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not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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Copyright 2005, Board of Trustees, University
FLUORIDE ANALYSIS OF MATERIALS COMMONLY AVAILABLE
AS NUTRITIONAL SOIL AMENDMENTS
C. A. Conover and R. T. Poole
IFAS, University of Florida
Agricultural Research Center-Apopka
ARC-A Research Report RH-81-12 .F.A.S.- Univ. of Forich
Research conducted at the Agricultural Research Center-Apopka, and at
other research centers and universities, has assisted in identification of
foliage plant species which are susceptible to fluoride injury. Foliage
plant species sensitive, or probably sensitive, to fluoride are listed in
Research over the past 10 years has indicated incorporation of super-
phosphate into potting media has been a major factor in fluoride toxicity
of the plants listed in Table 1, as superphosphate contains 1 to 2% (10,000
to 20,000 ppm) total (soluble plus insoluble) fluoride as a contaminant.
Since no unique benefit has been observed from amendment with superphosphate,
we do not recommend its use. Phosphorus can be obtained from other sources
such as ammonium phosphate and phosphoric acid. Superphosphate, however, is
not the sole source of fluorides. Early research with Cordyline terminalis
'Baby Doll' cuttings, probably the most fluoride sensitive foliage plant,
demonstrated that soluble fluoride uptake from irrigation water through the
cut stem during propagation caused tip necrosis of 'Baby Doll' at levels of
0.25 ppm fluoride or more (approximately .000025% or greater soluble fluoride).
Another fluoride source was perlite used to amend propagation media. Although
perlite contains approximately 17 ppm soluble fluoride (.0017%), research
findings indicated the detrimental influence of fresh perlite was of short
duration and that most of the fluoride could be removed through 2 to 3 heavy
leachings prior to use as a soil amendment or by maintaining a pH level of 6.0
to 6.5. Several types of peat moss and other types of potting materials were
found to contain more than 0.25 ppm soluble fluoride. As our research has
shown that fluoride sensitive plants are more susceptible to fluoride damage
when the medium pH is below 6.0, we have recommended elevating medium pH to
between 6.0 and 6.5 by addition of dolomite, calcium carbonate or hydrated
lime at time of preparation. The pH range of 6.0 to 6.5 inhibits plant uptake
of soluble fluoride because insoluble compounds are formed in the potting medium.
At times some growers have observed fluoride injury on fluoride
sensitive crops even though care had been exercised to avoid use of any
known fluoride containing material or water containing fluoride. As
soil amendments other than superphosphate may contain soluble fluoride in
amounts large enough to cause foliar injury, sample of various amendments
were obtained and analyzed for readily soluble fluorides.
A 250 mg sample of each soil amendment was put into 25 ml of deionized
water and diluted 1:1 with total ionic strength adjustment buffer (TISAB).
After 24 hours soluble fluoride concentration was measured with an Orion
404 Specific Ion Meter and a 96-09 electrode. There are other more
commonly used laboratory procedures available for obtaining total fluoride
content of soil amendments, but we utilized this procedure to detect soluble
fluorides which would be available to the plants from the soil amendments
when tested at a pH of 5.5, Fluoride concentration was expressed as mg of
soluble fluoride per kg of soil amendment on a dry weight basis. Results
are listed in Table 2.
These'data indicate water soluble fluoride at pH 5,5 available from the
fertilizer and soil amendments tested; they do not indicate insoluble
fluorides. The test for total (soluble plus slowly soluble) fluorides would
show higher readings for materials like dolomite or superphosphate, since
they are not completely soluble, while materials like diammonium phosphate
seem high because fluorides are 100% soluble. Thus, these data indicate the
potential soluble fluoride effects of using the materials listed in Table 2
rather than total effects. Brand names have been omitted and the same
material from different sources may have different amounts of soluble fluorides.
Consequently, these data identify potential sources of soluble fluorides. The
value of the information in Table 2 relates to making decisions on materials to
utilize as fertilizers or soil amendments when fluoride toxicity problems are
occurring in a nursery.
Items with greater than 100 mg soluble fluoride per kg are considered
high and should not be used where fluoride toxicity is a problem, especially
if large amounts of the amendment are used.
The one real surprise of these tests was the very high level of fluorine
found in diammonium phosphate. If these levels are commonly found in this
source, we would not suggest it as a replacement for superphosphate; rather,
we would suggest use of phosphoric acid.
Table 1. Relative sensitivity of foliage plant species to fluoride contained in
Baby Doll Ti
Table 2. Water soluble fluoride analysis of commonly available soil
mg soluble fluoride/kg
Amendment amendment (dry wt basis)
Diammonium phosphate 2000.0
Triple superphosphate 1600.0
Zinc oxide 733.0
Fritted trace elements 552.0
Sulphate of ammonia 480.0
Resin coated slow release fertilizer 376.0
Sulphate of potash 83.0
Sludge (A) 76.0
Calcium hydroxide 72.0
Cotton hull ash 67.3
Muriate of potash 67.0
Magnesium sulfate (A) 28.0
Ferrous sulfate 21.0
Boron (A) 20.8
Cow manure 17.1
Sludge (B) 16.7
Urea formaldehyde spray 14.2
Urea formaldehyde 10.4
Copper sulfate 8.9
Sulfur-coated urea 7.6
Ammonium nitrate 6.9
Magnesium sulfate (B) 6.9
Chelated iron 6.8
Nitrate of potash 6.6
Magnesium sulfate (C) 5.4
Boron (B) 2.0
Sheep manure 0.8
Cotton seed meal 0.4
Aluminum sulfate 0.2
Our thanks are extended to Florida East Coast Fertilizer Co.,
Homestead, FL 33036 for their assistance in obtaining the soil
amendments listed in this table.
Average of 4 replications.
Conover, C. A. and R. T. Poole. 1972. Factors influencing fluoride induced
necrosis of Cordyline terminalis 'Baby Doll'. Assoc. of Southern Agric.
Workers, Inc. 69:156 (Abstr.).
Conover, C. A. and R. T. Poole. 1976. Fluoride toxicity of tropical foliage
plants. Horticulture Digest (Univ. of Hawaii) 29:2.
Dalton, J. D. 1976. Fluoride in potting media, soils and water in Dade
County, Fl. Fla. Coop. Ext. Serv. Homestead. 3 pp.
Dalton, J. D. 1976. Minimizing fluoride damage. Fla. Coop. Ext. Serv. -
Homestead. 1 pp.
McConnell, D. B. and W. E. Waters. 1971. Central Florida Well Water Analyses.
Florida Foliage Grower 8(2):1-5.
Marousky, F. J. and S. S. Woltz. 1977. Influence of lime, nitrogen, and
phosphorus sources on the availability and relationship of soil fluoride
to leaf scorch in Lilium longiflorum Thunb. J. Amer. Soc. Hort. Sci.
Poole, R. T. and C. A. Conover. 1972. Influence of fluoride on foliar
necrosis of Cordyline terminalis 'Baby Doll'. Proc. SNA Res. Conf.
Poole, R. T. and C. A. Conover. 1972. Necrosis of Cordyline terminalis
'Baby Doll' as influenced by soluble fluoride. HortSci. 7:320 (Abstr.).
Poole, R. T. and C. A. Conover. 1974. Fluoride toxicity of Dracaena 'Janet
Craig'. HortSci. 9:285 (Abstr.).
Poole, R. T. and C. A. Conover. 1976. A list of foliage plants sensitive to
fluoride. Florida Foliage Grower 13(7):5.
Wilkerson, D. C. and G. L. Lingaman. 1978. The effects of fluoride on
Chlorophytum comosum. HortSci. 13(3):12 (Abstr.).
Woltz, S. S. and W. E. Waters. 1977. Susceptiblity of some foliage plants
to fluoride air pollution. Florida Foliage Grower 14(3):5-7.