Translations:Controlled-release fertilizer/3/en

In the 1960s in the U.S., the Tennessee Valley Authority National Fertilizer Development Center began developing sulfur-coated urea. Sulfur was used as the principal coating material because of its low cost and its value as a secondary nutrient. Usually wax or polymer is added to perfect the encapsulation. The slow-release properties depend on the degradation of the secondary sealant by soil microbes as well as mechanical imperfections (cracks, etc.) in the capsule. 6 to 16 weeks of delayed release in turf applications is typical. When a hard polymer is used as the secondary coating, the properties are a cross between diffusion-controlled particles and traditional sulfur-coated.