Bruce J. Augustin, A. E. Dudeck, and
Charles H. Peacock
Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
John T. Woeste, Dean for Extension
9ruary au i--rcular /ui
/ Hu;^ LiBRA5R
Saline Irrl tion Flori
of Florida Turfgrasses
Saline Irrigation of Florida Turfgrasses
Bruce J. Augustin, A. E. Dudeck, and Charles H. Peacock*
Turfgrass irrigation has become a major cultural practice
throughout Florida. Providing adequate supplemental water insures
a consistent, healthy, vigorously growing landscape when rainfall
is inadequate or infrequent. Obtaining ample quantities of good
quality water is becoming difficult as irrigation demands increase
and fresh water supplies dwindle. Often lower quality water with high
amounts of dissolved soluble salts is used in order to obtain adequate
amounts of irrigation.
Irrigation Water Quality
The principal soluble salts found in water are the chloride and
sulfate salts of sodium, calcium, and magnesium. Other salts are
found in lesser amounts. The original source of these materials was
from weathering of primary rocks and minerals. Oceans have become
the eventual reservoir of soluble salts as water has moved through
the hydrological cycle. Along coastal regions of the country, seawater
is intruding into fresh water supplies and contaminating them by
increasing the level of soluble salts. In interior regions of the country,
ancient saline marine deposits in geological layers add soluble salts
to groundwater as it passes through the layers. This process has oc-
curred throughout the country and virtually all fresh water supplies
have some amount of dissolved salts. The amount of salts in water
determines the degree of salinity and to a large extent the overall
Salinity is determined by a meter which measures the electrical
conductivity (EC) of a water sample. This is determined as the inverse
of the resistance of an electric current as it is passed between two
probes in a solution. Electrical conductivity is determined in units
*Extension Turfgrass and Water Specialist, Fort Lauderdale Research and
Education Center; Turfgrass Research Scientist and Extension Turfgrass
Specialist, Ornamental Horticulture Department, Institute of Food and
Agricultural Sciences, University of Florida.
of Siemens per meter (S/m) or in the older units of mhos per centi-
meter (mhos/cm). Generally, electrical conductivity is reported in
tenths of Siemens or deciSiemens per meter (dS/m) which are equal
to the old reporting unit of millimhos per centimeter (mmhos/cm).
Electrical conductivity expressed in dS/m is the preferred salinity
measurement because it represents the total salinity that may be
associated with possible salt stress on plants from saline irrigation.
Electrical conductivity and concentration of dissolved salts (in
parts per million, ppm) are directly related units depending on the
salts present. A sodium chloride solution of 1 dS/m is equal to 640
ppm soluble salts. Other salt solutions vary from 550 to 700 ppm
for every 1 dS/m. Water sample salinities are often compared to those
of seawater which has an average EC of 43.0 dS/m and about 32,000
ppm dissolved salts.
Irrigation water has been classified into four categories based on
the salinity hazard (Table 1). These limits were determined by the
U. S. Salinity Laboratory based on the relationship between electrical
conductivity of water and electrical conductivity of soils to which
the water has been applied. Water with EC readings of less than 0.75
dS/m is suitable for irrigation without any problems. Successful use
of water with EC values above this level depends upon soil conditions
and plant tolerance to salinity.
Quality of irrigation water is also influenced by other specific ions.
The amount of sodium is of prime concern because it is often found
in the largest amount. Excessive sodium destroys soil structure.
Sodium is also an antagonistic ion which displaces potassium and
can limit availability of iron, manganese, and phosphorus in soils.
Boron in irrigation water is rarely a problem with turfgrasses because
boron accumulates in leaf tips which are removed by regular mowing.
Other landscape plants may be more sensitive to boron levels. High
Table 1. Classification of Saline Irrigation Water.
Salinity Electrical conductivity Concentration of
class (dSIm) dissolved salts (ppm)ommen
Low <0.25 <160 Low salinity hazard
Medium 0.25 0.75 160 480 Some leaching
High 0.75- 2.25 480- 1440 Good drainage
required and salt-
Very high >2.25 >1440 Excellent drainage
required and very
concentrations of chloride, sulfate, and bicarbonate ions can cause
specific injury under certain soil conditions.
Table 2. Recommended Irrigation Amounts for Saline Water.
Irrigation water Maximum plant salinity tolerance level, measured
EC (dS/m) by saturated soil paste extract (dS/m)
4 (Low) 8 (Medium) 16 (High)
(inches of water required to replace weekly
evapotranspiration losses and provide
adequate leaching in rootzone)
0.00 1.5 1.5 1.5
1.00 2.0 1.7 1.6
2.00 3.0 2.0 1.7
3.00 6.0 2.4 1.8
Influence of Saline Irrigation on Soils
Soils are a key to the continued use of saline irrigation water. Good
drainage is essential to leach soluble salts through the soil profile.
The better the drainage, the more successfully proper saline irrigation
can keep the soil level of soluble salts within tolerable limits. Soil
texture has a major influence on use of saline irrigation water. Sand-
textured soils have a low moisture-holding capacity and will concen-
trate soluble salts quicker than fine-textured soils as moisture is lost
by evapotranspiration. Sand soils are usually best suited for saline
irrigation because of easy drainage, but they must be maintained
at field capacity in order to prevent intolerable salt levels.
Soluble salts are measured in soils by the same basic method as
water samples. A conductivity instrument measures the electrical
conductivity from a saturated paste extract from a soil. The IFAS
Soil Testing Laboratory uses a dilution of one part dry soil to two
parts water. The electrical conductivity readings of soils are two to
ten times greater than the irrigation water applied to them. Soils
with EC readings of 2.0 to 4.0 dS/m are considered to have low salt
levels. Soils with EC readings of 4.0 to 12.0 dS/m have medium levels.
When soil readings are above 12.0 dS/m, soils are considered to have
high salt levels.
To maintain a certain salt level in the soil, saline water must be
applied at rates exceeding evapotranspiration to leach excess salts
through the soil (Table 2). For example, to replace 1.5 inches of water
lost by evapotranspiration (approximately a week's worth of plant
water use) rainwater with 0 dS/m would not increase the salinity,
so 1.5 inches of irrigation would be sufficient. However, greater
amounts of saline irrigation must be applied because of the tendency
to concentrate salts in the soil. Leaching with large amounts of saline
irrigation water keeps soil salts at tolerable levels because excessive
salt is removed from the rootzone. Rainfall is extremely beneficial
when saline water is used for irrigation because it will aid in leaching
and diluting soluble salts.
Effect of Salinity on Plants
Saline water can cause salt stress and injury to plants by several
means. Direct salt injury occurs with the accumulation of salts in
the soil as well as ion accumulation within the plant. Reduction in
plant growth and other metabolic processes such as photosynthesis
is primarily a result of water stress. The ability of saline soils to hold
water more tightly results in greater plant water stress. This indirect
osmotic stress causes dehydration of the plant by removing water
from the plant into the soil because of a salt concentration gradient.
Plant nutrient deficiencies are indirectly caused by suppression of
nutrient absorption. The most common example of this is the antago-
nistic effects of sodium on the uptake of potassium into the plant.
Plant resistance to salt stress varies greatly. Some plants avoid
salt stress by either excluding salt absorption, extruding excess salts,
or diluting absorbed salts. Other plants tolerate salt stress by adjust-
ing their metabolism to withstand direct or indirect injury. In most
cases the mechanism of salt tolerance in plants is a combination of
The effect of high salt levels on turf can be observed by a number
of visual symptoms. There is a tendency for the turf to wilt faster
than normal as a result of osmotic stress. Shoot and root growths
are reduced at high salt levels through both direct and indirect salt
injury. Leaf tipburn and a general thinning of the turf are also com-
mon symptoms. Severe salt stress will ultimately cause turf death.
Table 3. Salt Tolerance of Turfgrass Species.
Salt tolerance Species EC at 50% yield reduction
Excellent Zoysiagrass 37
Seashore paspalumgrass 26
St. Augustinegrass 24
Good Tall fescue 13
Perennial ryegrass 12
Fair Creeping bentgrass 10
Table 4. Salt Tolerance of Various Bermudagrass Cultivars.
Salt tolerance Bermudagrass
Salt Tolerance of Turfgrasses
Turfgrass species have been classified according to salt tolerance
(Table 3). Most turfgrass comparisons are based on the salt levels
which cause a 50% reduction in top or root growth. Only a few species
grow well under saline conditions. Zoysiagrass, seashore paspalum-
grass, and bermudagrass are the best species to grow in Florida if
irrigation is limited to saline water. These grasses require good drain-
age and moist soil conditions to produce good quality turf. Adequate
leaching is essential, whether it is from rainfall or excess saline irriga-
tion. Because of nematode and insect pest problems with these turf-
grasses, maintenance necessities need to be carefully considered
Cultivars within a species often show a wide range of salt tolerance
(Table 4). Sometimes cultivar differences are greater than species dif-
ferences. Tifdwarf and Tifgreen are the most salt-tolerant bermuda-
Saline Irrigation Guidelines
A few simple guidelines should be followed to grow plants success-
fully using saline irrigation.
Use the best quality water available.
Provide excellent drainage to remove salts from rootzone.
Use excess saline irrigation to maintain desired soil salt level and
to leach salts.
Aerify, spike, and vertically mow to keep Water infiltration rates
Monitor soluble salts routinely in soils and irrigation water.
Use the most salt-tolerant turfgrass for your location.
This publication was produced at a cost of $820.75, or 10.7 cents per
copy, to inform the public on irrigation water quality and its effects on
COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORI-
DA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES, K. R.
Tefertller, director, In cooperation with the United States Department IFAS
of Agriculture, publishes this Information to further the purpose of the
May 8 and June 30, 1914 Acts of Congress; and Is authorized to pro-
vide research, educational Information and other services only to indi-
viduals and institutions that function without regard to race, color, sex or national ori-
gin. Single copies of Extension publications (excluding 4-H and Youth publications) are
available free to Florida residents from County Extension Offices. Information on bulk
rates or copies for out-of-state purchasers is available from C. M. Hinton, Publications
Distribution Center, IFAS Building 664, University of Florida, Galnesvllle, Florida
32611. Before publicizing this publication, editors should contact this address to deter-