What effect does sodium chloride from a water softener have on plants?
Answer: Salts are naturally found in soils and are essential to all plants and animals. Most soils naturally contain low salt levels and can provide plants with an adequate supply of nutrients necessary for plant growth. The salts are in a form that can be taken up by plants. However, an accumulation of salts in the soil can cause plant growth problems, including “burning,” and also make it difficult for plants to take up and retain water. In addition to being used as a water softener, sodium chloride is used agriculturally as a fertilizer and an herbicide and also to manage plant diseases. The amount of salt content varies in the way it is used. Looking at its application rates is one way to understand its effects on plants. In small amounts–approximately one part salt per 1,000 parts soil–salt can promote plant growth. However, at greater levels–around one pound of salt per gallon of water–the salt acts as an herbicide. Excessive use of salt-containing fertilizers or herbicides, as well as irrigating with high levels of salt in the water, can cause soil issues, including soil crusting. Normal levels of salt in the soil are below 1 millimhos per centimeter (mmho/cm). As mentioned, small amounts of salt can provide plant nutrients necessary for plant growth. This depends on the type of salt, the soil type, and the crops being grown. Temperate soils usually have enough natural salt needed for plant growth, so the addition of salt is unnecessary. Sodium chloride is used in water conditioners because the sodium replaces the calcium and magnesium in “hard” water. The amount of sodium contained within softened water is extremely low and plants are not normally affected by the sodium. Other salts sources that contain potassium, nitrogen, calcium, and magnesium tend to make better plant fertilizers. Potassium chloride can be used instead of sodium chloride as a water softener and can be beneficial as potash source. There are several brands of potassium chloride that do not contain sodium, and an Internet search is a good way to learn about them. Agricultural soils that contain high levels of salts need to have the salts removed from the root zones. This can be done through leaching and implementing artificial drainage as there are no chemical means for removing soils. Crop selection is also important to consider for saline soils as crops vary in their tolerance to salt. For example, beets, kale, asparagus, and spinach have a high salt tolerance while radishes, celery, and beans have a low salt tolerance. The following crops tend to fall in the medium range (between 4 mmhos and 10 mmhos): tomato, broccoli, cabbage, pepper, cauliflower, lettuce, corn, potato, carrot, onion, pea, squash, and cucumber.No matter what type of water conditioner you are using, you should check the salt content in the soil routinely. Most soil-testing laboratories, such as land grant universities, can test for salt content. The ATTRA website offers a directory of Alternative Soil Testing Laboratories at http://www.attra.org/attra-pub/soil-lab.html.There are many great resources available to learn about soil micronutrients. The ATTRA website is a great place to start, as we have several publications that focus on soil nutrients. In addition, each publication and section on the ATTRA website contains a list of further resources.