Sodium toxicity in plants

Impact of Road Salt on Adjacent Vegetation

It’s the first day of spring… Consider that roadside vegetation has been exposed to de-icing compounds following several recent late-winter storms. Runoff from treated pavement contains dissolved salts that can injure adjacent vegetation. In plants sensitive to excessive salt, affected foliage may scorch and drop prematurely. In severe cases, the death of twigs, branches, and sometimes the entire plant, may occur.

Why is road salt used?

Salts (usually chloride-based) are applied to roadways, driveways, and sidewalks to melt the ice and snow, enhancing safety for motorists and pedestrians. These compounds are usually applied before (anti-icing) or during (de-icing) storms where precipitation is expected to accumulate. The salt dissolves in water to form a brine that has a freezing point lower than water. The brine melts the ice and helps to prevent the formation of more ice as temperatures drop. To improve traction, de-icing salts are often mixed with abrasives such as sand, cinders, gravel, and sawdust.

Anti-icing products are applied before accumulation is expected. Applied most often in liquid form, anti-icers prevent the bonding of ice to the roadway. De-icing products, usually applied as solids, break existing bonds between ice and the pavement and are most often used when plows are needed to clear roadways. In New Jersey, the most commonly applied deicers are rock salt (sodium chloride), liquid calcium, and salt-water brine solutions. To keep the approximately 13,000 lane miles of interstate and state highways clear of precipitation, The New Jersey Department of Transportation stores up to 164,000 tons of rock salt, 720,000 gallons of liquid calcium chloride, and 150,000 gallons of salt brine.

How does road salt affect vegetation?

Plants become injured when roots and foliage are exposed to salt-laden water. The foliage on roadside vegetation is damaged when salted water sprays up from the pavement by passing vehicles. Salt-laden water can also percolate down through the soil profile, coming into contact with soil particles, soil microbes, and plant roots. Salt injures vegetation by:

• Increasing water stress. In the root zone, water molecules are held very tightly by salt ions, making it difficult for roots to absorb sufficient quantities of water. In sensitive species, this “physiological drought” may result in depressed growth and yield.

• Affecting soil quality. The sodium ion component in rock salt becomes attached to soil particles and displaces soil elements such as potassium and phosphorus. As a result, soil density and compaction increases and drainage and aeration are reduced. In addition, chloride and calcium can mobilize heavy metals in affected soils. Plant growth and vigor are poor under these conditions.

• Affecting mineral nutrition. When the concentration of both the sodium and chloride components of salt in the root zone is excessive, plants preferentially absorb these ions instead of nutrients such as potassium and phosphorus. When this occurs, plants may suffer from potassium and phosphorus deficiency.

• Accumulating to toxic levels within plants. The chloride component of salt is absorbed by roots and foliage and becomes concentrated in actively growing tissue. Plants repeatedly exposed to salt over long periods of time may accumulate chloride ions to toxic levels, resulting in leaf burn and twig die-back.

How do plants respond to excessive salt?

Unlike animals, plants do not have mechanisms to excrete excess salt from tissues and can only “shed” salt in dead leaves and needles. Because conifers do not shed leaves on a yearly basis, they tend to suffer damage from accumulated salt more easily than do deciduous trees.

Plant species vary in their tolerance to salt exposure (see plant species listings below). Plants that are tolerant of salt grow as well in saline soils as they do under normal conditions. Many herbaceous plants such as grasses adapt fairly readily to high salt levels. Among woody plants, tolerance varies with the species. Plant species with waxy foliage or scaled, protected buds are generally more tolerant of salt spray.

In salt-sensitive plants, exposure to salt can result in poor growth, stunted leaves, heavy seed loads, twig and branch die-back, leaf scorch, and premature leaf drop. Plants stressed by excessive salt are also more susceptible to biotic diseases and insect pests. The extent of injury a plant sustains in response to salt depends on:

• The kind and amount of salt applied. Sodium chloride (rock salt) can be very damaging to plants. De-icing compounds without chloride, such as urea, are safer for vegetation.

• The volume of fresh water applied. Although salts are easily leached by water in well-drained soils, they tend to accumulate in poorly-drained soils, so the potential for damage to vegetation in these soils is high. High volumes of water, whether from rainfall or melting snow, will decrease the possibility of injury. Rainfall also washes salt from foliage surfaces.

• The distance plants are situated from treated pavements. Plants within the “spray zone” of moving vehicles (about 15 feet, and more if down wind) are more likely to sustain salt injury. Injury is usually most evident on the side of the plant that faces the highway.

• The direction of surface-water flow. The channeling of drainage water away from susceptible plants will prevent salt from coming into contact with plant roots. Plants situated up-slope or away from drainage areas are less likely to be affected.

• The time of year salt is applied. Salt applied in late winter and early spring is more likely to damage vegetation than salt applied earlier in the winter season. This is because there is less time for winter snow and precipitation to leach salt from the root zone before growth resumes in the spring.

How can we minimize salt injury?

The best solution to the de-icing salt problem is to prevent contamination. On sidewalks and driveways, clear the snow first, and then use minimal de-icing product to treat the pavement. If vegetation is located in areas where salt spray occurs, erect barriers or screens to protect plants during the winter months. Anti-desiccants may also help prevent injury when applied to evergreen foliage where de-icing salt will be used. County, state, and municipal officials can help prevent salt injury by carefully training equipment operators and frequently calibrating equipment.

Once soil becomes contaminated with salt, the damage can be reduced by leaching the salt with fresh water as soon as possible after exposure. Under certain circumstances, incorporation of gypsum at the rate of 50 lb/1000 sq ft into the top six inches of soil at the drip-line of trees may also be helpful. Furthermore, foliage exposed to salt spray may be washed with salt-free water to remove deposited salt.

When landscaping, place trees and shrubs that are salt-sensitive as far as possible from problem areas. Select planting sites that are not subject to salt-contaminated waters, and place shallow diversion ditches between roadways and plantings. When vegetation must be placed near roadways, utilize salt-tolerant plants. Keep in mind that stress due to de-icing compounds may predispose plants to diseases and insects and may enhance their sensitivity to other environmental stresses.

Salinity tolerance of selected trees and shrubs.

Note: These listings were compiled from several sources (below). Sensitivity to salt depends on plant species, stage of growth, and environmental conditions. Note that in many cases, tolerance or sensitivity of host plants to salts is based on anecdotal information or studies where responses to soil salinity or salt spray were assessed. Note also that different sources may report different tolerances for the same species.

Moderately tolerant to tolerant trees and shrubs

  • Acer platanoides (Norway maple)
  • Aesculus hippocastanum (Horse-chestnut)
  • Ailanthus altissima (Tree of heaven)
  • Baccharis halimifolia (Eastern baccharis)
  • Betula sp. (, Gray birch, Paper birch, Yellow birch, Sweet birch)
  • Cryptomeria japonica (Japanese cryptomeria)
  • x Cupressocyparis leylandii (Leyland cypress)
  • Elaeagnus angustifolia (Russian olive)
  • Euonymus japonicus (Japanese spindle)
  • Fraxinus americana (White ash)
  • Gleditsia triacanthos (Honeylocust)
  • Ilex sp. (American holly, Inkberry, Yaupon holly)
  • Juniperus sp. (Chinese juniper, Common juniper)
  • Lonicera tatarica (Tatarian honeysuckle)
  • Picea pungens (Colorado blue spruce)
  • Pinus sp. (Austrian pine, Japanese black pine, Mugo pine)
  • Populus sp. (Eastern cottonwood, White poplar)
  • Pyrus calleryana (Callery pear)
  • Quercus sp. (English oak, Red oak, White oak, Willow oak)
  • Robinia pseudoacacia (Black locust)
  • Salix sp. (Weeping willow, White willow)
  • Spiraea x vanhouttei (Vanhoutte spirea)
  • Syringa reticulata (Japanese tree lilac)
  • Syringa vulgaris (Common lilac)
  • Taxodium distichum (Bald cypress)
  • Thuja occidentalis (Arborvitae)
  • Ulmus sp. (Chinese elm, Siberian elm)
  • Zelkova serrata (Japanese zelkova)

Sensitive trees and shrubs

  • Abies sp. (Balsam fir, Concolor fir)
  • Acer negundo (Boxelder)*
  • Acer sp. (Black maple, Red maple, Silver maple)
  • Aesculus glabra (Ohio buckeye)
  • Albizia julibrissin (Silktree)
  • Alnus sp. (European alder, Gray alder, Hazel alder)
  • Amelanchier sp. (Serviceberry)
  • Asimina triloba (Pawpaw)
  • Berberis thunbergii (Japanese barberry)
  • Betula sp. (Bog Birch, European white birch, River birch)
  • Buxus sempervirens (Common boxwood)
  • Carpinus sp. (American hornbeam, European hornbeam)
  • Carya sp. (Bitternut hickory, Pignut hickory, Shagbark hickory)
  • Ceanothus americanus (New Jersey tea)
  • Cedrus atlantica (Atlas cedar, Blue atlas cedar)
  • Celtis occidentalis (Common hackberry)
  • Cercidiphyllum japonicum (Katsura tree)
  • Cercis canadensis (Eastern redbud)*
  • Chaenomeles japonica (Japanese flowering quince)
  • Chamaecyparis sp. (Altantic white cedar, Sawara)
  • Cornus sp. (Cornelian cherry, Flowering dogwood, Redosier, Tatarian dogwood)
  • Corylus sp. (American filbert, European filbert)
  • Cotoneaster sp. (Cotoneaster)
  • Crataegus crus-galli (Cockspur hawthorn)*
  • Cytisus scoparius (Scotch broom)
  • Elaeagnus umbellata (Autumn elaeagnus)*
  • Euonymus alatus (Winged euonymus)
  • Fagus sp. (American beech, European beech)
  • Forsythia suspensa (Weeping forsythia)
  • Fraxinus nigra (Black ash)
  • Fraxinus pennsylvanica (Green ash)**
  • Gaultheria sp. (Creeping snowberry, Eastern teaberry)
  • Gaylussacia sp. (Black huckleberry, Blue huckleberry, Dwarf huckleberry)
  • Gingko biloba (Gingko)*
  • Hamamelis virginiana (American witchhazel)
  • Hypericum sp. (St. Johnswort)
  • Ilex cornuta (Chinese holly)*
  • Ilex sp. (Burford holly, Common winterberry, Japanese holly)
  • Juglans sp. (Butternut, Eastern black walnut)
  • Juniperus virginiana (Red cedar)*
  • Kalmia latifolia (Mountain laurel)
  • Lagerstroemia indica (Crape myrtle)
  • Larix decidua (European larch)*
  • Larix laricina (Tamarack)
  • Ligustrum amurense (Amur privet)*
  • Liquidambar styraciflua (American sweetgum)*
  • Liriodendron tulipifera (Tuliptree)
  • Lonicera maackii (Amur honeysuckle)
  • Maclura pomifera (Osage orange)
  • Magnolia sp. (Cucumber-tree, Sweetbay, Umbrella-tree)
  • Mahonia aquifolium (Oregon grapeholly)
  • Malus sp. (Crabapple)*
  • Metasequoia sp. (Redwood)
  • Morus alba (Common mulberry)*
  • Morus rubra (Red mulberry)
  • Nyssa biflora (Swamp tupelo)
  • Nyssa sylvatica (Black tupelo, black gum)*
  • Ostrya virginiana (American hophornbeam)
  • Paulownia tomentosa (Princess tree)
  • Physocarpus opulifolius (Common ninebark)
  • Picea sp. (Black spruce, Norway spruce, Red spruce, White spruce)
  • Pinus sp. (Eastern white pine, Loblolly pine, Red pine, Scots pine, Shortleaf pine, Virginia pine)
  • Platanus occidentalis (Planetree)
  • Prunus sp. (American plum, Black cherry, Cherry plum, Chickasaw plum, Kwanzan cherry, Sand cherry)
  • Pseudotsuga menziesii (Douglas fir)
  • Pyrus communis (Common pear)
  • Quercus sp. (Black oak, Chestnut oak, Chinkapin oak, Pin oak, Post oak, Scarlet oak, Shingle oak, Southern red oak, Swamp chestnut oak, Swamp white oak, Water oak, Willow oak)
  • Quercus macrocarpa (Bur oak)**
  • Rhododendron sp. (Azalea, Rhododendron)
  • Rhus copalinum (Winged sumac)
  • Rosa sp. (Rose)
  • Salix sp. (Coastal plain willow, Golden weeping willow, Laurel willow, Pussy willow, Sageleaf willow, Sandbar willow)
  • Sambucus canadensis (American elder)
  • Styphnolobium japonicum (syn. Sophora japonica) (Japanese pagodatree, Scholar-tree)*
  • Sassafras albidum (Sassafras)
  • Sorbus americana (American mountain ash)
  • Spiraea sp. (Steeplebush, White meadowsweet, White spirea)
  • Taxus sp. (Yew)
  • Taxus canadensis (Canadian yew)
  • Tilia sp. (American basswood, Basswood, Littleleaf linden)
  • Tsuga canadensis (Canadian hemlock, Eastern hemlock)
  • Ulmus sp. (American elm, Chinese elm, Rock elm, Slippery elm)
  • Vaccinium sp. (Blueberry, Deerberry)
  • Viburnum sp. (Blackhaw, Cranberrybush, Mapleleaf viburnum, Nannyberry)

*Sensitive to moderate tolerance depending on source.

**Sensitive to high tolerance depending on source.

Sources:

  • Sinclair, W., and Lyon, H. 2005. Diseases of Trees and Shrubs, 2nd. Comstock/Cornell University Press.
  • Urban Horticulture Institute. 2009. Recommended Urban Trees: Site Assessment and Tree Selection for Stress Tolerance. Department of Horticulture, Cornell University.
  • Miyamoto, S., Martinez, I., Padilla, M., Portillo, A., and Ornelas, D. 2004. Landscape Plant Lists for Salt Tolerance Assessment. Texas A&M University Agricultural Research and Extension Center at El Paso, Texas Agricultural Experiment Station.
  • Woody plants database, Cornell University: http://woodyplants.cals.cornell.edu/
  • USDA PLANTS database: http://plants.usda.gov/java/

Physiological traits of sodium toxicity and salt tolerance

Abstract

Worldwide up to 20 % of the irrigated arable land is already salt-affected; that portion is still expanding. The decline in crop productivity in salt-affected soils is caused by several factors, including salt-induced mineral perturbations in plants, e.g. K + and Ca 2+ deficiencies. The salt-induced growth inhibition is especially pronounced in leaves as compared to roots. It is well known that salinity causes toxic symptoms, especially in older leaves after long-term exposure. In addition, a relationship has been shown between high Na + concentrations in older leaves and the death of those leaves. Therefore, Na + accumulation in leaves, particularly in the leaf apoplast, could be responsible for Na+ toxicity in corn leaves. Furthermore, lower Na + concentrations in leaves of a more salt tolerant corn cultivar were found as compared to higher Na + concentrations in a salt sensitive corn cultivar. Thus, it is also of interest if the more tolerant corn cultivar exhibits a lower Na + concentration in the leaf apoplast under salt stress. In this context, more salt tolerant (cotton) and salt sensitive crops (rice) were also used in order to compare the results with corn. Mineral ion analyses were carried out in the apoplast, symplast and in whole leaves after salt treatment. The determination of Na +, K + and Ca 2+ in the leaves was carried out by ion chromatography. In addition, Na + sensitive fluorescent dyes were used to detect the Na + concentration in the leaf apoplast by in vivo fluorescence ratio imaging. The Na + concentration in the leaf apoplast of a salt sensitive corn cultivar (Pioneer 3751) significantly increased with higher Na + supply. In contrast, a lower apoplastic Na + concentration was found in leaves of a more salt tolerant corn cultivar (Pioneer 3769). In comparison to corn, higher Na + concentrations were found in leaves of more salt tolerant cotton during salinity, whereas similar low Na+ concentrations were found in the leaf apoplast of salt sensitive rice plants. Nevertheless, the apoplastic Na + concentrations did not exceed about 20 mM at a NaCl concentration of 150 mM in the medium. Therefore, the Na+ concentration in the leaf apoplast was not high enough to be responsible for the decline in leaf growth. The K + and Ca 2+ concentrations in whole leaves decreased with salt treatment, while K + increased and Ca 2+ remained constant in the leaf apoplast under salt stress.

Salinity Management Guide

Leaves of plum trees damaged by sodium

Toxicity of specific ions — A brief introduction

The total salinity of irrigation water is an important consideration for any landscape project. If water containing too much salt is applied during irrigation, salt tends to build up in the soil, reducing the amount of water available to plants.

Individual ionic constituents are also an important consideration. Three constituents, in particular, have considerable potential to damage or otherwise adversely affect ornamental plants: sodium ion (Na+) , chloride ion (Cl-), and boron (B).

Sodium ion

The roots of a plant can absorb sodium ion and transport it to the plant’s leaves. From there, the sodium has nowhere else to go and typically accumulates. For some species, this accumulation of sodium causes no obvious symptoms. For others, especially such woody plants as azaleas, camellias, roses, and stone fruits, necrosis of leaves is a common result. Typically, this manifests as marginal scorching of the leaves or abscission (dropping) of the leaves.

Many species of plants also absorb sodium directly through their leaves, from water present on the leaves (resulting either from rainfall or from sprinkled irrigation water). If a plant absorbs more sodium by this pathway than it can tolerate, abscission of leaves is a common result.

Leaves of plum tree damaged by chloride

Chloride ion

Plants can absorb chloride via their roots and store it in their leaves. When this happens, depending on the plant’s sensitivity to chloride, toxic symptoms may appear. Those symptoms are similar to the ones seen when sodium becomes a problem: scorching or abscission of leaves. Foliar absorption of chloride is also common. It may, for sensitive plants, result in the abscission of leaves.

Boron

Boron is quite toxic to many plants, even at low concentrations. As little as 0.8 mg/L can result in leaf margin necrosis.

Plants absorb boron through their roots and store it in their leaves. Boron is not normally absorbed directly via the leaves, however. Consequently, irrigating a boron-sensitive plant with sprinklers is no more hazardous to the plant than are furrow irrigation, drip irrigation, or other methods that tend not to spray or mist water onto the plant’s leaves.

Boron-damaged (spotted) eucalyptus leaves

Specific ions in recycled water

Recycled water typically has higher concentrations of sodium ion, chloride, and boron than the water from which it was made. This is especially true when the recycled water originates from a community where many houses have been equipped with salt-based water softeners and where residents frequently use cleansers containing boron.

Prior to irrigating a landscape with recycled water, it’s wise to determine or estimate the concentrations of sodium ion, chloride, and boron in the water. Very low concentrations of sodium, chloride, and boron actually can be beneficial, because they help plants to grow. When those concentrations are exceeded, however, sodium ion, chloride, and boron can become a problem for plants, as outlined in the foregoing paragraphs.

Some types of plants can tolerate higher concentrations of sodium, chloride, and boron than others. For instance, trees and shrubs, which are longer-lived than herbaceous plants, have more time in which to accumulate ions and thus tend to be more severely affected than annual plants. As another example, consider turf grasses. Most of them tolerate high Na+ levels and much higher Cl- levels. Boron tolerance is relatively good, too, compared to other types of plants.

Chemical tolerances vary by plant species as well as by plant type. That is why it is vital to know the particular tolerances of plants being irrigated.

The Impact of Salts on Plants and How to Reduce Plant Injury from Winter Salt Applications

Across the country, more than 22 million tons of road salt is used every year. In Massachusetts, the Department of Transportation (MassDOT) recommends one or more applications of salt at 240 lbs per lane mile after every snow fall to ensure the safety of those using the roadways.

The most commonly used salt for deicing roads is sodium chloride (rock salt) because it is inexpensive, effective and readily available. Despite the benefits of improving safety on roads, streets, sidewalks, driveways and parking lots, deicing salt can cause damage to landscape plants. Deicing salts can cause injury and contribute to the decline and death of landscape plants. However, an understanding of the impacts salts have on plants and salt application management strategies can help to protect plants or reduce plant injury due to salt.

How Salt Affects Plants

Salt damage occurs on plants when salt is deposited by spray from passing cars on stems and buds of deciduous woody plants and on stems, buds, leaves and needles of evergreen plants. Salt spray can cause salt burn on buds, leaves and small twigs. Salt spray can also cause damage by desiccating the bud scales, exposing tender tissues of the developing leaves and flowers. The unprotected developing leaves and flower buds dry out and are often killed by the cold winter wind. Many times, the damage is not evident until late winter or spring. Needle or leaf browning, bud death, and branch dieback on the side of the plant facing the road or sidewalk is a common sign of salt spray damage. Damage to deciduous plants is not seen until growth resumes in the spring.

Plants are also affected by dissolved salts in runoff water. Sodium and chloride ions separate when salts are dissolved in water. The dissolved sodium and chloride ions, in high concentrations, can displace other mineral nutrients in the soil. Plants then absorb the chlorine and sodium instead of needed plant nutrients such as potassium and phosphorus, leading to deficiencies. The chloride ions can be transported to the leaves where they interfere with photosynthesis and chlorophyll production. Chloride accumulation can reach toxic levels, causing leaf burn and die-back.

Rock salt also causes damage when salt laden snow is plowed or shoveled onto lawns and garden beds. Salts in the soil can absorb water. This results in less water being available for uptake by the plants, increasing water stress and root dehydration. This is referred to as physiological drought, which, if not corrected, can lead to reduced plant growth.

The displacement of other mineral nutrients by sodium ions can also affect soil quality. Compaction can increase while drainage and aeration decrease, generally resulting in reduced plant growth. Damage from salt in the soil can be delayed, with plant symptoms not appearing until summer or even years later. Symptoms may also become evident during periods of hot, dry weather.

The extent of damage can vary with plant type, type of salt, fresh water availability and volume, movement of runoff, and when salts are applied. De-icing salts without sodium are safer for plants than sodium chloride. Salts applied in late winter generally result in more damage than salts applied in early winter because there is a better chance the salt is leached away before active root growth in spring. The volume of fresh water applied to soils also impacts the amount of salts leached away, while rainfall can wash salt from leaves.

Common Symptoms of Salt Injury

  • Damage mostly on the side of the plant facing the road or sidewalk
  • Browning or discoloration of needles beginning at tips
  • Bud damage or death
  • Twig and stem dieback
  • Delayed bud break
  • Reduced or distorted leaf or stem growth
  • Witches’ broom development (tufted and stunted appearance)
  • Wilting during hot, dry conditions
  • Reduced plant vigor
  • Flower and fruit development delayed and/or smaller than normal
  • Fewer and/or smaller leaves than normal
  • Needle tip burn and marginal leaf burn
  • Discolored foliage
  • Nutrient deficiencies
  • Early leaf drop or premature fall color

Management Strategies for Mitigating Salt Injury

Reduce salt use. Combine salt with other materials such as sand, sawdust, or cinders that can provide grittiness for traction. De-icing materials that use salts other than sodium chloride, including calcium chloride, magnesium chloride, potassium chloride, or calcium magnesium acetate (CMA) are more expensive but can reduce injury to plants.

Make applications carefully. Applications should be targeted at walkways and roadways, not landscape beds or lawns. The flow of salt-laden runoff water should be considered for when snow melts. Avoid planting in areas where runoff naturally flows. Leaching soils by watering heavily can help remove salts from well-drained soils. This is not possible with poorly draining soils. Improve drainage of poorly drained soils by adding organic matter. To determine if you have high salt buildup in the soil, send a soil sample to the UMass Soil and Plant Nutrient Testing Laboratory.

Protect plants with physical barriers such as burlap, plastic, or wood. Use salt tolerant plants in areas near roads, driveways, and sidewalks. Remember that salt tolerant does not mean injury free.

The following is a table of the reported salt tolerance of selected trees and shrubs. It is important to keep in mind when choosing plants considered “salt tolerant” that the degree of tolerance and extent of damage are dependent on many factors, with tolerance varying in plants within the same species. Tolerance can also vary depending on method of salt exposure (spray vs. soil). There are conflicting reports for salt tolerance of many species. Soil type and climate variability can result in differences in plant response between areas.

Tolerant – Intermediate Tolerance

Type of Salt Tolerance

Deciduous Trees and Shrubs

Acer campestre

hedge maple

Spray

Aesculus hippocastanum

horsechestnut

Spray and soil

Betula papyrifera

paper birch

Spray

Gleditsia triacanthos var. inermis

thornless honeylocust

Spray and soil

Larix spp.

larch

Spray

Quercus alba

white oak

Soil

Quercus rubra

Northern red oak

Spray and soil

Rhus spp.

sumac

Spray and soil

Rosa rugosa

rugosa rose

Spray and soil

Ulmus hybrids

elm hybrids

Spray and soil

Evergreen Trees and Shrubs

Juniper spp.

juniper

Spray and soil

Picea glauca

white spruce

Spray and soil

Picea pungens/Picea pungens ‘Glauca’

Colorado spruce/ Colorado blue spruce

Spray and soil

Pinus mugo

Mugo pine

Spray and soil

Sensitive Plants

Acer rubrum

red maple

Acer saccharum

sugar maple

Amelanchier spp.

serviceberry

Buxus sempervirens

common boxwood

Cornus sericea

red twig dogwood

Juglans nigra

black walnut

Picea abies

Norway spruce

Pinus strobus

Eastern white pine

Pseudotsuga menziesii

Douglas fir

Quercus palustris

pin oak

Tilia cordata

littleleaf linden

Tsuga canadensis

Eastern hemlock

Viburnum spp.

viburnum

The following sources also have lists of reported salt tolerance of some common landscape plants:

Soluble Salts in Soils and Plant Health

Literature Cited:

Beckerman, J. and B.R. Lerner. 2009. Salt Damage in Landscape Plants. Purdue Extension. Factsheet ID-412-W

Gould, Ann. 2013. Impact of Road Salt on Adjacent Vegetation. Rutgers Cooperative Extension. New Jersey Agricultural Experiment Station.

Hunter, G. 1980. Salt Injury to Roadside Plants. Cornell University Bulletin 169.

Johnson, G.R. and E. Sucoff. 1999. Minimizing de-icing salt injury to trees. University of Minnesota Extension.

MassDOT Highway Division. 2015. Winter Road treatment and snow removal

Smithsonian.com. January 6, 2014. What happens to all the salt we dump on the roads?

Sodium Tolerance Of Plants – What Are The Effects Of Sodium In Plants?

Soil provides sodium in plants. There is a natural accumulation of sodium in soil from fertilizers, pesticides, run off from shallow salt-laden waters and the breakdown of minerals which release salt. Excess sodium in soil gets taken up by plant roots and can cause serious vitality problems in your garden. Let’s learn more about sodium in plants.

What is Sodium?

The first question you need to answer is, what is sodium? Sodium is a mineral that is generally not needed in plants. A few varieties of plants need sodium to help concentrate carbon dioxide, but most plants use only a trace amount to promote metabolism.

So where does all the salt come from? Sodium is found in many minerals and is released when they break down over time. The majority of sodium pockets in soil are from concentrated runoff of pesticides, fertilizers and other soil amendments. Fossil salt runoff is another cause of high salt content in soils. The sodium tolerance of plants is also tested in coastal areas with naturally salty ambient moisture and leaching from shorelines.

Effects of Sodium

The effects of sodium in plants are similar to those of exposure to drought. It’s important to note the sodium tolerance of your plants, especially if you live where groundwater run-off is high or in coastal regions where ocean spray drifts of salt to plants.

The problem with excess salt in soil is the effects of sodium on plants. Too much salt can cause toxicity but more importantly it reacts on plant tissues just as it does on ours. It produces an effect called osmotion, which causes important water in plant tissues to be diverted. Just as in our bodies, the effect causes tissues to dry out. In plants it can impair their ability to even uptake adequate moisture.

Buildup of sodium in plants causes toxic levels that cause stunted growth and arrested cell development. Sodium in soil is measured by extracting the water in a laboratory, but you can just watch your plant for wilting and reduced growth. In areas prone to dryness and high concentrations of limestone, these signs are likely to indicate a high salt concentration in soil.

Improving Sodium Tolerance of Plants

Sodium in soil that is not at toxic levels can easily be leached out by flushing the soil with fresh water. This requires applying more water than the plant needs so the excess water leaches away the salt from the root zone.

Another method is called artificial drainage and is combined with leaching. This gives the excess salt laden water a drainage area where water can collect and be disposed of.

In commercial crops, farmers also use a method called managed accumulation. They create pits and drainage areas that funnel salty waters away from tender plant roots. The use of salt tolerant plants is also helpful in managing salty soils. They will gradually uptake sodium and absorb it.

Critical Reviews in Plant Sciences

Plant scientists usually classify plant mineral nutrients based on the concept of “essentiality” defined by Arnon and Stout as those elements necessary to complete the life cycle of a plant. Certain other elements such as Na have a ubiquitous presence in soils and waters and are widely taken up and utilized by plants, but are not considered as plant nutrients because they do not meet the strict definition of “essentiality.” Sodium has a very specific function in the concentration of carbon dioxide in a limited number of C4 plants and thus is essential to these plants, but this in itself is insufficient to generalize that Na is essential for higher plants. The unique set of roles that Na can play in plant metabolism suggests that the basic concept of what comprises a plant nutrient should be reexamined. We contend that the class of plant mineral nutrients should be comprised not only of those elements necessary for completing the life cycle, but also those elements which promote maximal biomass yield and/or which reduce the requirement (critical level) of an essential element. We suggest that nutrients functioning in this latter manner should be termed “functional nutrients.” Thus plant mineral nutrients would be comprised of two major groups, “essential nutrients” and “functional nutrients.” We present an array of evidence and arguments to support the classification of Na as a “functional nutrient,” including its requirement for maximal biomass growth for many plants and its demonstrated ability to replace K in a number of ways, such as being an osmoticium for cell enlargement and as an accompanying cation for long-distance transport. Although in this paper we have only attempted to make the case for Na being a “functional nutrient,” other elements such as Si and Se may also confirm to the proposed category of “functional nutrients.”

In animals, Sodium (Na) is an “Essential” element. It plays a central role in electrolyte and ion balance in body fluids and tissues. In plants however, Na is the most predominating problem salt and can cause toxicity. We often consider it a waste product that is pervasive in our soils and waters. While Na may not be necessary to completing the life cycle of a plant; i.e. “Essential” nutrient,” it can increase growth rates, yields and reduce Potassium (K) critical level needs. Scientists have labeled elements like Na as “Functional” nutrients. “Functional” nutrients are those which are crucial to maximizing yield or in reducing critical levels of an “Essential” nutrient like Potassium (K) by partially replacing it.

Na is a “Functional” nutrient.

Typically our mental reference to Na in plant nutrition and culture is toxicity, necrosis, tip burn, chlorosis, scorching, bronzing and even death. It is something we are taught to avoid if at all possible at any level or concentration. Most of us have been taught no Na is the goal, but in fact, this is not the case at all. While plant species vary widely in Na uptake and translocation capabilities, what we usually read or hear about is plants subjected to very high Na concentrations in the root zone. There it is translocated to the tops which reduces growth and can cause death. However at proper levels, Na plays some major beneficial roles in plant metabolism including:

  • Chlorophyll synthesis
  • Turgor pressure, osmotic potential and cell expansion
  • Reducing critical levels of K
  • Stomatal function
  • Nutrient transport
  • Enzyme activation
  • Growth stimulation

The processes listed above are beyond the scope of this blog. Suffice it to say Na function and metabolism in the plant is vast and still largely unresolved. Na is not an “Essential” element, but it is a “Functional” one. In fact, Na is an “Essential” element in some C4 plant species like corn and sugar cane. That is, it is required to complete the life cycle. None the less, much research indicates Na significantly stimulates growth in many plant species, even when K is adequate. Research also indicates K critical levels are reduced in the presence of Na in many crops. Growth rate and nutrient utilization and efficiency are positively affected by Na.

Whether it is increased chlorophyll production in spinach or lettuce, or increased tomato yields, or improved taste in carrots or sweetness in watermelons and citrus, or higher yields in broccoli, cotton, barley, carrots and many other crops, Na is not the bad guy. It is a “Functional” nutrient. It is an element that can increase yield, increase quality and increase disease resistance in some species.

The point of this blog is to help the reader understand there is more to plant nutrition and culture than N, P & K. Plants require a balanced diet of not only the “Essential” nutrients but also the “Functional” ones. These nutrients are required in varying amounts. It is a dynamic system with elements interacting with each other, the water, the soil and the plant species in production. Na can be extremely beneficial to plant quality, characteristics and performance. Who would have thought Na could be a good guy?

Address your nutritional program needs on a species specific basis. Know your beginning nutrient levels, water quality and characteristics. Use complete plant foods and fertilizers that not only consider the “Essential” nutrients but also the “Functional” ones.

At BGI, species specific complete balanced and available nutrient plant foods is our design. It’s what we do. Why do we do It? We believe that without beauty life would be intolerable. That beauty is as necessary as sunlight and oxygen to our health and survival. We believe beauty is a divine presence and an “Essential” element to human existence. BGI believes in creating or helping to create beauty in all aspects of our lives, be it in the natural landscape or on the harshest edges of our existence. Why? Because beauty is the ultimate food…soul food! I’m starving!

Take care,

Tom

P.S. If you don’t agree with this blog, go pound Salt

All waters used to irrigate, be they recycled or otherwise, contain in dissolved form various compounds of salt — the familiar sodium chloride and others, such as sodium sulfate, magnesium sulfate, and calcium carbonate.

Salt exists in water as ions. Up to a certain amount of the ions can be helpful to plants. During absorption and transpiration of water, plants obtain some of the ions they need to survive and grow.

Recycled water typically contains more of some nutrients, such as nitrogen, phosphorus, and potassium, than the water from which it originated. As a result, irrigating with recycled water often lessens the need to add fertilizers containing these nutrients.

Chemical elements that plants need

Element Role
Nitrogen Helps plants to produce new, green growth
Phosphorus Promotes growth of roots
Potassium Contributes to overall hardiness, helping plants to resist extreme temperatures, pests, and diseases
Sulfur Helps plants to produce protein and maintain their dark green color
Calcium Helps plants to produce protein, promotes growth of roots, and contributes to overall vigor
Magnesium Helps plants to use light to make food, to absorb other nutrients, and to make seeds
Iron Helps plants to photosynthesize and to form chlorophyll
Manganese Helps plants to form chlorophyll and to conduct essential cellular functions
Chloride Helps plants to metabolize
Boron, cobalt, copper, zinc Help plants with certain natural processes, such as absorbing nutrients, growing new tissue, metabolizing, and forming chlorophyll

Beyond that nutritional amount, less is more. The less salt present in the water used to irrigate, the more likely the water will not harm plants.

When the salt in irrigation water accumulates to excess, one or more of the following scenarios may ensue:

  • The osmotic effect induced by a relatively high amount of salt may adversely affect less-salt-tolerant plants.
  • Excessive concentrations of certain ions may adversely affect less-tolerant plants.
  • An excessive accumulation of sodium in the soil may alter the soil, rendering it less able to sustain plants.

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