Environmental Engineering Reference
In-Depth Information
Urea
Sulphur
Polymer sealant
Outer shell
Fig. 5.5. A pellet of sulphur-coated urea.
provides specific product information and lists the product's compos-
ition, time of release, etc.
Sulphur-coated urea (SCU) is produced when granulated urea is
passed through a stream of molten sulphur, with which it becomes
coated. A wax coating is often applied in addition to sulphur to protect
the surface from microbial degradation. Sulphur-coated urea is a rela-
tively low-cost slow-release nitrogen source. The rate of diffusion of urea
from the coated granules depends upon the thickness and integrity of the
coating. The thicker the coating, the slower the release will be.
Manufacture of resin (or plastic)-coated urea uses a technology simi-
lar to that for sulphur coating. Other soluble nitrogen sources besides
urea, such as nitrate and ammonia sources, are also resin coated. Release
of nitrogen from resin-coated products depends on osmosis through the
semipermeable resin coating rather than on coating imperfections as in
sulphur- or polymer-coated products. Plastic-coated urea works on the
same principle as the resin-coated product. Both resin- and plastic-coated
products have more predictable release characteristics than sulphur-
coated products and give turf managers a high degree of control over
nitrogen release.
Methylene urea
The chemical combination of urea and formaldehyde creates urea-
formaldehyde compounds commonly referred to as methylene urea fer-
tilizers. These products occur as polymers of varying length. The
smaller the ratio of urea to formaldehyde, the longer the chain of polymers
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