You may go for either Gel electrophoresis or Paper chromatography or Fingerprinting i.e. 2-dimentional electrophoresis + chromatography

You might allow the urea to diffuse, perhaps  with a urease impregnated  paper, or spray with the urease after diffusion, then spray with any reagent for ammonium ion.  

Hello

Sulfur coated urea fertilizer (SCU) as slow-release fertilizer with high efficiency and a very large benefits for the soil and plants, the agricultural industry has many applications.Also according to the sulfur coated urea by changing the operating parameters and different process conditions and use of sealants, the possibility of producing products with different percentages of sulfur and sulfur-coated urea different dissolution rates there.The use of sulfur coated urea with the least quality (maximum seven day dissolution rate) is far more effective and is more efficient than urea (with fifty-second dissolution rate).

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