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The Reclamation of Turf and Landscaped Areas Following Hurricanes
or other salt-water flooding events.
The surge of salt water brought inland by a
hurricane or other strong storm event has the potential to cause much damage to turfgrass
on landscaped areas. In general, much of the plant material will be severely damaged or
entirely killed by salt damage. Halophytic (salt-tolerant) turf and plants have
specialized adaptations to tolerate and withstand salt water inundations.
For the purposes of clarity, salinity and
salt refers to all salts. These salts are various ionic species such as commonly occurring
calcium, magnesium, potassium and sodium or less commonly iron, zinc, aluminum, manganese,
ammonium, etc. These are the cationic (+ charged) species. The cationic species form salts
in combination with anionic (- charged) species. Anionic salt species commonly include
sulfates, chlorides, nitrates, phosphates. The combination of salt species results in
variable solubilities and therefore effects the commonality of the salts found in natural
water sources. Sodium, is a special case among the salt species. It has far reaching
detrimental effects in soils and can alter the soil ecology such that the soil becomes
slowly permeable and waterlogged. Do not confuse the terms ‘salts’ and
‘sodium’. The inclusion of the term salt does not specify that it is sodium
salt. The use of gypsum referred to later in this article is the utilization of salt.
Gypsum is simply the sulfate salt of calcium.
On high trafficked landscapes such as
athletic fields and golf courses, it is desirable to quickly reduce or eliminate the
effect of the salts and reduce the harmful effects of sodium. Some resource references
advocate the use of sodium free, fresh water to leach salts from soils. However, if
freshwater is utilized for leaching, the hazard of sodium goes up quite dramatically. This
is because sodium is not leached out of the soil at the same rate as the other salts. On
medium or heavy textured soils, the use of freshwater for reclamation (leaching) may turn
the soil from a condition known as saline-sodic soils to sodic soils. The sodic soil is
one in which the soil particulates become dispersed and the soil structure collapses. The
result is a massive soil that has very low permeability and is not likely to provide a
good growth medium. Once the soil becomes dispersed, it is very difficult to reclaim as
the low permeability restricts the leaching of the sodium. Once sodium is leached, the
soil still suffers from destruction of the natural soil structure. The solution for soil
reclamation of salt water or seawater flood damaged landscapes is to use high salt but low
sodium water for leaching.
When dealing with reclamation following tidal
inundations, the following steps may prove helpful.
1. Test irrigation water sources for
salinity. Pump out the lakes and reservoirs that are contaminated with salts from the
seawater tidal surge. The water from these reservoirs may be applied to the areas already
affected by the salt water flooding. Locate a source of water that has least been affected
by salt water intrusion. This fresher water can then be enriched with non-sodium salts and
used for reclamation purposes. DO NOT APPLY FRESH WATER
INDISCRIMINATELY
TO SOILS THAT HAVE BEEN FLOODED WITH SEAWATER OR SALT WATER.
2. Turfs differ in there tolerance to
salinity. To strictly reduce or eliminate the damage to the turf following seawater
flooding, the use of halophytic turfs may be desirable. Fine textured varieties of the
halophytic turfgrasses seashore paspalum and seashore dropseed are currently available.
Bermuda, zoysia, creeping bent, and St. Augustine turfgrasses have good salinity
tolerance. Tall fescue and perennial ryegrass have medium salinity tolerance. Kentucky
bluegrass has poor relative salinity tolerance.
3. In general, repeated irrigation with water
containing 1000 ppm or more total soluble salts will be harmful to the non-halophytic
turfs unless followed by sufficient rainfall or fresh water irrigation. Even irrigation
water containing 500 ppm total soluble salts, if not sufficiently leached, can create soil
salinity levels detrimental to the turf. Halophytic turfs on the other hand, have
been successfully maintained with seawater irrigation (30,000 ppm total salts). In a
situation following flooding with seawater, reclamation of the soil should take precedence
over activities intended to reduce damage to the turf. Once the soils are reclaimed,
the turf can be rapidly reestablished without long term lingering effects. Once a
salt-affected soil becomes sodic, the turf will suffer from years of poor quality as the
soil is slowly reclaimed using aeration and gypsum applications.
4. Soluble salts should be utilized to enrich
the salinity of the reclamation water. Sources of calcium and magnesium salts are the most
commonly available soluble forms of salts. Of course, avoid any salts containing sodium
(Na) and do not over apply potassium (K). Potassium can have a similar but much less
drastic effect on soils as sodium. Acceptable salts would be the chloride, sulphate,
nitrate salts of calcium and or magnesium. Limestone sources should not be used and have
very low solubility anyway. Ideally, these salts would be added to the irrigation
impoundments and solubilized in the water prior to application. Alternatively, these
materials can be applied to the surface and watered in if done carefully. If the soil
contains appreciable calcium and/or magnesium in the mineral form, acid injection of the
irrigation water can liberate these ions into the soil solution and reduce the need for
salt enrichment of the reclamation water. The level of salinity needed in the irrigation
water is dependent upon the extent of salinity and sodium contamination in the soil and
the level of sodium already in the water to be used for reclamation. Higher concentrations
of salt will result in the more rapid removal of sodium. In general however, the total
salinity of water used for reclamation should be at least 1000 ppm TDS if little sodium is
in the water. The determination of salinity requirements for reclamation using water
containing sodium should be determined by a reclamation specialist following testing of
the soils and water.
5. For extended maintenance of soil sodium
levels, gypsum (calcium sulfate) can be used to help leach sodium from the soil. Gypsum
works best when incorporated into the soil, but it can be broadcast on the surface.
Irrigate after gypsum application to move it into the soil. Excess irrigation can be
applied in the following few days to leach the sodium below the root zone. Core
aerification or deep tine aerification can be helpful to improve infiltration and
percolation of water allowing for the removal of sodium. However, this method of sodium
management should not be utilized indescriminantly on a long term basis. The removal of
sodium and the subsequent accumulation at lower depths may create a layer of poorly
drained soils. This may create a situation where the soil becomes overly wet and near
saturated in the root zone portion of the soil as well. The sodium and salts in the saline
coastal environment must be carefully managed and monitored.
6. Soil ecology issues apply to the
management of landscapes on salt-affected sites. For sustainable maintenance of these
sites, careful consideration of the soil ecology must be applied. The levels of total
salts and sodium are only a part of the information need for management of these
landscapes. The soils must be carefully monitored and managed to assure a high
oxidation-reduction potential (re-dox) to support a high quality landscape. The re-dox
potential of the soils should be known and monitored as well as the affects of management
practices and soil amendment applications on the redox potential. Commonly, sulphur is
promoted as a management aid for salinity. This is a sulphur in the elemental form, or as
gypsum or sulphuric acid. However, without proper aeration and drainage conditions, the
application of sulphur containing compounds can exacerbate low soil re-dox states and
promote the production of phytotoxic hydrogen sulphide gas (rotten egg smell). For the
development and management of saline landscape sites, the use of experienced experts in
this area is critical.
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