. “And that’s even been the case in the more difficult harvest years.”

HGCA Research

HGCA-funded work conducted by Peter Dampney of ADAS shows that foliar urea is a more reliable method than solid ammonium nitrate when it comes to increasing grain protein content.

In his trials, the application of bagged ammonium nitrate at GS39 was not as effective as the use of foliar urea later on, probably because of delays in the movement of solid nitrogen into the soil and then into the crop.

“It’s a process that relies on soil moisture,” he points out. “And that isn’t always around at the end of May.”

He recorded a 0.66% rise in grain proteins with foliar urea and a 0.34% increase from bagged nitrogen. “Perhaps it’s the 13% grain protein target that needs reviewing, rather than fertiliser practice.”