Fertilizer-grade urea (FGU), accounting for >50% of global nitrogen fertilizer consumption (IFA 2023), is systematically categorized based on physical properties, chemical composition, and functional enhancements. This classification directly impacts agronomic efficiency, handling safety, and environmental performance.
I. Core Classification by Physical Form
(Governed by ISO 8156:2004 Section 4.1)
| Type | Particle Size | Bulk Density | Key Applications |
|---|---|---|---|
| Prilled Urea | 1.0–2.4 mm | 720–750 kg/m³ | Broadacre crops (wheat/corn) |
| Granular Urea | 2.0–4.75 mm | 760–800 kg/m³ | Precision farming, blends |
II. Chemical Specification Grades
(Based on Biuret Content & Nitrogen Purity)
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Standard Agricultural Grade
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N Content: 46.0% min (dry basis)
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Biuret: ≤1.0% (ISO Grade A)
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Moisture: ≤0.5%
*Trade Designation: UF-46 (Fertilizers Europe)*
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Low-Biuret Grade
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Biuret: ≤0.5% (ISO Grade B)
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Applications: Foliar sprays, horticulture
Example: US EPA-registered foliar formulations
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Ultra-Pure Grade
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Biuret: ≤0.3%
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Heavy Metals: <10 ppm Cd
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Use: Hydroponics, specialty fertilizers
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III. Functionally Enhanced Urea
A. Slow-Release Technologies
| Coating Type | Release Duration | N Efficiency Gain |
|---|---|---|
| Polymer-coated (PCU) | 2–12 months | 25–40% vs. conventional |
| Sulfur-coated (SCU) | 6–10 weeks | 15–30% |
| *Standard: EN 13266 Controlled-Release Fertilizers* |
B. Stabilized Urea
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Inhibitors Added:
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Nitrification inhibitors (DCD, DMPP): Delay NH₄⁺→NO₃⁻ conversion
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Urease inhibitors (NBPT): Reduce NH₃ volatilization by >50
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IV. Regional Classification Variations
A. North America (AAPFCO Standards)
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Type 1: Granular (TGU) – >90% >6 mesh
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Type 2: Prilled (TPU) – >90% <8 mesh
B. European Union (Fertilizing Products Regulation 2019/1009)
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PFC 1(C)(I): Solid inorganic macronutrient fertilizer
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Requires <0.9% biuret for unrestricted use
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C. India (FCO 1985 Amendment)
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Grade I: 46% N, <1.5% biuret
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Grade II: 41% N (for industrial blends)
Quality Control Parameters
All fertilizer-grade urea must comply with:
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Physical Testing:
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Particle size distribution (ISO 8397)
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Crushing strength (ISO 5310)
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Chemical Assays:
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Kjeldahl nitrogen (AOAC 955.04)
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Biuret spectrophotometry (ISO 18643)
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Conclusion
Understanding urea classification is critical for:
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Farmers: Matching product to crop needs (e.g., PCU for rice paddies)
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Traders: Navigating customs codes (HS 310210)
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Producers: Optimizing prill vs. granule production costs
The ongoing shift toward enhanced-efficiency urea (EEU) will drive new classification frameworks, with ISO TC134 currently developing standards for inhibitor-containing fertilizers.
