How do you check fertiliser quality before spreading?

The bag tells you what’s in the fertiliser. It doesn’t tell you how it will spread. Three quick checks that do.

By Spreadcheck, NSTS testers. Published 12 October 2026. 7 minute read.

The short answer

Check three things against the fertiliser your spreader settings were made for: granule size with a sieve box, bulk density by weighing a measured volume, and hardness with a crush tester. If they’ve changed, so has your spread pattern.

A fertiliser’s chemical analysis is controlled. Its particle size, shape, strength and density aren’t, and they decide how it spreads and what setting it needs.¹
Teagasc’s targets: 80% of granules between 2 and 4 mm, and hardness above 6 on a hardness tester.² For urea, a crush strength above 5 kg, and never below 3 kg.³
Typical bulk density: urea 0.70–0.80 kg a litre, CAN 0.97–1.07 kg.⁴
Two batches of the same product can need different settings.⁵ Kverneland advises identifying fertiliser by granule size and specific weight, not by its name.⁶
Blend ingredients should be within about 10% of each other in size, or they separate.⁷

Why physical quality matters

A spinning disc throws every granule at roughly the same speed. How far each one flies depends on its size, its density, its shape and whether it survives the vane in one piece. Teagasc puts it simply: a fertiliser’s chemistry is controlled, but its particle size, shape, strength and density aren’t, and they have a big effect on spreading and on the right setting.¹

Size. Bigger granules fly further. In studies reviewed at Wageningen University, larger granular urea spread about 20 m where prilled urea spread about 10 m.⁸
Density. Lighter products slow down faster in the air. Teagasc says density has a large impact on spread width.²
Strength. Weak granules shatter on the vanes into fines, which land close to the tractor. In German spinning-disc tests, about 22% of a urea broke down into fines on the disc.⁸

And the faster the disc, the more these differences matter. In a published New Zealand model, a 1 mm and a 4.7 mm particle landed 7.3 m apart at the disc speeds needed for 30 m tramlines, but only 1.5 m apart at slower speeds.⁹ Wide bouts are less forgiving of a change in product.

Granule size

Check it with a sieve box or grader: shake a sample through stacked sieves and read off how much sits in each size band. Teagasc’s target is 80% of granules between 2 and 4 mm.²

On data sheets and in trials reports you’ll see size given as two numbers:

SGN, Size Guide Number. The median granule size in millimetres, times 100. An SGN of 300 means half the product by weight is above 3 mm.¹⁰
UI, Uniformity Index. How tight the size range is, comparing the small end with the large end. Ohio State’s extension service treats 40 to 60 as uniform.¹¹

A sieve box gives you a good guide, not a laboratory result. Granules sort themselves by size whenever fertiliser is poured into or out of a bag or heap,¹² so the fines end up at the bottom and a scoop off the top can look better than what will go through the spreader. Take samples from more than one place, mix them, and test the same way each time.

Watch the dust in the bottom of the box, too. Fines land near the tractor and pile up the middle of the pattern; in German work reviewed by Hofstee, CV rose as the share of fines rose.⁸

Bulk density

Fill a container of known volume, level it off without tapping, and weigh it. Kilograms divided by litres is the bulk density. Whichever way you do it, do it the same way every time, so this delivery compares fairly with the last. It matters twice: it changes how much flows through the spreader’s openings, so it changes your rate, and it changes how far the fertiliser is thrown.

Product	Typical loose bulk density, kg a litre
Urea, prilled or granular	0.72–0.82
Ammonium sulphate	0.79–1.04
Ammonium nitrate, high-density prills	0.85–0.98
DAP	0.88–1.10
MAP	0.90–1.10
TSP and muriate of potash	0.95–1.20

Figures from IFDC’s fertiliser testing manual, converted from kg/m³.¹⁰ NutriNorm gives 0.97–1.07 kg a litre for CAN.⁴ If your spreader has a rate controller that asks for bulk density, measure it for each product rather than using a book figure.¹¹

Hardness

A hand-held crush tester presses single granules until they break. Test a good number of granules and take the average.

Teagasc wants urea above 5 kg, and never below 3 kg.³
On farm testers in Ireland, good CAN usually reads 7–8 kg and good urea about 3 kg. Many farmers testing protected urea in 2024 got only 1–2 kg, and soft granules break on the vanes, travel less far and cause striping.¹³

One caution: there’s no agreed European standard for crushing strength, because laboratory trials couldn’t make different testers agree. Compare readings on the same tester, not with a figure from someone else’s.¹⁴

Blends

A blend is several products mixed together, and each ingredient has its own size, density and strength. If they don’t match, they separate: in the heap, in the hopper and in the air.

In the heap. In one Austrian trial, nitrogen in a heap of CAN mixed with potash ranged from 37.5% under target to about 21% over, depending on where the sample was taken.¹⁵
In the air. Amazone says blend ingredients with different properties land over different widths, and one setting that suits them all is usually impossible.¹⁶ Its setting chart covers the weight of fertiliser across the bout, not how each nutrient lands.¹⁷
On the tray. In New Zealand field tests, a blend that spread at an 11% CV by weight had its potash component spreading at about 35%.¹⁸ A good pattern on the scales can hide a poor one for each nutrient.

The Canadian Fertilizer Institute’s guide is that ingredients should be within about 10% of each other in size; more than 20% apart counts as incompatible. It also says not to blend ammonium nitrate with urea, because the mix takes on water even in a closed container.⁷

Storage

Quality can change after delivery. Damp makes granules soft and sticky, raises caking and dust, and can affect how the fertiliser spreads.¹⁹ Blends take on moisture at lower humidity than their ingredients do.²⁰ Yara UK advises stacking bags no more than three high, and says old stock may need different settings.⁵

Nobody has published how much a particular shed changes a particular batch. If a bag has been through a wet spring, check it again before you spread it.

What to do with the numbers

Record the batch you tested with. Granule size, bulk density and hardness, alongside the settings on your test report.
Check each new delivery the same way. This is Teagasc’s approach: characterise every batch and compare it with the fertiliser the settings were made for.¹
If it’s different, check the spread. A few trays across the bout will show whether the pattern has moved. A big change, or a product that isn’t in your spreader’s chart, needs a proper test. Amazone’s UK site asks for a 3 kg sample of unknown products for its own analysis service.²¹

On every SCS spreader test we measure the fertiliser’s bulk density, crush strength and granule size before the tray test, and we sell the grader box, strength tester and bulk density tester so you can check deliveries yourself. If you import, make or blend fertiliser, our independent spreading trials test your product on the UK’s most popular spreaders.

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

Teagasc (Dermot Forristal), Accurate spreading: six steps you need to take, Today’s Farm, 2023.
Teagasc, Fertiliser spreader tray test and field procedure, leaflet 16, 2025.
Teagasc, Key points for spreading protected urea, 2025.
NutriNorm (OCI Nitrogen), Quality of fertilisers, accessed 2026.
Yara UK, Spreading preparation, accessed 2026.
Kverneland, Kverneland spreading charts, accessed 2026.
Canadian Fertilizer Institute, Bulk Blend Quality Control Manual, 2013.
J. W. Hofstee, Wageningen University, Physical properties of fertilizer in relation to handling and spreading (PhD thesis), 1993.
Grafton et al., Massey University FLRC workshop, The ballistics of separation of fertiliser blends at wide bout widths, 2014.
IFDC, Manual for determining physical properties of fertilizer, 2016.
Ohio State University Extension, Physical properties of granular fertilizers and impact on spreading, FABE-550, 2025.
Miserque and Pirard, Chemometrics and Intelligent Laboratory Systems 74, Segregation of the bulk blend fertilizers, 2004.
Irish Farmers Journal, Is protected urea a runner in 2025?, 2025.
F. Samec, IFA Technical Conference, Physical properties of fertilizers and spreading: standardization, regulations and manufacture, 1996.
Moitzi et al., BOKU Vienna, CASEE conference, Segregation of solid fertilizer blending in a conical heap and due logistic activities, 2015.
Amazone UK, EasyMix press release, 2019.
Amazone, ZA-M fertiliser setting chart (Streutabelle), accessed 2026.
Holmes, Ekanayake, Nguyen and Werner, Massey University FLRC, The uniformity of ground spreading common New Zealand blended fertilisers, Occasional Report 36, 2024.
Yara, Physical properties of fertilizers, accessed 2026.
Fertilizers Europe, Guidance for compatibility of fertilizer blending materials, 2014.
Amazone UK, Conscientious fertiliser spreading, accessed 2026.
Rauch, notice of 16 February 2023, reproduced in an SKW Piesteritz presentation (LfULG field day, January 2024), slide 16, Vorsicht bei Harnstoffen mit Ureaseinhibitoren (caution with urea containing urease inhibitors), in German, 2023.