Plantation Field Laboratory Mimeo Report PFL68-1 December!1967
THE USE OF WET OXIDIZED SEWAGE RESIDUE AS A MULCHq AROUND
ORNAMENTAL PLANTS!'/ JAN 2 1-333
Thomas Cochisa1, F
1 .F.AS. !n;v. of Fic do
S A new form of sewage sludge residue (Zimpro residue) is available in many
areas of the United States and is soon to be available in the Fort Lauderdale,
Florida area. This new method of sewage treatment has been devised by the
Zimpro Division of the Sterling Drug Company. This process leaves a residue
that is paper-like in appearance, which is then ground to most any particle size
needed. This material is "fluffy", light weight and light brown in color when
dry. When it is wet, it is dark brown and looks very much like a soil that is
high in organic matter.
According to tests using soil analysis procedures of the Everglades Station
Soil Testing Laboratory, the sludge is low in extractable N and K and relatively
high in P and Mg. It has a soluble salt content of about 150 ppm (expressed as
NaCI) and a pH of 5.3. This low pH is very desirable in areas of Florida with a
high soil pH and a high pH of irrigation water. In areas of the country where
the pH is low, the acidity of the residue can be modified during the processing.
Because of the texture, organic matter content, pH and nutritional value of
the residue, it appeared that it would make a good mulch for ornamental plants.
It had never been tested as a mulch and it was desirable to see what effect this
material would have on plant growth, and whether or not it would be a practical
material from the standpoint of physical appearance.
Because the sludge is subjected to temperaturesof over 300 degrees F. during
processing, it is sterile and presents no public health problem. There is no
undesirable odor to the product, which might prevent its use around the home.
When the material is fresh it possesses a "damp" paper odor, but even this dissi-
pates shortly after use. Like any sterile material, a saprophytic mold may grow
on it when it is first used. However, if this does occur, it usually disappears
after a few days. There is no danger from this mold if it does appear since it
is non-pathogenic to plants. This same mold grows on freshly sterilized soil
and is not a new phenomenon to horticulturists.
This material produces no phytotoxicity to plants. In fact, because of the
low soluble salt content, it can be used with complete safety around plants.
When surface applied to a depth of about 3 inches, the material provides excellent
weed control and control of loss of water from the soil by evaporation. Because
of its water holding properties and high organic matter content, it is a very
useful material in the sandy soils of south Florida.
1/ This work was supported in part by the Zimpro Division of Sterling Drug
2/ Presently Professor of Biology, Jacksonville State University, Jacksonville,
Alabama, formerly Assistant Ornamental Horticulturist, University of Florida,
Plantation Field Laboratory, Fort Lauderdale. This work was conducted at
Plantation Field Laboratory.
This "wet oxidized" sewage residue has beeniused as a mulch around Hibiscus
rosa-sinensis, Nurraea exotica, Pittosporum tobira and Acalypha wilkensiana,
and presents an attractive appearance when used as a mulch around ornamentals,
Because this residue has no objectionable odor, is sterile (no public health
problem involved in its use) and is nn-toxic to plants disposal is no problem
as it is with other forms of sewage sludge residue. It appears.to have a definite
economic and practical place in agrIiulture. The material is so inexpensively
available in large quantities that it would even be practical to use it asa soil
amendment on a large acreage basls t :
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