Urea 46% Nitrogen: Specification Standards Every Agricultural Distributor Should Verify
Urea fertilizer's value proposition is simple: it is the highest-concentration solid nitrogen fertilizer available commercially, at 46% N by weight. This concentration is why it dominates global nitrogen fertilizer trade — it carries more plant-available nitrogen per ton shipped than any other solid fertilizer. But that 46% figure is a specification, not a guarantee. Understanding what else is in that ton, what the acceptable tolerances are, and how to verify quality before paying is the foundation of professional fertilizer procurement.
This guide provides the complete specification framework for urea 46% nitrogen — what each parameter means, what acceptable limits are, how to read a quality certificate, and what red flags to watch for in supplier documentation.
Why 46% Nitrogen Is the Standard — and Why Deviations Matter
The 46.0% nitrogen specification for urea is based on the molecular composition of pure urea:
- Urea molecular formula: CO(NH₂)₂
- Molecular weight: 60.06 g/mol
- Nitrogen content: 2 × 14.007 / 60.06 = 46.65% N (theoretical maximum for pure urea)
Commercial urea achieves 46.0–46.5% N after accounting for small amounts of biuret, moisture, and trace impurities. "46% N minimum" is the industry standard commercial specification.
Why deviations matter to distributors:
A 100 MT shipment of urea at 45.5% N instead of 46.0% N contains 500 kg less plant-available nitrogen than specified. At a retail nitrogen price of $1.20/kg N, this is $600 of nitrogen value missing from the shipment. Across 1,000 MT, the shortfall is $6,000 — and the distributor's downstream buyers will notice the performance deficit at crop level.
For government procurement programs (fertilizer subsidies, emergency food security programs) with nitrogen-content contracts, a 0.5% N shortfall can trigger contract penalties and reputational damage.
Complete Urea Specification Table
| Parameter | Standard Commercial Grade | High-Grade / Low-Biuret | Notes |
|---|---|---|---|
| Nitrogen content | Min 46.0% | Min 46.0% | Measured on dry weight basis |
| Biuret | Max 1.5% | Max 0.5% | Higher biuret = foliar phytotoxicity risk |
| Moisture | Max 0.5% | Max 0.3% | Affects nitrogen content calculation; increases caking |
| Free ammonia | Max 150 ppm | Max 50 ppm | Quality indicator; high NH₃ indicates degradation |
| Particle size (granular) | 90% in range 2–4 mm | 90% in range 2–4 mm | Uniformity matters for spreader performance |
| Particle size (prilled) | 90% in range 1–2.5 mm | 90% in range 1–2.5 mm | |
| Crush strength (granular) | Min 3 kg/particle | Min 4 kg/particle | |
| Anti-caking agent | Present (as per manufacturer) | Present | |
| Melting point | ~132–134°C | ~133–135°C | Low melting point indicates impurities |
| Color | White to off-white | White | Yellowing indicates excessive biuret/degradation |
| Oil content (if coated) | Max 200 ppm | Max 100 ppm | For anti-caking oil-coated grades |
| pH (10% solution) | 7.0–9.0 | 7.0–8.5 | High pH = high free ammonia |
The Biuret Parameter: Why It Matters More Than Most Distributors Realize
Biuret (H₂N-CO-NH-CO-NH₂) is a condensation byproduct formed when two urea molecules combine and release ammonia during synthesis:
2 CO(NH₂)₂ → H₂N-CO-NH-CO-NH₂ + NH₃
This reaction occurs primarily when urea melt is overheated or held at high temperature for too long in the manufacturing process. Modern urea plants with well-controlled synthesis reactors produce urea with biuret below 0.5%. Older or poorly controlled plants may produce biuret above 2%.
Biuret Phytotoxicity
Biuret is phytotoxic — it inhibits enzyme activity in plant cells, particularly at germination and early growth stages. The practical thresholds:
| Biuret Level | Application Risk |
|---|---|
| < 0.3% | Safe for all applications including foliar spray and sensitive crops |
| 0.3–1.0% | Safe for soil application; borderline for foliar spray |
| 1.0–1.5% | Acceptable for standard soil application to non-sensitive crops |
| > 1.5% | Risk of germination inhibition if banded near seeds; foliar phytotoxicity likely |
| > 2.0% | Significant phytotoxicity risk; avoid direct seed contact or foliar use |
For distributors supplying high-value horticultural crops (vegetables, fruits, tobacco), always specify and verify max 0.5% biuret. For standard broadacre crops (corn, wheat, rice, soy) via broadcast application, 1.5% maximum is adequate.
Testing Methods: How Nitrogen, Biuret, and Moisture Are Measured
Nitrogen Content Analysis
Standard method: Kjeldahl digestion (AOAC 955.04 or ISO 5315) or Dumas combustion method (ISO 13878).
- Kjeldahl: Sample is digested in sulfuric acid to convert all nitrogen to ammonium sulfate, then ammonium is distilled and titrated. Slower (2–4 hours); highly accurate.
- Dumas: Sample is combusted at 900°C+ under oxygen; all nitrogen is converted to N₂ gas and measured by thermal conductivity detector. Faster (5–10 minutes per sample); equally accurate.
Both methods report nitrogen as % N on the as-received basis. Dry weight basis calculation requires moisture correction.
Biuret Analysis
Standard method: Colorimetric method — biuret reacts with copper sulfate in alkaline solution to form a purple complex. Absorbance measured at 550 nm is proportional to biuret concentration. (AOAC 932.01, or ICUMSA-equivalent method for urea).
Rapid field test: Biuret test strips are available for qualitative screening — turn red in the presence of significant biuret. Not quantitative but useful for rapid rejection screening.
Moisture Analysis
Standard method: Karl Fischer titration or oven-drying (105°C, 4 hours). Karl Fischer is preferred for accuracy at low moisture levels (< 0.5%).
Reading a Urea Certificate of Analysis (COA)
A compliant COA for urea 46% N should contain:
- ☐Manufacturer name and plant location
- ☐Production lot/batch number
- ☐Production date
- ☐Product description: "Urea Fertilizer, Granular/Prilled, 46% N"
- ☐Nitrogen content (% N, dry weight basis)
- ☐Biuret content (%)
- ☐Moisture content (%)
- ☐Particle size distribution (mm range, % in range)
- ☐Crush strength (for granular — kg/particle)
- ☐Sampling date and sample identification
- ☐Testing laboratory name and accreditation reference
- ☐Laboratory technician signature and QC manager countersignature
- ☐Test method references (AOAC, ISO, etc.)
What should concern you:
- COA without laboratory accreditation reference — supplier may be self-testing without external validation
- Nitrogen content showing exactly 46.00% with no decimal variation — often indicates copy-paste from specification rather than actual test result
- Biuret exactly at specification limit (e.g., exactly 1.50%) — statistically suspicious; real test results vary
- Test results dated before production date — impossible; reject this document
SGS Inspection for Urea: What to Specify in the Scope
When commissioning pre-shipment SGS inspection for urea, specify:
Minimum scope:
- Weight survey (quantity verification)
- Nitrogen content (% N)
- Biuret (%)
- Moisture (%)
- Particle size distribution
- Color and visual appearance
Enhanced scope (for large orders or first transaction):
- Crush strength (granular)
- Free ammonia
- Bulk density
- Anti-caking agent confirmation
Market-Specific Considerations
Sub-Saharan Africa
African fertilizer markets typically specify standard granular urea 46%N with max 1.5% biuret. Government subsidy programs (Nigeria, Tanzania, Kenya, Ethiopia) have specific procurement requirements — including country-of-origin restrictions in some cases, and SGS inspection at loading port as mandatory.
Middle East
UAE, Saudi Arabia, and Iran have significant domestic urea production and export capacity. Imported urea competes on price; documentation quality and SGS inspection are expected.
Southeast Asia (rice-growing regions)
High-biuret sensitivity is lower for paddy rice broadcast application, but low biuret grades (< 1.0%) are preferred for vegetable and horticulture markets in Thailand, Vietnam, and the Philippines.
How MC International Guarantees Nitrogen Specification
MC International S.P.A Co., Ltd exports granular and prilled urea 46% N with SGS pre-shipment inspection covering all critical parameters. Our standard specification provides a buffer below the commercial limit: we supply at min 46.0% N, max 1.0% biuret, and max 0.3% moisture — tighter than commercial minimum to protect buyers' downstream performance.
Complete documentation includes SGS inspection report, COA from origin manufacturer, safety data sheet (SDS/MSDS), and Certificate of Origin. Phytosanitary documentation available on request for destination countries requiring it.
Request Urea Specifications and Pricing
Contact our fertilizer team for current availability, pricing, and technical specifications.
Email: sales@mcispcoltd.com
WhatsApp: +66 99 437 2193
MC International S.P.A Co., Ltd — SGS Inspected | ISO 9001 | Granular & Prilled Urea | 46% N Guaranteed | 10+ Years | Laem Chabang, Thailand