Nitrogen fertiliser adjustment calculator for cereals and oilseeds

Based on RB209 fertiliser guidance, use this tool suggests potential changes to your typical farm nitrogen rates. Accounting for fertiliser and grain/oilseed prices, it calculates the adjustment in the amount of nitrogen to apply to cereals and/or oilseeds crops.

PLEASE NOTE: The nitrogen response equation in the calculator is currently being updated to accommodate N fertiliser prices above £1,300/t. Values above £1,300/t will currently return a invalid result.

Please be aware that the tool may not run on some old versions of Excel e.g. version 2007. If you have a older version please contact AHDB so that a member of staff can help put your figures in to the calculator.

An energy crisis contributed to unprecedentedly high fertiliser prices in 2021. This led to a new ‘economic optimum’ – or the point at which the value of extra grain produced is not worth the cost of the extra nitrogen applied (break-even-ratio) – for nutrient management.

To account for higher prices, we commissioned a review to extended RB209 fertiliser price tables:

• By up to £2.50 per kilogram of nitrogen (equivalent to £863 per tonne of ammonium nitrate)
• By up to £350 per tonne for cereals and £700 per tonne for rapeseed (to account for stronger prices)

The tool is based on the revised figures.

For a specified crop, this tool calculates*:

• Cost of nitrogen fertiliser (£/kg)
• Break-even-ratio (kgs of grain required to pay for a kg of nitrogen fertiliser)
• An estimated change to nitrogen application* (kg/ha)
• An estimate of the effect on yield/income (£/ha)
• An estimated impact on nitrogen fertiliser costs (£/ha)
• Total nitrogen fertiliser product required for the specified crop area planted (t)

*Compared to your typical/recommended nitrogen rate. Estimates provided can guide decision making. However, local adjustments may be required to fit specific circumstances.

Each crop calculation is based on six figures:

1. Crop type
2. Fertiliser product price (£/t)
3. Fertiliser product nitrogen content (%)
4. Expected grain price (£/t)
5. Typical/recommended nitrogen rate (kg/ha)
6. Crop area planted (ha)

When you click on ‘Download resource’ from the AHDB website and the calculator opens up in viewing mode only, at the top of the screen there should be a button that says ‘Download file’. Click on this and you should then be able to click on or open the downloaded file.

No. The calculator just works out the adjustment to apply to your nitrogen fertiliser rate. There are other apps and calculators available to calculate your recommended nitrogen application rate or use the RB209 publication. A link to RB209 can be found at the bottom of this page.

RB209 recommendations for nitrogen applications to wheat, barley and oilseed rape already take expected yield into account. Adjustments for fertiliser and grain/seed prices are additional to and separate from adjustments for expected yield, and they do not depend on expected yield, or on soil nitrogen supply or soil type. Current RB209 recommendations are set at Break-Even Ratios of 5 for cereals and 2.5 for oilseeds (kgs of grain/seed to pay for 1 kg of N fertiliser). 

As an example, the effect of increasing the Break-Even Ratio from 5:1 to 10:1  results in a similar reduction in optimum nitrogen rate for any cereal crop (wheat or barley) of about 50 kg N/ha and a similar reduction in yield of about 0.35 t/ha. It may seem surprising that crops yielding 8 and 12 t/ha have the same recommended change in nitrogen application rate and resulting change in yield. But this is because cereal and oilseed crops have a similar shaped nitrogen response curve near the economic optimum.

With the AHDB Nutrient management guide (RB209) acting as a foundation for discussions, our December 2021 webinar featured four expert perspectives: