The winter season in Ohio ultimately means some degree of snowfall and an ample application of salt and brine solutions to streets and sidewalks. A 2011 report by the Ohio Department of Transportation (ODOT) indicates they service 43,000 lane miles of road every year with an average salt application of 600,000 tons (1). Additionally, private companies and homeowners apply ice-melting compounds in anticipation of snow and ice. While thankful for safe roads to drive on, car enthusiasts bemoan the corrosive properties of the anti-ice compounds that accumulate on their vehicles. Salty, sloppy roads do not just turn your favorite car into a rust-bucket, however. An additional, less obvious outcome to road salt application is the impact it can have on surrounding vegetation.

An article by Ann Gould of the Rutgers Cooperative Extension describes how the sodium and chloride ions in runoff water can damage plants by causing burns on leaf material, killing buds, or creating a toxic accumulation in plant cells over a period of time (2). The extent of damage really depends on the type of plant; grasses are among the more resistant and woody plants are typically more susceptible. This makes sense as the long strips of grass bordering our highways get covered with salty spray from passing cars and heavy runoff, yet cope very well with minimal care. 

Salt tolerance in grass has been noted for some time. One study dating back to the late 1920s describes some South African grasses that were successfully grown in highly saline soils created by faulty agricultural irrigation practices, and ultimately provided ample grazing material on the previously barren plot of land (3). Likewise, the susceptibility of woody plants to salt damage was carefully documented early on. One such study, published in 1929 by researchers at the University of California, examined the effects of watering walnut trees with a saline solution over a period of four years. Ultimately, these trees suffered from smaller root and shoot masses, as well as leaf burning and reduced calcium content compared to the control trees (4).

The consequences of salt in the soil go beyond inflicting physical damage to plants. In an article from the Crops and Soils magazine, Madeline Fisher writes that the singly-charged sodium ions promote dispersion of soil clay particles, whereas ions with higher charge cause particles to stick together (5). For this reason, gypsum - or calcium sulfate dihydrate - is a common additive to saline soils as the doubly-charged calcium ions improve soil structure, thereby reducing erosion and water logging (2, 5).

A lot of salt is not always a problem, however. Sodium bentonite, perhaps the most extreme case of salty soil, has some really amazing and useful properties. In this type of soil, sodium ions are so saturated amongst clay particles that  it can swell up to 18 times its dry mass when watered (6). At this point, it makes a great sealant due to its low permeability, and is often employed as a natural landfill liner (6). 

Over time as interest increased in converting arid regions with saline soils to cultivatable lands, the research output on plants increased in kind. Just this year, over 80 articles have been published that discuss everything from gene expression, metabolomics, and pathogenicity factors relating to salt stress and/or tolerance in tomato, Arabidopsis, rice, and various other plants. There is even an entire Gordon Research Conference called "Salt and Water Stress in Plants" dedicated to the topic every two years (7). Clearly, this simple two-element compound can have some very complicated consequences, and will no doubt be a favorite topic in the plant sciences for years to come. 

Find more information here:
(1) Ohio Department of Transportation
(2) Rutgers Cooperative Extension. 
(3) Smith, C. A., and C. E. Hubbard. "Notes on African Grasses, IX. Some Saline-Loving Grasses Occurring in South Africa." Bulletin of Miscellaneous Information (Royal Botanic Gardens, Kew), vol. 1929, no.3, 1929, pp. 83-87.
(4) Haas, A. R. C. "Composition of Walnut Trees as Affected by Certain Salts." Botanical Gazette, vol. 87, no. 3, 1929, pp. 364-396.
(5) Amending Soils with Gypsum
(6) STURGIS
(7) Gordon Research Conferences
 

Written by TPS Fellow, Irene Gentzel