Nitrogen applications still worthwhile

Applying 250kg of bagged nitrogen per hectare can still be worthwhile where milling premiums are being sought, wheat breeder CPB Twyford says.

Group one wheats such as Malacca and certain group two varieties with ready-made added-value markets such as Cordiale and Solstice are worth pushing for 13% protein, CPB agonomist Lee Bennett says.

“While it is impotant not to over-use N on cost and environmental grounds, it is really important not to undercook crops, especially if you have signed up for high-protein contracts.”

Residual soil nitrogen levels and crop nitrogen contents are relatively high this season, Mr Bennett says. He recommends that unless the crop is backward, bagged nitrogen can wait until stem extension.

“You don’t want a thick, lush, leafy crop that encourages disease and lodging. Give it just enough at stem extension to build the canopy, in other words 200kgN/ha less the soil nitrogen contribution. In some fertile situations that may be as little as 60kgN/ha.”

Flag leaf applications should be the main target. “It is at this main dressing that you need to throw the book at the crop.”

On a variety such as Malacca, 13% protein at a 9.5t/ha yield will require 247kgN/ha to be available. Allowing for soil and plant inefficiencies, that means around 320kgN/ha is needed from residual soil supplies and the bag combined, Mr Bennett explains.

If the soil is providing around 80kgN/ha (not uncommon this season in first wheats after oilseed rape), that leaves a further 250kg of nitrogen to be applied.

At £80/ tonne for a group one wheat, a return of around £640/ha over nitrogen costs could be achieved even with ammonium nitrate at £170/tonne, he says.

Crop requirements need to allow for nitrogen already available in the leaves and nitrogen that will be mineralised in the soil. The Environment Agency has confirmed that under cross-compliance and Nitrate Vulnerable Zone rules, DEFRA’s RB209 fertiliser guidance document should be adhered to except where growers can demonstrate a justification for an alternative approach.

With a number of advisers suggesting RB209 does not cater adequately for the requirements of modern varieties, breeder advice and trials work can be a useful source of information to provide that justification, a number of experts have told Farmers Weekly Interactive

An investigation into soil sampling and nitrogen recommendations was carried out by Farmers Weekly Group out at the beginning of February. Reports appeared in Farmers Weekly 10 February and Crops 11 February.

Further coverage will appear in Crops 25 February issue.

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