Full explanation
'UAN' (without a number) is used colloquially by agronomists and in marketing materials when the specific grade doesn't matter. Official documents, specifications, and contracts always cite the full grade — UAN-28 (28% N, winter use due to lower crystallization temperature), UAN-30 (30% N, transitional grade), UAN-32 (32% N, main grade for spring season at ≥0°C). Crystallization temperatures: UAN-28 ≈ −17°C, UAN-30 ≈ −10°C, UAN-32 ≈ 0°C — so grade choice depends on storage conditions and season. Same producers: OSTCHEM, EU imports. Trade-off: UAN-32 is more expensive per kg of product but cheaper per kg of N; for small farms with seasonal use, UAN-28 may be more practical due to wider temperature range.