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What is a good CV for a fertiliser spreader?

The number at the top of every tray test report: what it means on the ground, the bands UK and Irish advisers use, and why the same spreader can have several.

By Spreadcheck, NSTS testers. Published . 6 minute read.

The short answer

Under 10% is very good, and up to 15% is acceptable in the field. Above 15%, AHDB says the spreader needs attention.

  • CV, the coefficient of variation, measures how much the rate varies across the bout, as a percentage of the average. Lower is more even.
  • AHDB’s RB209 says a CV above 15% means significant inaccuracies in spreading, and the spreader should be improved.1
  • Teagasc’s bands: under 10% excellent, 10–15% good, 15–20% poor, over 20% unacceptable.2
  • Tried & Tested: a well set up and operated spreader should give a CV of around 10% in a tray test.3
  • Stripes usually only show above about 20%, and yield is lost before you can see anything.4
  • A CV belongs to one fertiliser, one bout width and one set of settings. Change any of them and the CV changes.

What CV actually measures

On a tray test, trays are laid in a line across the full width of the spread, one every metre. The spreader drives past, each tray’s catch is weighed, and the pattern is overlapped at your bout width, the way it lands in the field when the next pass comes back the other way.

The CV is the standard deviation of those overlapped amounts divided by their average, as a percentage. In plain terms: it’s how far a typical strip of the field sits from the rate you set.

At a 200 kg/ha target, a 20% CV means some parts of the field are getting around 160 kg/ha and others around 240 kg/ha.5 That’s the same bag of fertiliser, spread on the same field, landing at very different rates a few metres apart.

8% CV

Trays across one 24 metre bout at an 8% CV: every tray close to the target line Tramline Mid-bout Tramline

At 200 kg/ha, every tray between about 177 and 223 kg/ha.

25% CV

Trays across one 24 metre bout at a 25% CV: well over the target near the tramlines, well under it mid-bout Tramline Mid-bout Tramline

At 200 kg/ha, trays from about 127 to 272 kg/ha.

Illustrative patterns across one 24 m bout, one tray a metre, after overlapping with the next pass. The dashed line is the rate you set. Both spreaders put on the same total.

Notice that both patterns put on exactly the same total. A rate check, where you weigh what comes out in a minute, would pass them both. Only a tray test across the full width tells them apart.

The bands UK and Irish advisers use

There’s no single legal pass mark for a fertiliser spreader. These are the lines the main advisers draw:

SourceWhat they say
AHDB, RB209 (UK, 2026)A well set-up spreader should achieve about 10%. Above 15% means significant inaccuracies; improve the spreader.1
Teagasc (Ireland)Under 10% excellent, 10–15% good, 15–20% poor, over 20% unacceptable.2
Farm Advisory Service (Scotland)Under 15% acceptable; 5% achievable after a professional test.6
Teagasc and the Fertilizer Association of IrelandUp to 15% acceptable in the field; above 20%, a crop and financial loss will result.7
NSTS (2015)Above 20%, striping becomes visible.4

You’ll often see 15% described as the standard. It’s the line RB209 and most advisers use, so it’s a fair benchmark, but treat it as the ceiling, not the target.

A test hall CV and a field CV are different numbers

Spreader manufacturers build their setting charts in test halls: level floors, no wind, a known sample of fertiliser. Kverneland says the widths in its charts are the widest that gave under 10% CV in its lab.8 Teagasc and the FAI note that test halls achieve under 5%, while up to 15% is acceptable in the field, and warn that test-hall figures in sales literature flatter machines.7

That gap is why a field test on your own farm, with your fertiliser, matters more than the figure in the brochure.

When can you see a bad CV?

Later than you’d like. NSTS put visible striping at above 20% CV, and pointed out that a crop without stripes is no guarantee of even spreading.4 Teagasc and the FAI say that above 20% a crop and financial loss will result.7

The money goes before the stripes appear. Independent consultant Ecopt put the cost in winter wheat at £8.79/ha at a 20% CV and £17.80/ha at 30%, at 2012 prices.9 Scotland’s Farm Advisory Service put a 25% CV, which it says is often found before testing, at about £20/ha in wheat and oilseed rape against the 5% a test can achieve.6

Losses rise faster than CV does. In New Zealand pasture trials, doubling the CV from 10% to 20% roughly quadrupled the lost growth.10 Our spreader test calculator uses AHDB’s nitrogen response curves and today’s prices: for feed wheat at 180 kg N/ha it puts the loss at about £19/ha at a 25% CV, against about £3/ha at 10%.11

The losses aren’t only yield. Over-fed strips bring a higher risk of lodging and disease, and can push malting barley over its grain nitrogen limit.112

One spreader, many CVs

A CV isn’t a property of the spreader. It belongs to a combination: this machine, this fertiliser, this bout width, these settings, this height and PTO speed. Change one and you have a different CV.

  • The fertiliser. In the 2011 Bygholm test hall trial, one spreader gave 13.6% on its chart settings and 5.1% after a tray test, with the same fertiliser. The chart was based on a coarser product than the batch tested.13
  • The width. Kverneland says not every fertiliser can be spread at every width.8 A product that spreads evenly at 24 m won’t necessarily do it at 36 m.
  • The set-up. Height, level, PTO speed and headland settings all move the pattern. The AIC advises a fresh tray test after servicing or new parts, and when headland equipment is used.14

That’s why an NSTS test adjusts the spreader for the best CV with each product,15 and why we include two fertilisers in every spreader test. Your report gives a CV and settings for each one.

How the CV on a test is measured

A CV is only as good as the trays behind it. With a tray every metre across the full spread, the overlapped pattern is measured at every point that matters, including the edges where the next bout takes over. With only a few trays, the gaps between them hide exactly the peaks and troughs that make up a poor CV.

On an SCS test we also analyse the fertiliser first, for bulk density, crush strength and granule size, so the settings on your report are tied to the product you actually tested.

Other questions people ask

What CV should a spreader get after a tray test?

With a decent fertiliser and a sound machine, under 10% is a realistic target. Scotland’s Farm Advisory Service gives 5% as achievable after a test,6 and in an independent test hall a tray test took one spreader from 13.6% to 5.1% on the same fertiliser.13 Expect a little worse in the field than on paper: wind, slopes and bumpy tramlines all add to it.

Does a low CV mean I’m putting on the right amount?

No. CV measures how evenly the fertiliser is spread, not how much. A spreader can be perfectly even at the wrong rate. That’s what a rate calibration checks, and RB209 asks for one every spring and every time the fertiliser changes.1 A full test checks both.

Why is my CV worse with urea?

Urea is lighter than most nitrogen fertilisers, about 0.75–0.8 kg a litre against about 1.0 kg for CAN, so it doesn’t throw as far and often needs a narrower bout or different settings.16 See spreading urea: how wide can you go?

Can I work out a CV myself?

Yes, if you have enough trays to cover the whole bout at one-metre spacing. Weigh each tray, overlap the pattern at your bout width, then divide the standard deviation by the average. A handful of trays can show whether the pattern is roughly right, but it can’t give you a reliable CV. See can you tray test your own spreader?

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. AHDB, Nutrient Management Guide (RB209), Section 1: Principles of nutrient management and fertiliser use, 2026.
  2. Teagasc, Fertiliser calibration, 2023.
  3. Tried & Tested, National Spreader Testing Scheme, accessed 2026.
  4. Farm Contractor & Large Scale Farmer, AEA to launch National Spreader Testing Scheme, 2015.
  5. Farmers Weekly, Adjust your tackle now for a spot-on spread, says IMATS, 1997.
  6. Farm Advisory Service (Scotland), Fertilisers and spreader calibration, 2018.
  7. Teagasc and the Fertilizer Association of Ireland, Precise Application of Fertiliser, Technical Bulletin 3, 2017.
  8. Kverneland, Kverneland spreading charts, accessed 2026.
  9. Farmers Weekly, Correct application makes the most of fertiliser (Ecopt figures), 2012.
  10. Journeaux, Massey University FLRC, Occasional Report 31 (economics of fertiliser spreading uniformity, citing Horrell et al. 1999), 2018.
  11. Spreadcheck, Spreader test calculator: method and sources, 2026.
  12. Maltsters’ Association of Great Britain, Barley requirements, accessed 2026.
  13. Farmers Weekly, Fertiliser spreader test: Amazone ZA-M, 2011.
  14. Agricultural Industries Confederation, Fertiliser Spreaders: choosing, maintaining and using, 2005, linked from RB209 2026.
  15. NSTS, Fertiliser spreader test, accessed 2026.
  16. Teagasc, Fertiliser spreader tray test and field procedure, leaflet 16, 2025.