Understand why nitrogen application is important

Do you follow the government’s fertiliser bible RB209 to the letter on every field?

For most growers, particularly those growing first wheats following either natural regeneration set aside or oilseed rape, the chances are the answer is probably “no”.

And “no” in all likelihood means applying at least 20% more nitrogen than RB209 advises, at least using the standard field assessment method.

That’s where the problems could start, says NFU policy director Andrew Clark.

“We’ve had at least 20 reports just to the NFU head office in the last six months of Environment Agency NVZ inspectors challenging farmers about nitrogen applications about not being compliant with RB209.

Reports to the regional offices are probably much higher.”

Non-compliance is no laughing matter – the implications for cross-compliance could result in growers’ single payments being docked.

And while the NFU has subsequently worked out an agreement with the Environment Agency leaving RB209 as the back-stop position (see FW News, 27 January) for NVZ and cross-compliance inspections, it still leaves growers needing to justify nitrogen inputs.

This year it will be important growers can demonstrate they knew why they needed to apply more nitrogen than RB209 recommended before the application, rather than searching for retrospective justification, TAG director Jim Orson says.

For growers, perhaps the easiest acceptable justification is to use a suitably qualified (eg FACTS qualified) adviser.

It could, however, open up a liability issue, NFU vice-president Peter Kendall notes.

“I’m not sure who would be liable if there were any problems.”

Advisers will need to think very carefully about the way they recommend nitrogen rates to farmers, agrees Mr Orson.

“If you’re exceeding RB209, write down why on the recommendation.”

Three situations are particularly likely to lead to RB209 recommendations being exceeded, according to Strutt & Parker agronomist Will Gemmill.

“The issue is most likely where growers have milling wheats – particularly new high yielding varieties – or first wheats after natural regeneration or first wheats after oilseed rape.”

The problems lie principally if growers calculate their soil nitrogen supply index using the field assessment method in RB209.

That uses three main pieces of information: Average rainfall, soil type and previous crop.

Most arable growers, particularly in East Anglia, but also in other parts of the country fall into either low or moderate average rainfall, meaning less nitrogen is assumed to have leached from the soil, and therefore less nitrogen needs to be applied.

On a deep clay soil in a low rainfall area, a situation not uncommon in East Anglia, it means the soil nitrogen supply index in RB209 is calculated to be either a four following oilseed rape or a five following rotational set-aside, Mr Gemmill says.

“According to RB209 it means a maximum of 100kgN/ha should be applied to wheat following oilseed rape, and 40-80kg following set-aside.”

Even in moderate rainfall areas the figures are only 150kgN/ha following oilseed rape and 100kgN/ha following set-aside, he says.

Similar amounts are recommended in low rainfall areas on medium soils.

“Data from other trials, and field experience, suggests you need 180-200kgN/ha for first wheats on clay soils,” Mr Gemmill argues.

“There is a bit of difference.”

TAG’s trials database casts doubts on the indexation in RB209 in a big way, Mr Orson says.

“We’ve got considerable concerns particularly after natural regeneration and oilseed rape, and in dry winters in East Anglia.”

The organisation is in discussion with the EA about how its 48-trial database of nitrogen response curves can be used to help farmers.

On milling wheats RB209 allows an extra 40kgN/ha to be applied above its baseline recommendation.

Yet growers of some of the newer milling wheat varieties, in particular, are finding they need to apply nearer 300kgN/ha to achieve both maximum yield and make protein quality.

“In 2004 I grew Xi19 as a second wheat,” says Mr Kendall.

“It yielded 3.9 t/acre after I gave it plenty of nitrogen – around 260kgN/ha – but it still failed to reach the 13% protein level for milling.”

One problem with RB209 is it doesn’t seem to take into account varietal differences, says TAG regional agronomist Christine Lilly.

That was highlighted in Kemira-sponsored trials across four varieties at three sites in 2005.

“In the Bainton trial Xi19 needed around 349kgN/ha, Malacca 263kgN/ha and Solstice 263kgN/ha to hit 13% protein.”

RB209 suggested 180kgN/ha would be sufficient for the medium-loam soil type following peas.

The EA will accept higher nitrogen rates on milling wheats, the Agency’s head of land quality Helen Wakeham says.

“But we do ask for extra evidence to justify it – yield targets, quality, past history.”