1. Composition and Manufacturing Process

• Sulfur Coated Urea (SCU):
  • Coating Material: Primarily sulfur, supplemented with microcrystalline wax and attapulgite regulators.
  • Process: Molten sulfur is spray-coated onto urea particles to form a triple-layer structure (base sulfur layer, sealing layer, and regulatory layer).
  • Characteristics: Simple process, low cost, but potential for sudden membrane rupture.
• Polyurethane Coated Urea (PCU):
  • Coating Material: Polyurethane as the carrier, applied via thermal compression wrapping.
  • Process: Urea particles are uniformly coated under high temperature to form a smooth, even membrane.
  • Characteristics: Moisture-resistant, heat-resistant, and aging-resistant; non-polluting after degradation.

2. Performance Comparison

3. Application Performance

• Sulfur Coated Urea (SCU):
  • Advantageous Crops: Corn, rice (yield increase of 9.7–12.4% in Northeast China’s black soil).
  • Limitations: Sulfur benefits reduced by 37% in acidic soils; release curve misaligned with crop demand.
• Polyurethane Coated Urea (PCU):
  • Advantageous Crops: Corn, wheat (full-season fertilizer efficiency >70%).
  • Advantages: Prevents excessive early growth; avoids late-stage nutrient deficiency; enhances lodging resistance; suitable for mechanized fertilization.

4. SWOT Analysis

5. Environmental Impact

• SCU: Sulfur may exacerbate soil acidification; minimal membrane residue.
• PCU: Non-toxic degradation products; enhances soil water retention and permeability.

6. Recommended Use Cases

• SCU: Alkaline/saline-alkali soils; cost-sensitive field crops (e.g., Northeast China corn).
• PCU: Acidic soils; high-efficiency agriculture; crops requiring precise nutrient control (e.g., vegetables, fruits).

Conclusion: Polyurethane Coated Urea (PCU) excels in release precision, environmental sustainability, and adaptability, aligning with modern agricultural demands. Sulfur Coated Urea (SCU) remains viable for cost-driven applications and saline-alkali soil remediation.