2. The second major category includes renowned water soluble
fertilizers with physical barriers that control nutrient release. These
appear either as granules/cores coated with a hydrophobic polymer,
or as a matrix of active fertilizer nutrients dispersed on a continuum
via hydrophobic material that encumbers fertilizer dissolution.
However, controlled release matrices are less common compared
to coated CRFs, which is why this paper is focused on controlled
release coated fertilizer that contain only urea. Coated granular CRFsare subcategorized to those coated with organic polymer materials
(e.g. thermoplastics, resins etc.) and those coated with inorganic
materials (including sulfur and otherminerals). The controlled release
matrix material can be either hydrophobic e.g. polyolefin, rubber etc.,
or gel forming polymers sometimes referred to as a hydrogels. A
hydrogel is hydrophilic and the dissolution of fertilizer dispersed
through hydrogel material is impeded by its ability to retain high
amounts of water (swelling).