Chloride (Cl-)

Chloride is the most recent addition to the list of essential elements. Many people make the common mistake of confusing the plant nutrient chloride (Cl-), with the toxic form chlorine (Cl). Chlorine is not the form that plants use. Chlorine exists either as a gas, or dissolved in water, such as bleach, and is not found in fertilizer. Although Chloride is classified as a micronutrient, plants may take-up as much Chloride as secondary elements such as Sulfur.

Function

Chloride is essential for many plant functions. Some of them are

Factors Affecting Availability

Most soil Cl is highly soluble and is found predominantly dissolved in the soil water. Chloride is found in the soil as the Chloride anion. Being an anion it is fully mobile except where held by soil anion exchange sites (Kaolinite clays, Iron and Aluminum Oxides). 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, boron, and molybdenum 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.

High Response Crops

Alfalfa, broccoli, brussel sprouts, cabbage, cauliflower, lettuce, oil palm, potato, small grains, sugar/table beets, and tomatoes.

Deficiency Symptoms

Wilting, restricted and highly branched root system, often with stubby tips. Leaf mottling and leaflet blade tip wilting with chlorosis has also been observed. Chloride insufficiency in cabbage is marked by an absence of the cabbage odor from the plant.

Toxicity Symptoms

Toxic symptoms are similar as is found with typical salt damage. 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 symptoms are a yellow mottling of the needles, followed by the death of the affected needles.

Chloride Tolerance of Agricultural Crops

(Listed in order of increasing tolerance)

Crop

Maximum Soil Cl- Conc.* Without Yield Loss (threshold ppm)

Percent Yield Decrease

per ppm Cl- Conc. Increase Above Threshold

Strawberry

350

0.094

Bean

350

0.054

Onion

350

0.046

Carrot

350

0.04

Radish

350

0.037

Lettuce

350

0.037

Turnip

350

0.026

Rice, paddy **

1050

0.034

Pepper

525

0.04

Clover, strawberry

525

0.034

Clover, red

525

0.034

Clover, alsike

525

0.034

Clover, ladino

525

0.034

Corn

525

0.034

Flax

525

0.034

Potato

525

0.034

Sweet potato

525

0.031

Broadbean

525

0.028

Cabbage

525

0.028

Foxtail, meadow

525

0.028

Celery

525

0.017

Clover, Berseem

525

0.017

Orchardgrass

525

0.017

Sugarcane

525

0.017

Trefoil, big

700

0.054

Lovegrass

700

0.023

Spinach

700

0.023

Alfalfa

700

0.02

Sesbania **

700

0.02

Cucumber

875

0.037

Tomato

875

0.028

Broccoli

875

0.026

Squash, scallop

1050

0.046

Vetch, common

1050

0.031

Wildrye, beardless

1050

0.017

Sudangrass

1050

0.011

Wheatgrass, standard crested

1225

0.011

Beet, red **

1400

0.026

Fescue, tall

1400

0.014

Squash, zucchini

1575

0.026

Hardinggrass

1575

0.023

Cowpea

1750

0.034

Trefoil, narrow-leaf birdsfoot

1750

0.028

Ryegrass, perennial

1925

0.023

Wheat, Durum

1925

0.014

Barley (forage) **

2100

0.02

Wheat **

2100

0.02

Sorghum

2450

0.046

Bermudagrass

2450

0.017

Sugarbeet **

2450

0.017

wheatgrass, fairway crested

2625

0.02

Cotton

2625

0.014

Wheatgrass, tall

2625

0.011

Barley **

2800

0.014

Note: These data serve only as a guideline to relative tolerances among crops. Absolute tolerances vary depending upon climate, soil conditions, and cultural practices.

* Cl- concentrations in saturated-soil extracts sampled in the rootzone.

** Less tolerant during emergence and seedling stage.

Values for paddy rice refer to the Cl- concentration in the soil water during the flooded growing conditions.

Taken from Chloride and Crop Production, Special Bulletin No. 2, Potash & Phosphate Institute

Using Chloride in a Fertility Program

Some Common Fertilizer Products Containing Chloride:

Material

Formula

Percent Cl

Sodium Chloride

NaCl

61%

Potassium Chloride

KCl

47%

Calcium Chloride

CaCl2

64%

Soil and Plant Analyses do not routinely include Chloride analyses but, most laboratories are able to accomplish the assessment. Although interpretative data are 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 is occurring.

In areas where deficiencies are known to exist, 30 to 100 lb./Acre of Chloride per year will supply the needs of responsive crops. Response may be improved if the application is split. For example 30 lb./A fall applied Cl- and 70-80 lb./A spring applied can improve wheat yields over single applications.