Thursday, May 15, 2008

Landscape and Turf - Salt Water Inundation Along the Coast

Coastal communitites throughout Delaware were flooded in areas with tidal surges during the recent storm. Soils in these areas were inundated with salt water. This will create saline soil conditions. The following is information on soils and salinity.

Concentrated sodium (Na), a component of salt, can damage plant tissue whether it contacts above or below ground parts. High salt levels also damage plants by osmotic effects, drawing moisture out of plants. High salinity can reduce plant growth and may even cause plant death. Care should be taken to avoid excessive salt accumulation from any source on tree and shrub roots, leaves or stems. Sites with saline (salty) soils present challenges to landscapers and homeowners.

Saline Soils

Saline soils occur when salts accumulate in the soil. Significant aline soils do occur in specific situations such as: along the coastline where seawater may overwash, and where salt from spray may collect in the soil (this happened during the recent storm; along brackish tidal rivers and estuaries. Flooding during storms and high tides can deposit salt in low-lying areas. Wooded wetlands are frequently found in these locations (again, this happened during the recent storm; and in areas with high groundwater tables where salt water has intruded from the bay or marsh areas.

How do saline soils affect trees and shrubs?

Plant root cells contain a membrane which allows water to pass through, but which prevents salt from entering. As the soil's salt content increases, it becomes more difficult for water to pass through the membrane into the root. In addition, if salt levels get high enough they may actually dehydrate roots or cause "salt burn" by drawing water out of root cells. Sodium from sea water also has direct toxic effects on many plants.

High levels of soluble salts also cause changes to soil structure, resulting in compacted soils that are problematic for plants. Because salts bind with soil clays, causing them to swell, compaction occurs more frequently in clayey soils than in sandy soils. Compaction causes reduction of pore spaces between soil particles, reducing water and oxygen penetration into the soil, and water drainage from the soil. As a result, water and oxygen availability to plant roots, and consequently plant growth and pest resistance, is affected.

Plants vary in their ability to grow in salty soils. Plants that grow only in saline soils are called "halophytic" or salt loving. Halophytic plants are generally found in coastal areas, in salt-water marshes, and in brackish (moderately saline) wetlands. The presence of some of these plants (such as spartina and sea oats) is generally indicative of a saline soil.

Most landscape plants are sensitive to soil salinity. Seedling trees and shrubs and young transplants can be particularly sensitive to salt exposure. The severity of salt damage to plants depends upon the amount and duration of exposure, and the concentration of salt. For example, coastal areas that receive consistent salt spray may always have elevated levels of soil salinity. Areas subject to flooding by brackish water or overwash from the Delaware Bay may only be affected by salinity following storms and high tides.

If there is adequate precipitation to leach the salt out of these areas soon after the initial exposure, the amount and duration of salt exposure will be brief. If salt exposure persists, or is repeated, damage will be more severe. There is a direct relationship between the amount and duration of salt exposure and potential damage to plants. The higher the amount of salt in the soil, the greater the impact on plants. Salt damage is generally more severe during periods of hot, dry weather.

Measuring soil salinity

The amount of salt in the soil can be measured with a soil test. The Delaware Cooperative Extension Service Soil Test Laboratory can test for soluble salt levels. With the exception of very salt sensitive plants, most landscape plants can tolerate salt concentrations in the medium or low ranges.

Symptoms of saline soil damage

Plant damage due to saline soils becomes evident more slowly than plant damage due to salt spray. At elevated levels, soil salts are harmful to seed germination and plant growth. General symptoms include stunted growth and reduced yields. All parts of the plant, including leaves, stems, roots and fruits, may be reduced in size. The signs and symptoms displayed by deciduous and broad-leaved trees and shrubs include leaf necrosis (death), marginal leaf or needle burn, leaf drop, and eventual plant death. Entire leaves can be affected and drop prematurely. Buds may fail to open or grow, and branches may die. Sometimes deciduous trees may exhibit early fall color and leaf drop. Salt damage on deciduous trees and shrubs usually becomes evident in late summer following the growing season, or during periods of hot, dry weather (summer drought).

On conifers (firs, junipers, pines, spruces), damage appears as brown needle tips. The brown discoloration progresses toward the base of the needles as salt exposure increases. Salt damage on evergreen trees and shrubs [both conifers and broadleaf (hollies, photinia, southern magnolia)] usually first appears in late winter to early spring and becomes more extensive during the growing season. In extreme situations, trees and shrubs will die due to soil salt damage.

When trying to diagnose plant damage, keep in mind that all of the above signs and symptoms can also be caused by a variety of other factors including root damage, drought, diseases, chemical misuse, etc. Try to eliminate these other possibilities, and use tools such as soil and water analyses, and weather data to help you arrive at a correct damage diagnosis.

Reducing soil salinity or soil salt damage

Numerous options exist for reducing salt damage including:

Improving soil structure, drainage and moisture holding capacity by adding organic matter.

Planting salt sensitive plants uphill or on berms where salty water will not drain or accumulate.

Leaching the soil with thorough irrigation after salt exposure. Flush salt through the soil by applying 2 inches of water over a 2-3 hour period, stopping if runoff occurs. Repeat this treatment three days later if salt levels are still high.

Irrigating thoroughly (deeply) rather than watering lightly (shallow watering). For established landscapes, one inch of water applied once a week is generally adequate.

Mulching to prevent evaporation and subsequent build-up of salt in the soil.

Keeping plants healthy because healthy plants are more tolerant of salt damage.

Selecting and planting salt tolerant trees and shrubs.

Adapted from "Trees and Shrubs that Tolerate Saline Soils and Salt Spray Drift"
Authors: Bonnie Appleton, Extension Specialist; Vickie Greene, Graduate Student; Aileen Smith, Graduate Student; Hampton Roads AREC, Virginia Tech; and Susan French, Virginia Cooperative Extension, Virginia Beach from Virginia Tech Cooperative Extension.

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