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How to Manage Soil Salinity
With site-specific management, those white spots in your fields that show high soil salinity might be reclaimed.
“Soil salinity is caused by excess soil moisture that dissolves subsoil salts and brings those salts to the soil surface,” says Chris Augustin, Extension soil health specialist at North Dakota State University’s North Central Research Extension Center. “The water evaporates, and the salts are left. They accumulate and cause the white spots that limit plant growth.”
Taking stock of the landscape is the first step in reclamation. The spots in fields that are crusted in white typically show places where water is pooling. As the water evaporates, the salts remain and accumulate.
“These areas tend to expand,” says Augustin.
Rising water tables tend to cause salinity problems over a more generalized area. “As the water table moves up, the water evaporates, but the salts don’t,” he says. “They leave white spots in the field.”
Dry weather and open winters worsen the problem. “When snow melts, it leaches the salts downward,” says Augustin. “If there is no leaching, the salts move up to the surface.”
Tillage also makes matters worse. While tilling the saline area temporarily darkens the soil, the tillage speeds up evaporation, worsening the soil’s problem with salinity over the long term.
Managing soil water is the key to reducing salt content in the soil. Augustin suggests the following six strategies.
1. Test soil for electrical conductance (EC).
Salt raises the EC.
2. Make a site-specific management plan.
Test for EC in zones radiating out from the bull’s-eye of the problem area, where the soil is crusted with white. Plant species of crops or forages with the salt tolerance to adapt to various zones. Choosing deep-rooted species will help to manage soil water.
3. Plant salt-tolerant perennial grasses in the bull’s-eye.
In areas where the EC tests 8 or higher, try planting for hay or forage species such as tall wheatgrass, western wheatgrass, beardless wild rye, NewHy hybrid wheatgrass, or Garrison creeping foxtail.
4. Choose salt-tolerant crops.
In the zone radiating out from the bull’s-eye (where the soil EC tests more than 2), plant salt-tolerant cash crops such as barley, sunflowers, or canola. “Corn and soybeans are poor choices because they’re not salt-tolerant,” says Augustin.
5. Plant a salt-tolerant cover crop.
The beauty of planting barley in relatively high-saline areas is that its late-July or early-August harvest affords a window of opportunity for planting a salt-tolerant cover crop. During the months of August, September, and October, the cover crop uses soil moisture that would otherwise evaporate and accumulate more salts on the surface.
One option is a per-acre cover crop mix of 25 pounds of barley, 5 pounds of sunflowers, and 2 pounds of sugar beets. “These crops winterkill,” says Augustin. “Because the plants are young when they freeze over, the residue has a lot of nitrogen in it, causing the residue to decompose quickly.”
6. Plant salt-tolerant alfalfa.
“As you get farther out from the bull’s-eye (where the EC tests 4 or 5), you might try one of the varieties of alfalfa selected for salt tolerance,” says Augustin. “Because alfalfa is deep rooted, it uses a lot of moisture.”
Reclamation of saline areas can take five to 10 years, with periodic monitoring and management modifications needed to minimize salts in the soil.
“By making some management changes, you can improve saline areas and have an opportunity for growing a successful crop,” says Augustin.