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As you might expect, we are receiving questions from county agents, landscapers, and property owners about saltwater flooding effects on soils and plants and the appropriate remediation. The information below may be helpful in answering these questions. (Thanks to Stephanie Murphy for pulling together a lot of this information).
Problems from Saltwater
There are a number of potential problems caused by saltwater including: i) the direct effect of burn (osmotic stress) on plant tissue; ii) dehydration of plants (physiological drought stress) caused by increased osmotic potential in soil; iii) plant damaged by sodium (Na) toxicity; iv) loss of soil structure caused by excessive Na; and v) soil infertility caused by increased soil pH (excessive alkalinity).
Testing for Soluble Salts and Sodium
Soluble salts and pH are the basic soil tests needed to begin the assessment for long term soil problems related to saltwater flooding. Soil testing for “soluble salts” by electrical conductivity (EC) is a special test (typically not included with a standard fertility test) with modest additional fee of $10 at the Rutgers Soil Testing Laboratory. Test of soil pH is part of the standard soil fertility test. Evaluation of the Na level in soil can also be determined by an evaluation of exchangeable cations (with or without evaluation of cation exchange capacity). The lab’s soil test reports include a brief interpretive statement along with the data. A document on the Soil Testing website has interpretations of EC values and related information: http://njaes.rutgers.edu/soiltestinglab/pdfs/ec-interpret.pdf
What Can/Should You Do about Saltwater Flooding?
The immediate remediation efforts should focus on enhancing drainage and removal of flood water. Longer term, management practices should be implemented to remove residual salts from the soil. This typically involves amending the soil with gypsum (calcium sulfate) and leaching of the salts with fresh water (rain or irrigation). Application of fresh water helps to dilute the residual salts (reducing osmotic stress) in the soil and, as more fresh water is added, to leach the residual salt below the plant’s root zone. For finer-textured soil, it is important to add gypsum before leaching is practiced otherwise the loss of soil structure (due to excess Na) could result in a waterlogged site. Gypsum (calcium) is useful because it helps to displace Na from the soil (exchange sites). Gypsum should be finely ground and well mixed into topsoil for best results. Gypsum is moderately soluble (dissolves slowly), and its solubility is actually enhanced by the presence of Na. Therefore, apply 1 to 2 ton per acre if gypsum can be mixed into the root zone; otherwise make multiple applications of gypsum in smaller amounts before leaching (heavy rain or irrigation) events.
Why is Sodium (Na) a Problem?
Excess sodium is problematic because it destroys soil structure. Excess sodium disperses the small soil particles (colloids), which can then clog soil pores and inhibit drainage and leaching. This may not be a critical factor in the case of many coastal soils (sands, loamy sands) since very sandy soils are “single-grained” and lack the small particles (clay and organic matter) that can be dispersed and clog pores. However, tidal river floodplains (including the inner coastal plain) will have finer textured soils that will be adversely affected by excess Na (inhibit drainage and leaching).
Sulfur
Elemental sulfur (S) is an effective alternative to gypsum in calcareous (high pH) soils/sands such as those with high shell (calcium carbonate) content. Sulfur is converted (by bacteria in soil) into sulfuric acid which reacts with shells (calcium carbonate) to produce calcium. The calcium is then available to help displace and leach sodium from the soil, which improves soil permeability and reduces the hazards of sodium. Sulfur amendment is not as widely available as gypsum, so you may have to make a special request from a supplier should you need to treat a calcareous soil.
Salinity Tolerance
You should expect damage to cool season grasses that were inundated by saltwater flooding. Of the most common turfgrasses grown in New Jersey, annual bluegrass, rough bluegrass, colonial bentgrass, some Kentucky bluegrasses, and some creeping bentgrasses will be the most sensitive to salinity. Most fine fescue species as well as some Kentucky bluegrasses and some creeping bentgrasses are thought to be moderately tolerant of salinity. Perennial ryegrass, slender creeping red fescue, and tall fescue are generally considered to have the best tolerance to salinity of the cool season turfgrasses that are commonly grown in our region.
If you need to assess whether the turf is dead or dormant, you can simply remove a core or spade full of sod (turf and soil) from the site of interest and place it in a planting pot or pan containing some good (not salt-affected) potting mix. Place the replanted sod sample in a warm (65 to 75 degrees F) sunny location and water. Water to leach excess salts out of the soil and potting mix; you may want to lightly sprinkle gypsum over the sod before watering. New leaves should start to regrow from the damage piece of sod within a week or so if the plants have not died.
Other Reading
Below are two publications from Extension at Colorado State University that describe saline and sodic soil conditions. Keep in mind that the publications were written from the perspective of saline and/or sodic soils due to an arid climate rather than from saltwater flooding.
http://www.ext.colostate.edu/pubs/crops/00503.html
http://www.ext.colostate.edu/pubs/crops/00504.html
Here are some eXtension resources that describe soil salinity and sodic problems.
http://www.extension.org/pages/62292/soil-salinity
http://www.extension.org/pages/63502/solutions-to-soil-problems:-high-salinity
http://www.extension.org/sites/default/files/w/1/1e/Salinitydocument.pdf
North Carolina has a publication about salt tolerant ornamental species, for those needing to replant!
http://pender.ces.ncsu.edu/files/library/71/Salt%20Tolerant%20Plants.pdf