How often should a fertiliser spreader be tested?
What the law says, what Red Tractor asks for, and what AHDB and the fertiliser industry advise, side by side, with the wording checked against the source.
The short answer
Tray test the spread pattern at least once a year, before the main season, and check the rate every time you change fertiliser. That’s AHDB’s advice, and it more than covers Red Tractor’s annual calibration.
- No UK law requires a spreader used only for fertiliser to be tested. In NVZs and in Wales, the law does require nitrogen to be spread as accurately as possible.12
- Red Tractor requires all fertiliser application equipment to be maintained and calibrated at least once a year, with a record.3
- AHDB’s RB209: calibrate for rate every spring and whenever the fertiliser type changes, and check the spread pattern with trays, ideally every year.4
- The Agricultural Industries Confederation goes further: a tray test for every new type, brand or batch, after servicing, and when you use headland equipment.5
- Slug pellets change the rules. Under the Sustainable Use regulations (the SUD), slug pellet applicators must be NSTS tested before they’re five years old, then at least every six years, and Red Tractor and SQC apply that to a fertiliser spreader used for pellets.637
The rules side by side
People use “testing” and “calibration” for different things, so it helps to separate them. Calibration usually means checking the rate: how many kilograms a hectare are coming out. A tray test checks the spread pattern: whether those kilograms are landing evenly across the bout. A full NSTS spreader test does both.8
| Who | What they say | How often |
|---|---|---|
| The law: fertiliser | No testing duty. Spread nitrogen as accurately as possible in NVZs and in Wales; no manufactured fertiliser within 2 m of surface water.129 | None set |
| The law: slug pellets | Under the Sustainable Use regulations (the SUD), slug pellet applicators must pass an NSTS inspection.610 | By 5 years old, then every 6 |
| Red Tractor | All manufactured fertiliser application equipment maintained and calibrated, with a record (EC.10).3 | At least yearly |
| Scottish Quality Crops | Spreaders maintained, with an annual calibration on record; tested and calibrated for each product if used for slug pellets.7 | At least yearly |
| AHDB, RB209 | Calibrate for rate every spring and when the fertiliser type changes; check the pattern with catch trays.4 | Rate each change; trays yearly |
| AIC | Tray test for every new type, brand or batch, after servicing or new parts, and with headland equipment.5 | Every change |
| Thomas Bell | Calibrate the spreader separately for every type of fertiliser; always do a tray test.11 | Every change |
| Tried & Tested | Get every spreader tray tested before spreading starts in spring.12 | Every spring |
| NSTS (2015) | Test at least once a year to be sure you’re applying the recommended rate.13 | At least yearly |
So the floor is set by assurance, not law: a yearly calibration with a record. The advice from AHDB and the industry asks for more, because the thing that changes most often isn’t the spreader. It’s the fertiliser.
What Red Tractor actually asks for
Red Tractor’s Crops standard, EC.10, says all manufactured fertiliser application equipment must be maintained and calibrated at least annually, and you need a calibration record to show for it. The same wording appears in the Dairy and Beef & Lamb standards.31415 Scottish Quality Crops asks for the same yearly calibration, and its assessors may ask staff to show how they set up, calibrate and clean the spreader.7
Two things often get mixed up here:
- It doesn’t say tray test or NSTS. The standard asks for calibration. Red Tractor’s beef and lamb guidance accepts annual field calibration and records.15 A tray test is the way to check the spread pattern, which a rate calibration can’t.
- The per-product rule is for pesticides. You’ll read that Red Tractor requires calibration for every product. That rule applies to granular pesticide equipment, not to fertiliser spreaders.3
Slug pellets are the exception. Red Tractor’s EC.7 lists “slug pelleter (including electric spinning disc and hydraulic/PTO fertiliser spreaders)”: all need an NSTS test before they’re five years old, then every six years.3 SQC says a spreader used for slug pellets must be tested and calibrated for each product.7
When to test outside the yearly check
A yearly test sets the spreader up for the fertilisers you tested it with. These are the moments the advice says to check again:
- A different fertiliser. RB209 says to recalibrate the rate whenever the type changes.4 The AIC advises a tray test for each new type, brand or batch, and Yara, which makes fertiliser, says two batches of the same product can need different settings.516
- Work on the spreader. New vanes, discs or other parts, or a service. The AIC advises a fresh tray test after any of them.5
- Headland or border spreading kit. Also on the AIC’s list.5 Teagasc found headlands on 17 farms getting about 20% too little in the first 8 m and about 20% too much in the next 8 m.17
- A new tractor, or a new bout width. Working height, level and PTO speed all change the pattern.5 And not every fertiliser can be spread at every width.18
- Stripes, or a crop that looks uneven. RB209 says to check whenever faulty spreading is suspected.4 By then you’re usually already losing yield.
A full tray test for every delivery isn’t practical, and most advisers don’t ask for one. Teagasc’s approach is to check each batch for granule size, density and strength against the fertiliser the settings were made for, and only go back to the trays if it’s different.17 See how to check a delivery of fertiliser.
What farms actually do
Defra’s British Survey of Fertiliser Practice asks farms how often they check the spread pattern with catch trays. Among farms with a spreader, for crop year 2025:19
| How often | Share of farms |
|---|---|
| At each change of fertiliser | 6% |
| Once a year | 61% |
| Less than once a year | 17% |
| Never | 14% |
| “Factory set, doesn’t need checking” | 2% |
Most farms already check once a year. The gap is the change of fertiliser, which only one farm in seventeen checks, and which is when the advice says it matters most.
When to book
Test before your first pass of the season, with the fertiliser you’re actually going to spread. Most of our tests happen between January and May, so the diary fills up; book a few weeks ahead if you can. If you spread outside those months, we test all year round.
Bring the products you’ll use most. Every SCS spreader test includes two fertilisers, each with its own settings and CV on the report.
Other questions people ask
Is a fertiliser spreader test a legal requirement?
Not for a spreader used only for fertiliser. The legal duty is about the result: in NVZs and in Wales, nitrogen must be spread as accurately as possible, and manufactured fertiliser must not land within 2 m of surface water.129 Slug pellets are different: pellet applicators must be tested by law, under the Sustainable Use regulations (the SUD),6 and Red Tractor and SQC count a fertiliser spreader used for pellets as a pellet applicator.37 See do slug pellet applicators need testing?
Does Red Tractor require an NSTS spreader test?
No. Standard EC.10 asks for fertiliser application equipment to be maintained and calibrated at least annually, with a calibration record. It doesn’t name a tray test or an NSTS test.3 Red Tractor’s beef and lamb guidance says annual field calibration and records are acceptable.15 An NSTS test report is a dated record of the machine check, the rate and the spread pattern, so it covers the requirement and more.
Do I need to recalibrate for every fertiliser?
For the rate, yes: RB209 says to calibrate whenever the fertiliser type changes,4 because different products flow through the spreader at different speeds. For the spread pattern, RB209 asks for a tray check every year; the AIC and Yara advise one for each product.520 A sensible middle course is a full test each year with your main products, and a quick check whenever a delivery looks different.
How often does a sprayer need an NSTS test?
The rules for sprayers are separate. By law, a boom sprayer over 3 m needs its first test before it’s five years old, then at least every three years.21 Red Tractor’s Crops and Fresh Produce schemes and SQC go further and require an annual NSTS test for booms over 3 m; Red Tractor Beef & Lamb and QMS ask for every 3 years.3722
Does a new spreader need testing?
Yes. A new spreader comes with the manufacturer’s settings, but not with your tractor, your fertiliser or your fields. Our full guide to testing a new spreader sets out the evidence.
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
- gov.uk, Using nitrogen fertilisers in nitrate vulnerable zones, 2024.
- legislation.gov.uk, The Water Resources (Control of Agricultural Pollution) (Wales) Regulations 2021, Part 4, 2021.
- Red Tractor, Combinable Crops and Sugar Beet Standards, version 5.1, EC.7 and EC.10, February 2025.
- AHDB, Nutrient Management Guide (RB209), Section 1: Principles of nutrient management and fertiliser use, 2026.
- Agricultural Industries Confederation, Fertiliser Spreaders: choosing, maintaining and using, 2005, linked from RB209 2026.
- legislation.gov.uk, The Plant Protection Products (Sustainable Use) Regulations 2012 (the UK’s “SUD” rules), regulation 12, 2012.
- Scottish Quality Crops, The SQC Standards, 1.11, 2.17 to 2.19, October 2026.
- NSTS, Fertiliser spreader test, accessed 2026.
- gov.uk, Rules for farmers and land managers to prevent water pollution, 2026.
- NSTS, Slug pellet applicator test, accessed 2026.
- Thomas Bell, Fertiliser spreader settings, accessed 2026.
- Tried & Tested, National Spreader Testing Scheme, accessed 2026.
- Farm Contractor & Large Scale Farmer, AEA to launch National Spreader Testing Scheme, 2015.
- Red Tractor, Dairy Standards, EC.10, 2025.
- Red Tractor, Beef and Lamb Standards, EC.10 and guidance, 2025.
- Yara UK, Spreading preparation, accessed 2026.
- Teagasc (Dermot Forristal), Accurate spreading: six steps you need to take, Today’s Farm, 2023.
- Kverneland, Kverneland spreading charts, accessed 2026.
- Defra and Scottish Government, British Survey of Fertiliser Practice: fertiliser use on farm crops for crop year 2025, Section C1, 2026.
- Yara UK, Spreader calibration, accessed 2026.
- legislation.gov.uk, The Plant Protection Products (Sustainable Use) Regulations 2012, regulation 11 (boom sprayers over 3 m), 2012, as amended.
- Red Tractor, Fresh Produce Standards, version 5.1, EC.7, February 2025.