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LS INFLUENCE OF SOIL ACIDITY AND LIMING ON THE PRODUCTION OF LEATHERLEAF FERN
S0-7 \IN HuE LI
D. D. Mathur
i-L tJ,3 Univer ity of Florida, IFAS
ARC-Apopka Research Report RH-1980-7
I.F..S.- niv. of Florid
n acid soil is one that contains more H ions than OH- ions in the
soil solution. In alkaline soils the reverse is true, OH" exceeds H In
a solution the concentration of H+ varies inversely as the concentration
of OH" in such a fashion that the product of the two concentrations is
always constant. When the concentration of one of these ions is determined,
the other is also know. Therefore, only H+ needs to be measured.
Soil acidity may be divided into two kinds "active" and "reserve"
acidity. Reserve acidity may also be referred to as potential or exchangeable
acidity. Taken together, the "active" and "reserve" acidity constitute
total soil acidity. The H+ concentration of the soil solution at any partic-
ular time is relatively small. In humid region soils, the removal from
colloidal fractions of positive ions, especially calcium,occurs constantly
through ion exchange. Their place is taken by hydrogen on the colloidal
complexes of the soil. Such reserves of H+ are designated as the reserve
acidity of the soil solution. The reaction of an acid soil can be influenced
only when enough lime is added to react with H+ (of soil complex) reserve
acidity as well as H+ (of soil solution) active acidity. The greater the
exchange capacity, the greater the reserve acidity and the greater the
difficulty of reducing the acidity of the soil solution. The magnitude of
this resistance to change is called buffer capacity.
Most plants grow best when soil pH is between 6.0 and 7.0, but general
experience has shown that leatherleaf fern requires a soil pH between 5.5
and 6.0. All plant nutrients are available between pH 5.5 and 7.0. In
general, pH and available calcium are closely related; but there are ex-
ceptions especially when sodium is present. Elements such as calcium and
magnesium are especially deficient in acid soils. In strongly acid soils,
aluminum, manganese and iron may exist in toxic quantities because of their
increased solubilities. In addition, these elements may react with phos-
phorus to form insoluble phosphates. In alkaline soils, pH 7.0 and above,
phosphorus, iron, manganese, boron, zinc and copper are usually unavailable
in quantities required by plants. Fertilizer programs for sandy soils
should be applied to maintain a steady pH.
Leatherleaf fern production is concentrated on the central Florida
ridge, which is dominated by 1) well drained to moderately well drained
soils, 2) soils dominantly thick to thin sands influenced by alkaline
materials and 3) soils dominantly thick to thin phosphatic sands and loamy
sands overlying fine textured materials. Under these situations extreme
care should be taken when establishing a new fernery. A soil test is
highly desirable because in some cases liming may not be necessary at the
Liming materials differ in their ability to neutralize acids. The
value of limestone depends on the quantity of acid that a unit weight of
the material will neutralize. This property, in turn, is related to
molecular composition of the liming material, chemical purity, solubility
in water and its freedom from inert contaminants such as clay. Pure
calcium carbonate is the standard against which other liming materials are
measured. The neutralizing value of calcium carbonate is 100 percent.
A list of neutralizing values of common liming materials is shown in
Table 1. Neutralizing value of common liming materials.
Material Neutralizing value (%)
CaCO3 Calcitic limestone 100
CaO Burnt lime 178
Ca(OH)2 Hydrated lime 136
CaMg (C03)2 Dolomitic lime 109
CaO MgO Dolomitic oxide 195
Basic slag 85
Calcium silicate slag 85
Ca = Calcium, Mg = Magnesium, CO3 = carbonate, 0 =
oxide, OH = hydrate.
Mode of action: Mineral clays in soils are of two general classes 2:1
and 1:1. The 2:1 relates to 2 layers of silica and one of alumina (Al) and
1:1 relates'to one layer of silica and one layer of alumina. Liming reaction
in 'each is complex. A soil reaction may be generalized as follows:
Al (Soil) + 3 Ca CO3 + 6H20 > 3 Ca (Soil) + 2 Al (OH)3 + 3 CO2
When lime is added to a soil,Ca ions replace Al ions on the exchange site
through mass action. The displaced Al ions hydrolyze to form gibbsite which
is inert and water and CO2 are formed. Due to the removal of active Al
from the soil complex through precipitation and gibbsite, the increase in
OH ions in the system and the increase in the base saturation of the soil
complex, the soil pH increases. How much lime should be added? The amount
of lime to be added is directly'related to the exchange capacity of soil
or the Feserve acidity.
Experimentation on the effect of dolomite and micronutrients incor-
porated into the soil before planting on the yield of leatherleaf fern has
shown that addition of both dolomite and micronutrients reduced yield. The
addition of dolomite at the rate of 1000 pounds per acre has been a frequent
practice among fern producers.
The raised pH due to the application of dolomite would then adversely
affect the growth and yield of leatherleaf fern. Field observations and
planting history of the leatherleaf fern in DeLand, DeLeon Springs and Lake
County have revealed that application of dolomite when establishing a fernery
has sometimes caused frond burn and reduction in the yield of leatherleaf fern.
The rate of application of two types of lime to two types of soil for 1000
square feet and per acre is reported in Table 2. If on a light, sandy soil you
have a pH of 4 and wish to raise it to pH 6, add 1050 Ibs hydrated lime or 2100
Ibs of ground limestone per acre, if your pH is 5.25, add 300 Ibs hydrated lime
or 600 Ibs ground limestone. On the other hand, if you have a pH of 4.5 and
wish to raise it to 5.5, add 600 Ibs hydrated lime or 1200 lbs ground limestone;
the difference between the two. Most of Florida's lime materials are soft rock
materials which are highly soluble and fast reacting which may be disadvantageous.
Because of the nature of our soils, the long term benefit of our soft materials
may be inferior to lime materials from other states which are harder and less
Readily water soluble hydrated lime and burned lime are the two liming
materials used in the ornamental industry. Both have relatively high
neutralizing values and should be used in smaller quantities than other liming
materials (Table 1). They are caustic and will cause skin irritation. Direct
application to plants may cause foliage burn, Basic slag is a by-product of
the steel industry. It has low neutralizing value as compared to other liming
materials but it also contains phosphorus and other impurities which increase
its value as a soil amendment.
Can gypsum (CaSO4) be used as a liming material? Gypsum, a neutral
salt, is not a true liming material and does not neutralize soil acidity. A
true liming material contains calcium and neutralizes soil acidity, A mixture
of dolomite and gypsum has the capacity to supply calcium, magnesium
Table 2. Approximate rates of application of
for pH adjustment of typical Florida soils
hydrated lime and ground limestone
used to produce leatherleaf fern.1
Light sandy soil (St. Lucie) Medium sandy soil (Lakeland)
Soil Hydrated lime Ground limestone Hydrated lime Ground limestone
Acidity Ibs/ Ibs/ Ibs/ lbs/
(pH) 1000 ft Acre 1000 ft2 Acre 1000 ft2 Acre 1000 ft Acre
4.00 24.1 1050 48.2 2100 32.1 1400 64.3 2800
4.25 20.7 900 41.3 1800 27.5 1200 55.1 2400
4.50 17.2 750 34.4 1500 23.0 1000 45.9 2000
4.75 13.8 600 27.5 1200 18.4 800 36.7 1600
5.00 10.3 450 20.7 900 13.8 600 27.5 1200
5.25 6.9 300 13.8 600 9.2 400 18.4 800
5.50 3.4 150 6.9 300 4.6 200 9.2 400
6.00 None None None None None None None None
Light sandy soil To raise pH 4 to pH 6, add
ground limestone/acre, if pH is 5.25, add 300
limestone. To raise pH from
hydrated lime or (1500 300
1050 Ibs hydrated
Ibs hydrated lime
4.5 to 5.5 use the difference (750
= 1200) Ibs ground limestone/acre.
lime or 2100 Ibs
or 600 Ibs ground
- 150 = 600) Ibs
To find the
amount of lime for 1000 sq ft and medium sandy soil follow the same procedure as
light sandy soil.
2Although use of Table 1 on page 3 would indicate that higher levels of hydrated
lime may be required to change pH, rates in Table 2 are proposed with safety of
the crop in mind since most growers apply hydrated lime through the irrigation
system. One month after application of hydrated lime, check pH again and reapply
and sulfur while at the same time producing a small increase in pH. Addition
of sufficient liming material to supply adequate calcium and magnesium may in-
crease soil pH in such a way as to reduce the availability of essential macro
Reduction time of lime: The approximate reaction time for dolomite according
to the typical mesh sizes found in various grades is given in Fig. 1. By
Florida law 50% of the material must pass a 50 mesh sieve, 80% must pass a
20 mesh sieve and not more than 10% retained on a 10 mesh sieve.
The data in Fig. 1 show that 6 to 9 months reaction time is required
to get maximum benefit from the added lime. One could not expect to obtain
maximum benefit from lime applied immediately before planting, but, some
benefit may be obtained from the added Ca and/or Mg thus it is never too late
to add lime. The above data was obtained by using dolomite but in Florida
high solubility liming materials are available which react faster than dolomite.
To decrease soil pH wettable sulfur usually is added. One milliequivalent
of sulfur (0.016 gram) by oxidation will form 1 milliequivalent of sulfuric
acid. On that basis 1 pound of elemental sulfur will produce an amount of
acid whose neutralization will require 3 pounds of calcium carbonate. Gen-
erally it takes approximately 1/3 the amount of wettable or super-fine sulfur
to decrease pH 1 unit as it does ground limestone or dolomite to raise pH.
In other words, divide the amounts listed for a particular soil type in Table
2 by 3 to determine the amount of wettable or super-fine dusting sulfur needed
to acidify the soil 1 pH unit. Not more than 5 pounds per 1000 ft2 should be
used in 1 application because in soil sulfur oxidizes and mixes-with water
to form a strong acid that can burn the roots of plants. Reapply in 8 weeks
or more if pH is not at desired level.
6.0 s o
5.5 9.0 10 %
0 6 12 18
Effect of mesh size on reaction time or lime.
1. Baker, A. S. 1970. The degree of mixing of lime affects the
neutralization of exchangable aluminum. Soil Sci. Soc. Amer. Proc.
2. Coleman, N. T., E. J. Kamprath, and S. B. Weed. 1958. Liming.
Advan. Agron., 10:475.
3. Coleman, N. T., and G. W. Thomas. 1967.- The basic chemistry of
soil acidity. In: R. W. Pearson and F. Adams (eds.) Soil Acidity
and Liming. Agronomy 12:1-41. Amer. Soc. of Agron. Madison, Wis.
4. Duncan, J. M. 1951. The lime industry in Florida. An intangible
analysis. Eng. Progress of the Univ. of Florida. Vol. V., No. 12.
Supplement, Fla. Eng. and Ind. Exp. Sta.
5. Hopkins, R. H. 1942. The dolomite limestones of Florida. Florida
State Board of Conservation. Florida Geological Survey. Report of
Investigation No. 3.
6. Jackson, M. L. 1960. Structural role of hydronium in layer silicates
during soil genesis. Int. Congr. Soil Sci., Trans 7th (Madison, Wis.,
USA). Vol. II, 445-455.
7. Keeney, D. R., and R. B. Corey. 1963. Factors affecting the lime
requirements of Wisconsin soils. Soil Sci. Soc. Amer. Proc. 27:277-280.
8. McLean, E. 0. 1970. Lime requirements of soils inactive toxic sub-
stances or favorable pH range. Soil Sci. Soc. Amer. Proc. 34:363-364.
9. Perkins, H. F. 1963. Lime-comparison between different sources of
lime. New Developments in Fertilizer and Lime, November 6'and 7,
Rock Eagle, Georgia.
10. Poole, R. T. and C. A. Conover. 1973. Influence of dolomite and
micronutrients on yield of leatherleaf fern. Proc. Fla. State Hort.
11. Shaw, W. M., and B. Robinson. 1959. Chemical evaluation of neutralizing
efficiency of agricultural limestone. Soil Sci. 87:262.
12. Shaw, W. M. 1961. Rate and reaction of limestone with soils. Soils
13. Schollenburger, C. J., and C. W. Whittaker. 1962. A comparison of
methods for evaluating activities of agricultural limestones. Soil
14. Whittaker, C. W., M. S. Anderson and R. F. Reitemier. 1951. Liming
soils for better farming. USDA Farmers Bull. No. 2032.
15. Whittaker, C. W., C. J. Erickson, K. S. Love and D. M. Carroll. 1959.
Liming qualities of three cement kiln flue dusts and a limestone in a
greenhouse comparison. Agron. J. 51:280.
16. Woodruff, C. M. 1948. Testing soils for lime requirement by means of
a buffer solution and the glass electrode. Soil Sci. 66:53-63.