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
- It is essential (working in tandem with K+) to the proper function of the plants stomatal openings, thus controlling internal water balance.
- It also functions in photosynthesis, specifically the water splitting system.
- It functions in cation balance and transport within the plant.
- Research has demonstrated that Cl diminishes the effects of fungal infections in an, as yet undefined, way.
- It is speculated that Cl competes with nitrate uptake tending to promote the use of ammonium N. This may be a factor in its role in disease suppression, since high plant nitrates have been associated with disease severity.
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. 1) 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 2) | 1050 3) | 0.034 4) |
| 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 5) | 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 6) | 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) 7) | 2100 | 0.02 |
| Wheat 8) | 2100 | 0.02 |
| Sorghum | 2450 | 0.046 |
| Bermudagrass | 2450 | 0.017 |
| Sugarbeet 9) | 2450 | 0.017 |
| wheatgrass, fairway crested | 2625 | 0.02 |
| Cotton | 2625 | 0.014 |
| Wheatgrass, tall | 2625 | 0.011 |
| Barley 10) | 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. 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.