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How to calibrate a fertiliser spreader

Calibration makes sure the right amount comes out. Here’s the sum, a calculator to do it for you, and the check itself, step by step.

By Spreadcheck, NSTS testers. Published . 4 minute read.

The short answer

Work out the flow you need, kilograms a minute = kg/ha × bout width in metres × forward speed in km/h ÷ 600, then catch what the spreader actually puts out over a timed run and adjust until the two match. Do it every spring and every time the fertiliser changes.

  • At 200 kg/ha, a 24 m bout and 12 km/h, the spreader needs to put out 96 kg a minute.1
  • Check your forward speed first: time 100 m from a rolling start; km/h = 360 ÷ seconds.2
  • Use your manufacturer’s calibration procedure. Teagasc’s simple version: take off one disc, collect for 30 seconds, and multiply by 4 to get kilograms a minute.2
  • RB209 says to calibrate for rate every spring and whenever the fertiliser type changes.3
  • Calibration gives you the right amount, not an even spread. Only a tray test across the full width shows where it lands.4

The sum

A spreader covers ground at your bout width times your forward speed. To put on the rate you want, it has to let out fertiliser at a matching flow:

kg a minute = rate (kg/ha) × bout width (m) × forward speed (km/h) ÷ 600

So at 200 kg/ha, on 24 m tramlines, at 12 km/h: 200 × 24 × 12 ÷ 600 = 96 kg a minute.1 Teagasc also has an online calculator that does the same sum.5

Work out your flow

Flow needed: 96.0 kg a minute. In Teagasc’s bucket check (one side, 30 seconds) you should catch 24.0 kg.

The rate check, step by step

  1. Check your forward speed. Mark out 100 m, set the engine for 540 rpm at the PTO, and time a run from a rolling start. Speed in km/h is 360 divided by the seconds taken.2 Don’t trust the dashboard: tyre size changes the reading.6
  2. Work out the flow you need with the sum above.
  3. Set the spreader from the chart for your fertiliser, rate, width and speed. See where to find your chart.
  4. Catch what comes out. Follow your spreader’s own calibration procedure: many have a chute or kit for it, and some need a disc or the vanes taken off.6 Teagasc’s simple version is to remove one disc, run the agitator, open the shutter for 30 seconds and catch the fertiliser in a bucket. Weight × 4 gives kilograms a minute from both sides.2
  5. Compare and adjust. If the catch doesn’t match the target, move the shutter setting and repeat. A longer catch gives a more precise answer.7
  6. Write it down. Product, batch, setting, catch and date. Red Tractor asks for a calibration record.8

An older method from Amazone catches from one side over a set distance instead of a set time: drive 41.6 m on a 12 m spreader and the catch × 40 gives kg/ha.9 By the same sum, drive 500 ÷ your bout width in metres; at 24 m, that’s 20.8 m.

What changes the rate

  • The fertiliser. Each product flows differently, which is why RB209 says to recalibrate whenever the type changes.3 Bulk density and granule size vary between batches, too.10
  • The weather. Flow changes with humidity, so a check from a dry day may not hold on a damp one.6
  • Quality in the shed. Rauch says to recalibrate when the fertiliser’s quality changes as well as when the product changes.7
  • Speed. Driving faster than you calibrated for puts on less, unless the spreader’s control adjusts for it.

What a rate check can’t tell you

A rate check tells you the total is right. It tells you nothing about where it lands. The AIC puts it bluntly: rate calibration gives only the correct amount.4 A spreader can put out exactly 96 kg a minute and still put half of it in the wrong strip.

That’s why RB209 asks for two separate checks: rate every spring and at every change of fertiliser, and the spread pattern with catch trays, ideally every year.3 See what is a good CV? and can you tray test your own spreader?

Other questions people ask

What is the calibration formula for a fertiliser spreader?

Flow in kg a minute = application rate in kg/ha × bout width in metres × forward speed in km/h ÷ 600.1 To go the other way: rate in kg/ha = kg a minute × 600 ÷ (bout width × speed). The 600 comes from converting metres and kilometres an hour into hectares a minute.

How often should I calibrate my spreader?

RB209 says every spring and whenever the fertiliser type changes.3 Rauch adds whenever the fertiliser’s quality changes, for example a damp or dusty batch.7 Red Tractor asks for calibration at least once a year, with a record.8

Does a spreader with weigh cells need calibrating?

Weighing spreaders calibrate the rate themselves as they go; Kverneland, for example, says its weighing Exacta TL needs no calibration test.11 But weigh cells measure how much comes out, not where it lands. Teagasc notes that even spreading isn’t necessarily helped by electronic control or GPS,12 so the spread pattern still needs a tray test.

Why does my application rate change from day to day?

Fertiliser flows faster or slower with humidity, granule shape and size,6 so a check from a dry morning may not hold on a damp afternoon. A new batch can flow differently too. If the rate looks wrong part way through a job, check it again rather than assume.

About this article

Written by Spreadcheck (Spreader & Sprayer Testing Ltd), an NSTS testing company at Rookery Farm, Wheaton Aston, Staffordshire, which wrote the original qualification for fertiliser spreader and slug pelleter testing that NSTS adopted. We sell testing, so every figure here links to its source, and we say where the evidence is mixed.

Checked on 12 October 2026. Rules, prices and guidance change, so follow the links for the latest.

Sources

  1. Teagasc, Fertiliser calibration sheet, 2025.
  2. Teagasc, Fertiliser spreader basic set-up and calibration, leaflet 15, 2025.
  3. AHDB, Nutrient Management Guide (RB209), Section 1: Principles of nutrient management and fertiliser use, 2026.
  4. Agricultural Industries Confederation, Fertiliser Spreaders: choosing, maintaining and using, 2005, linked from RB209 2026.
  5. Teagasc, Fertiliser calibration tool, accessed 2026.
  6. Teagasc and the Fertilizer Association of Ireland, Precise Application of Fertiliser, Technical Bulletin 3, 2017.
  7. Rauch, UKS operator’s manual, 2025.
  8. Red Tractor, Combinable Crops and Sugar Beet Standards, version 5.1, EC.7 and EC.10, February 2025.
  9. Amazone, ZA-U operator’s manual (German), calibration by distance, 1985.
  10. Yara UK, Spreading preparation, accessed 2026.
  11. Kverneland UK, Exacta TL weighing spreader, accessed 2026.
  12. Teagasc (Dermot Forristal), Accurate spreading: six steps you need to take, Today’s Farm, 2023.