Polymer-coated urea

Polymer-coated urea consists of standard urea granules enclosed in a polymer film. The coating slightly lowers the overall nitrogen analysis compared with uncoated urea, to around 44%, and its thickness and formulation determine the release duration, which is engineered for a target number of weeks or months.

Core material

Standard urea granules

Coating

A polymer membrane controlling water entry and nitrogen release

Nitrogen content

Around 44%, slightly below uncoated urea

Release control

Diffusion through the coating, driven mainly by soil temperature

Polymer-coated urea supplies nitrogen only, but releases it gradually. Once the urea diffuses out, it behaves like ordinary urea nitrogen, hydrolysing to ammonium and then nitrifying to nitrate. Because the release is spread over time and temperature-driven, less nitrogen is present at once, reducing the peak exposure to loss pathways.

• Nitrogen is released gradually rather than all at once
• Release rate rises with soil temperature, broadly tracking crop growth
• Once released, nitrogen behaves like conventional urea nitrogen

Polymer-coated urea is used where a single application can replace several splits, such as in cereals, maize, turf, and high-value horticulture, and where reducing nitrogen loss is a priority. It can be applied at or before planting to supply nitrogen through much of the season with fewer field passes.

• Can reduce the number of in-season nitrogen applications
• Aims to lower leaching, volatilisation, and denitrification losses
• Used in cereals, maize, turf, and high-value horticultural crops

Because release depends on temperature, the timing of nitrogen availability may not perfectly match crop demand in every season, and an unusually cool or warm period can shift release earlier or later than intended. Coated products also typically cost more per unit of nitrogen, and the polymer residues left in soil are a growing consideration.