Every season agronomists face the same question: ammonium nitrate or urea? Both supply nitrogen; both are used on all cereals, oilseeds, and industrial crops. But each has its own strengths, limitations, and economic logic. Let's break it down.
Composition and Nitrogen Content
Ammonium nitrate (NH₄NO₃) per GOST 2081-2010 contains 34.4% nitrogen. Its key feature is that nitrogen is present simultaneously in two forms: nitrate (NO₃⁻, 17.2%) and ammonium (NH₄⁺, 17.2%). Nitrate nitrogen is taken up by plants immediately; ammonium nitrogen is absorbed gradually as nitrification proceeds in the soil.
Urea (CO(NH₂)₂) contains 46.2% nitrogen in amide form — the highest of all solid nitrogen fertilizers. In soil, the amide form first hydrolyses to ammonium with the help of urease, then nitrifies. The process takes 3–7 days depending on soil temperature and moisture.
Key Difference: Speed of Action
Ammonium nitrate starts working with the first rainfall or irrigation — nitrate nitrogen enters the soil solution immediately. Urea requires 3–7 days for hydrolysis. In cold weather (+5…+8°C) hydrolysis slows down, making early-spring top-dressings more effective with ammonium nitrate.
Urea, however, is more effective for foliar feeding and in soils with leaching conditions, where nitrates are washed into deeper horizons.
Comparison Table: Ammonium Nitrate vs Urea
| Parameter | Ammonium Nitrate | Urea |
|---|---|---|
| Nitrogen content | 34.4% (GOST 2081-2010) | 46.2% (GOST 2081-2010) |
| Nitrogen forms | Nitrate + ammonium | Amide (requires hydrolysis) |
| Speed of action | Fast (immediate) | Moderate (3–7 days) |
| Effectiveness in cold soil (<8°C) | Effective | Slow |
| Foliar feeding | Limited (burns >3%) | Excellent (10–15% solution) |
| Explosion hazard | Hazard class IV | Non-explosive |
| Storage requirements | Separate warehouse, special conditions | Standard dry warehouse |
| Hygroscopicity | High | Moderate |
| Quantity per 1 kg N | 2.91 kg | 2.16 kg |
| Nitrogen leaching risk | High (nitrates) | Lower (NH₄⁺ is adsorbed) |
Economics: Cost per Unit of Nitrogen
The correct way to compare fertilizers is not by price per tonne, but by cost per 1 kg of active ingredient (nitrogen). Example calculation:
Suppose ammonium nitrate costs $180/t and urea costs $220/t. Then:
- Cost per kg N in ammonium nitrate: 180 ÷ 344 = $0.52/kg N
- Cost per kg N in urea: 220 ÷ 462 = $0.48/kg N
Urea turns out ~9% cheaper per unit of nitrogen. At volumes of 100+ tonnes, this represents significant savings per season. Don't forget to factor in storage losses (both are hygroscopic), transport costs (less urea needed by weight), and leaching losses on light soils.
Application Rates: Converting Between Fertilizers
If a nutrient management plan was written for one fertilizer and you want to use the other, convert using the formula:
Rate Conversion Formula
Urea dose = Ammonium nitrate dose × (34.4 ÷ 46.2) = Ammonium nitrate dose × 0.745
Ammonium nitrate dose = Urea dose × (46.2 ÷ 34.4) = Urea dose × 1.343
Example: ammonium nitrate rate 200 kg/ha → urea needed = 200 × 0.745 = 149 kg/ha
When to Choose Ammonium Nitrate
Ammonium nitrate is preferred in the following situations:
- Early-spring top-dressing of winter crops when soil temperature is below +8°C — nitrate nitrogen works immediately
- Soils with neutral or alkaline reaction (pH 6.5–8.0) — lower ammonia volatilisation losses compared to urea
- Crops with a short growing season requiring a fast start
- Irrigated farming — nitrate nitrogen distributes evenly with irrigation water
- Farms already equipped with certified ammonium nitrate storage
When to Choose Urea
Urea has advantages in the following cases:
- Foliar top-dressing — a 10–15% solution does not cause leaf scorch
- Light sandy soils with leaching regime — ammonium nitrogen is less mobile than nitrate
- Base application in autumn or early spring under warm conditions
- Tank mixing with pesticides (after compatibility check)
- Farms without the ability to meet special nitrate storage requirements
- Early spring top-dressing (below +8°C)
- Irrigated farming
- Soils with pH above 6.5
- Cereals requiring a fast start
- No conditions for foliar application
- Foliar top-dressing
- Light soils with nitrate leaching
- Tank mixes with pesticides
- No licensed nitrate storage available
- Large volumes — transport savings
Combined Use: Can They Be Mixed?
Ammonium nitrate and urea should not be blended dry — the mixture absorbs moisture quickly, cakes, and loses flowability. However, both are components of liquid UAN (urea-ammonium nitrate solution), where they are dissolved together. UAN combines the advantages of both: fast action of nitrate nitrogen and prolonged effect of ammonium and amide nitrogen.
If a farm uses both fertilizers, the optimal strategy is ammonium nitrate for spring root top-dressings and urea for foliar applications in tank mixes.
Documentation and Standards
AgroChemProm supplies ammonium nitrate and urea with a full documentation package: GOST 2081-2010 conformity certificate, EEU TR declaration, and a quality passport with laboratory analysis results. Documents are accepted for agricultural subsidy applications.