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First: identify the source of salt.
Management depends heavily on whether salt is coming from tidal inundation, saline groundwater, or both. Reducing salt accumulation is different from trying to restore a soil that has already accumulated Na and other salts. Preventing salts from entering coastal soils is likely difficult, but should be examined as an option.
Drainage and water movement
Good drainage can help remove soluble salts when fresh water is available for leaching. However, drainage is complicated in low-lying coastal fields because of water tables are typically located close to the surface. Drainage systems (tile or ditches) can also provide pathways for tidal water to move inland. Simply installing or improving drainage should not be assumed to solve a saltwater problem. One method to assist with drainage and salinity is a tide gate, which allows water to flow out, but prevents saline water from easily entering the ditch.
Saturated soils on a sunny day imply a high water table during tidal events along a wetland boundary. [photo: Jarrod Miller]
A tide gate situated along a drainage ditch should help prevent saline waters from flowing into the field (overland at least). [photo: Jarrod Miller]
Leaching with fresh water
Soluble salts can be moved below the root zone when sufficient fresh water passes through the soil. Annual rainfall can typically achieve this result on Delmarva, at least out of the root zone. This is a fundamental approach to reducing salinity, but its usefulness on Delmarva will depend on soil texture, depth to groundwater, drainage, elevation, and continued exposure to saltwater. Leaching cannot provide a lasting solution if salt continues to enter the field.
Using Soil Amendments for Salinity and Sodicity
Most research in soil amendments comes from arid climates, and research under Delmarva conditions is lacking. Soil amendments are used to reduce the negative effects of salts on plant growth as well as encourage the leaching of Na from the soil. For salinity, the addition of organic materials in the form of manure, compost, or biochar have shown positive effects on plant growth. However, this has not been examined under conditions where salts come from brackish waters. Where Na has accumulated on the soil exchange sites, management becomes more complicated. Calcium amendments such as gypsum are commonly used to help replace exchangeable sodium, but the displaced Ns still needs to be moved out of the root zone with water. Gypsum should therefore not be viewed as a treatment for salinity itself, and its effectiveness will depend on the soil and drainage conditions. See recommendations: Amendment Applications
Crop selection and field management
Where salt concentrations are too high for a current crop, changing the crop or using more salt-tolerant crops may allow continued production in affected areas. However, crop tolerance varies considerably, and tolerance to salinity does not necessarily mean tolerance to prolonged flooding or poor drainage. See more: Crop Selection
Sorghum is more tolerant to drought and salinity than corn or soybean.
Multiple stressors exist in these fields
Salinity is not the only factor that may cause reduced crop productivity in these fields. Herbivory by deer and birds is common in these fields, reducing vegetative growth and grain harvest. Salinity causes drought to be more intense as well, and flooding will also frequently reduce crop growth. Flooding will depend on timing, and should occur during the growing season to cause issues.
A field bordering tidal sources being converted into a conservation easement where crop growth became too marginal.
Know when remediation may not be practical
Some fields may receive salt frequently enough, or remain wet enough, that maintaining conventional crop production becomes increasingly difficult. In those areas, long-term decisions may involve changing land use, establishing vegetation better suited to the site, or considering conservation or other land-management options
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