also able to retain both micro and macronutrients within the helical
polymer chainmatrix [34]. Despite these advantages, polymermaterials
do have limitations. The coating processes are quite complex and
involve a number of chemicals. The overall process does not attract
commercial attention because of the high cost as most polymer materials
require the use of organic solvents to formulate a coating solution.
This not only increases costs due to solvents and their recovery, but also
poses adverse environmental impacts in terms of hazardous emissions.
Furthermore, many, if not all polymer coatings, are non-biodegradable
after total nutrient release and present a new type of soil pollution
that is undesirable. Hence, most controlled release urea fertilizers
produced thus far have not been effectively admitted to commercial
production. Even so, certain polymers have been employed to produce
controlled release urea on a commercial scale; a glimpse of these is
given in the next sections.