When choosing a liquid fertilizer, the key question is which nutrients the crop needs. UAN and UAN + S offer different answers: UAN contains 32% nitrogen, while UAN + S combines 28% nitrogen and 5% sulphur. This difference also changes the quantity of product needed for the planned nutrition programme.
What do the two products contain?
Both fertilizers contain nitrogen in three forms — amide, ammonium and nitrate. Their proportions, however, differ:
| Parameter | UAN | UAN + S |
|---|---|---|
| Total nitrogen — N | 32% | 28% |
| Amide nitrogen | 16% | 12.8% |
| Ammonium nitrogen | 8% | 8.8% |
| Nitrate nitrogen | 8% | 6.4% |
| Sulphur — S | Not declared | 5% |
The figures are nominal percentages by mass. Full specifications and permitted tolerances are available on the product pages for UAN and UAN + S.
How does this affect quantities?
One tonne of UAN supplies 320 kg of nitrogen. One tonne of UAN + S supplies 280 kg of nitrogen and 50 kg of sulphur.
If we compare the products at the same nitrogen quantity — for example, 320 kg N — the calculation is:
- 1,000 kg of UAN supplies 320 kg N.
- Approximately 1,143 kg of UAN + S supplies the same 320 kg N, together with approximately 57 kg S.
Replacing one product with the other tonne for tonne therefore changes the nutrient supply. When switching to UAN + S, the quantity is recalculated for both nitrogen and sulphur.
What is the role of ATS in UAN + S?
UAN + S combines urea, ammonium nitrate and ammonium thiosulphate — ATS. The product specification describes the inhibitory effect of ATS on nitrification and its role in retaining nitrogen in ammonium form for longer. The duration of this effect depends on soil conditions.
How do we choose in practice?
UAN is an option when planning nitrogen nutrition. UAN + S is an option when the programme includes both nitrogen and sulphur.
Both products can be used before sowing and for top dressing. The specific rate, timing and application method depend on the crop, growth stage and conditions. When applying them together with crop protection products, the compatibility of the specific combination must be checked.
Planning your next fertilizer application? Explore the specifications for UAN and UAN + S or contact Agroexperts, so we can discuss selection and delivery for your farm.