Chlorine effect on plants

The Functions of Chloride
Factors Affecting Chloride Availability
Chloride Deficiency Symptoms
Chloride Toxicity Symptoms
Using Chloride in a Fertility Program
Application Information
The Functions of Chloride
Chloride is essential for many plant functions.

The primary roles of chloride include:

  • Chloride is important in the opening and closing of stomata. The role of the chloride anion (Cl-) is essential to chemically balance the potassium ion (K+) concentration that increases in the guard cells during the opening and closing of stomata.
  • Chloride also functions in photosynthesis, specifically in the water splitting system.
  • Chloride functions in cation balance and transport within the plant.
  • Chloride diminishes the effects of fungal infections in an as yet undefined way.
  • Chloride competes with nitrate uptake, tending to promote the use of ammonium nitrogen. Lowering nitrate uptake may be a factor in chloride’s role in disease suppression, since high plant nitrates have been associated with disease severity.

Chloride is a critical component in the development of plants.

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Factors Affecting Chloride Availability
Most soil chloride is highly soluble and is found predominantly dissolved in the soil water. Chloride is found in the soil as the chloride ion. Being an anion, it is fully mobile except where held by soil anion exchange sites. In areas where rainfall is relatively high and internal soil drainage is good, it may be leached from the soil profile. Also, where muriate of potash fertilizer is not regularly applied, chloride deficiencies can occur. Atmospheric chloride deposition tends to be rather high along coastal regions and decreases as you progress inland.
Chloride, nitrate, sulfate, borate, and molybdate are all anions in their available forms, and in that form they are antagonistic to each other. Therefore, an excess of one can decrease the availability of another. Little information is available on other specific interactions that may occur.

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Chloride Deficiency Symptoms
Too little chloride in plants can cause a variety of symptoms.

Chloride deficiency symptoms include:

  • Wilting due to a restricted and highly branched root system, often with stubby tips, and
  • Leaf mottling and leaflet blade tip wilting with chlorosis has also been observed.

In particular, chloride deficiency in cabbage is marked by an absence of the cabbage odor from the plant.

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Chloride Toxicity Symptoms
Too much chloride in plants results in symptoms that are similar to typical cases of salt damage.

Chloride toxicity symptoms include:

  • Leaf margins are scorched and abscission is excessive.
  • Leaf/leaflet size is reduced and may appear to be thickened.
  • Overall plant growth is reduced. Chloride accumulation is higher in older tissue than in newly matured leaves. In conifers, the early symptom is a yellow mottling of the needles, followed by the death of the affected needles.

Identifying toxicity in plants can help avoid long term damage.

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Using Chloride in a Fertility Program
Soil and plant analyses do not routinely include chloride analyses, but most laboratories are able to assay for chloride. Although interpretative data is limited, soil and plant analyses can be useful, especially where specific questions arise. Be aware that insufficiencies do not usually exist where muriate of potash fertilizer is routinely used or in saltwater coastal areas where atmospheric deposition naturally occurs. Hi-Cal™ fertilizer from TETRA is an excellent source of chloride for plants.

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Application Information
In areas where deficiencies are known to exist, 30 to 100 pounds per acre of chloride per year will supply the needs of responsive crops. Response may be improved even further if the application is split. For example, apply 30 pounds per acre of chloride in the fall and 70 to 80 pounds per acre in the spring.

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Chlorine

Chlorine Toxicity

Chlorine toxicity can occur naturally when plants are grow in coastal soils and near chlorinated pools (though much of the damage associated with chlorinated pools is due to the vapours coming into contact with leaves rather than because the plant has uptake too much chlorine).

Symptoms of Chlorine Toxicity

Chlorine toxicity will usually result in necrosis along leaf margins and smaller than usual leaves and plants. Symptoms are usually seen on older leaves first. In some species, chlorosis may also occur.

Treating Chlorine Toxicity

As always, your first port of call is the soil pH. You should ensure the pH of your soil is around 7. It’s also a good idea to make sure your soil isn’t compacted and that it drains freely. Plants may struggle to uptake some other from the soil if there is a significant imbalance so it’s a good idea to check that your soil contains adequate amounts of nutrients that form in the soil such as nitrogen, sulfur and phosphorus. Chlorine is easily leached from the soil so temporary chlorine toxicity (perhaps through accidental contamination as a result of excess fertiliser use or a pool chemical spill) may be alleviated through frequent watering. Just be sure to replenish other elements that may also be leached from the soil in this way.

If your soil contains high levels of chlorine because you live on the coast, you may need to grow chlorine tolerant plant species. You could also grow plants in containers and regularly replace the potting mix when chlorine levels rise.

Chlorine Toxicity

Excess Chlorine

Scorched leaves may be the result of chlorine toxicity. Chlorine is a micronutrient, essential to plant growth. However, too much chlorine can accumulate in leaf tissue, resulting in leaves with a scorched or burned appearance. Trees with scorched leaves have brown or dead tissue on the tips, margins, or between the veins of the leaf. Leaf tissue may appear bleached, instead of scorched. Leaves may be smaller than usual. They may yellow and drop early. Chlorine toxicity can result from air pollution, in the form of chlorine gas, or from excess chloride in the soil.

Excess chloride can build up in the soil from swimming pool runoff, irrigation water, or excess soil salts (sodium chloride). Chlorine (Cl) converts to chloride (Cl-) in the soil and is absorbed by plants in this form. Chloride toxicity is most common in irrigated, dry regions, seacoast areas, and near roads frequently treated with salt in the wintertime. Chloride levels can be reduced with the use of gypsum. Incorporate gypsum into the soil at a rate of 58 lbs. per 1000 square feet, in loam soils. Less gypsum is needed in sandy soils, more in heavy clay soils. Water thoroughly to leach toxic levels of chlorine from the soil.

Damage to plants from chlorine gas is less common than damage from other air pollutants, such as sulfur dioxide, fluoride, and ozone. Chlorine gas is a by-product in the manufacture or incineration of glass, plastics, paints, and stains. It is released from refineries or as a result of chemical spills. Reducing air pollution at its source is the best solution to reduce damage to plants and people. Careful watering practices can reduce air pollution damage to plants. Soil should be dry during periods of exposure to air pollutants, followed by thorough watering after exposure. Wetting the leaves of sensitive plants may help to reduce damage during periods of poor air quality. Trees sensitive to chlorine are ash, boxelder, Siberian crabapple, dogwood, horse-chestnut, silver maple, sugar maple, pin oak, sweet gum, and yellow-wood.

Information On Chloride And Plant Growth

One of the most recent additions to the list of micronutrients is chloride. In plants, chloride has been shown to be an important element for growth and health. Though the condition is rare, the effects of too much or too little chloride on garden plants may mimic other, more common problems.

Effects of Chloride in Plants

Chloride in plants comes mostly from rainwater, sea spray, dust, and yes, air pollution. Fertilization and irrigation also contribute to chloride on garden soil.

Chloride is easily dissolved in water and enters the plant through soil and air. It is essential to

the chemical reaction that allows the opening and closing of the plant’s stomata, tiny pores that allow gas and water to be exchanged between the plant and the air around it. Without this exchange, photosynthesis can’t occur. Sufficient chloride on garden plants may inhibit fungal infections.

Chloride deficiency symptoms include wilting due to restricted and highly branched root systems and leaf mottling. Chloride deficiency in members of the cabbage family is easily detected by the lack of cabbage odor, although research has yet to discover why.

Too much chloride on garden plants, such as those grown at poolside, will result in the same symptoms as salt damage: leaf margins may be scorched, leaves will be smaller and thicker and overall plant growth may be reduced.

Chloride Soil Test

Adverse effects of chloride and plant growth are rare because the element is so readily available through a wide variety of sources and excesses are easily leaches away. General analyses rarely contain a chloride soil test as part of the typical panel, but most laboratories can assay for chloride if requested.

CHLORIDE

CHLORIDE – AN ESSENTIAL NUTRIENT OR HARMFUL ELEMENT?

Chloride is an essential micronutrient and all crops require Chloride in small quantities. However, it is often associated with salinity damage and toxicity.

UPTAKE OF CHLORIDE BY PLANTS

Crops differ both in their chloride requirements as well as in their tolerance to chloride toxicity.

Plants take up chloride as Cl- ion from soil solution. It plays some important roles in plants, including in photosynthesis, osmotic adjustment and suppression of plant disease.

However, high concentrations of chloride can cause toxicity problems in crops and reduce the yield. The toxicity results from accumulation of chloride in the leaves.

TOXICITY SYMPTOMS

Common symptoms of chloride toxicity in plants include necrosis of leaf margins and tips, which typically occur in older leaves first. Excessive leaf burn might eventually result in leaf drop.

However, it might be difficult to diagnose chloride toxicity. It is often hard to distinguish whether the toxicity symptom is directly related to chloride or to other elements that are usually absorbed together with it (e.g. Sodium).

Chloride can also cause leaf damage when deposited on leaves in overhead irrigation.

CHLORIDE SUPPLY TO PLANTS

In many cases, more than a sufficient amount of chloride is supplied from the atmosphere and precipitation, as rainwater usually contains a low concentration of Cl. Therefore, chloride might become a limiting factor for plant growth in areas that are far from the sea.

The natural sources of chloride in groundwater include weathering of rocks, atmospheric deposition and precipitation. In coastal, arid and semi-arid areas, the available groundwater is saline.

Since the Chloride is an anion (carries a negative charge) it does not adsorb to soil particles and moves readily with the water in the soil.

Therefore, water quality and irrigation management are the major factors that affect chloride concentrations in soil.

Water of low to medium salinity contains 100-300 mg/liter (=grams/cubic meter) of chloride.

100 mg/liter X 30,000 liter/ha/day X 365 days / 1,000,000 mg/kg = 1095 kg/ha/year.

Chloride is also constituent of some fertilizers. For example the most common fertilizer containing chloride is KCl (muriate of potash), which contains 47% chloride and 53% K.

Fertilizing with 500 kg/ha KCl will result in application of 235 kg/ha of chloride.

Other chloride containing fertilizers include: CaCl2, NH4Cl and MgCl2.

Chloride classification of irrigation water
Chloride (ppm)

Effect on Crops

Below 70

Generally safe for all plants.
70-140 Sensitive plants show injury.
141-350 Moderately tolerant plants show injury.
Above 350 Can cause severe problems.

Susceptibility ranges for crops to foliar injury from saline sprinkler water.

Cl concentration (mg/L) causing foliar injury

Cl concentration

<175

>700

Apricot

Pepper

Alfalfa

Sugarbeet

Plum

Potato

Barley

Sunflower

Tomato

Corn

Sorghum

Low

Medium

High

Excessive

CHLORIDE IN SOIL ANALYSIS

Since chloride does not bind to soil particles, its level in soil is tested in an aqueous soil extract, like the saturated paste, 1:2 extract (1 volume soil to 2 volumes distilled water), 1:5 extract etc.

IRRIGATION MANAGEMENT

Using water that contain chloride requires appropriate practices in order to keep the chloride level in the soil below the threshold level tolerated by the crop. Excess chlorides should be leached below the active root zone.

Water containing chloride concentration of less than 150 mg/l of chloride are safe for most crops, provided that proper irrigation management practices are applied.

SUMMARY

Although chloride is an essential micronutrient it is often overlooked as a plant nutrient.

A positive response to application of fertilizers containing chloride have been reported in different crops in many parts of the world.

Chloride, at high concentrations, might be toxic to many crops and contributes to the overall salinity. Proper irrigation and fertilization management practices should be taken into consideration where the irrigation water contain high concentration of chlorides.

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