New Life for Saline Soil

Those dead zones in fields where crops fizzle out and give way to kochia and foxtail barley are places where perennial grasses might lend a hand. Research suggests these may actually reclaim soil from excess salinity.

At North Dakota State University's Carrington Research Extension Center, research specialist Ezra Aberle has for six years evaluated perennial grasses, legumes, and cover crops for their performance in soils of varying salinity. His research included:

• 35 species of cover crops
• 12 varieties of alfalfa
• 3 species of other legumes
• 11 perennial grasses

Plantings were evaluated under both conventional-till and no-till management. Some species of cover crops were grown under no-till stabilized soil salinity.

"However, with the perennial grasses," says Aberle, "I've been able to lower the soil salinity. This suggests it could be possible to achieve remediation over time."

Testing for electrical conductance (EC) indicates the salinity level – or salt content – in soil. "Soil that has an EC rating of 4 or higher is considered saline, even though such soil may not show the telltale whiteness typically associated with soil salinity," says Aberle. "Those white areas in fields may actually have EC readings of 6 to 30."

While saline soil with an EC of 4 may not appear white, the salinity is likely to show up in decreased crop performance.

"The salt in the soil works like a drought," he says. "The salt holds water so tightly that plants can't pull it away. The water is there, but plants can't use it, so yields decrease."

When water isn't used, soil salinity worsens because the moisture evaporates from the surface, leaving salt behind.

"Excess soil salinity is a water-management issue," says Aberle. "Fields and areas within fields that are problematic probably had ECs of 3 and 4 before being farmed. Farming practices combined with the long-term wet cycle we've had since the 1990s, however, have caused ECs in some areas to climb into the 8 to 20 range or higher. Saline areas are getting bigger and bigger, and part of that has to do with the growing of crops that don't tolerate salinity. These crops don't use the water, and so it comes to the surface and evaporates. The key is to use the water before it gets to the surface."

A strategy for managing soil water centers on matching crop types to EC levels. Aberle suggests a three-pronged approach.

1. Plant cash crops that tolerate salt.

With an EC level of about 4 or lower, soil salinity can be stabilized by growing cash crops adapted to moderate soil salinity.

"The most salt-tolerant crops are barley, camelina, rye, safflower, sunflower, and sugar beets," says Aberle. "We've replaced a lot of these crops with the least-tolerant crops, which are dry beans, soybeans, corn, and field peas."

2. Grow cover crops that are salt tolerant.

Aberle evaluated 35 species of cover crops grown in areas with ECs of 6.5 or lower. He managed the cover crop plantings as if they qualified for prevent-plant provisions by federal crop insurance standards.

Aberle seeded the full-season cover crops in June and July as high soil moisture receded enough to allow equipment into saline areas. Cover crop species with reasonable seed costs that performed best were rape, barley, rye, Siberian millet, and sorghum-Sudan grass.

"By planting cover crops, I was able to maintain soil EC, but salinity didn't improve," he says. "The only way I was able to lower EC was by growing grass and alfalfa."

3. Plant perennial grasses in the worst saline areas.

"When EC is above 6.5 or 7, consider growing alfalfa and perennial grasses in these areas," says Aberle. "These plants tolerate higher levels of salinity."

Twelve varieties of alfalfa were included in Aberle's research; 11 of these were salt-tolerant. "The salt-tolerant varieties do have better germination in saline conditions, but seed costs are significantly higher," he says.

When trying to reclaim high-saline soils, he suggests growing saline-tolerant alfalfa above the rim of the white area in a strip 40 to 60 feet wide. "Beyond that, you should get acceptable performance from a variety of alfalfa you like with a more moderate seed cost," he says.

The growth of wild foxtail barley and kochia in areas with a whitened soil surface suggests that certain perennial grasses may survive there, as well.

"For livestock producers with field areas that are highly saline, I recommend planting AC Saltlander green wheatgrass or NewHy hybrid wheatgrass," says Aberle. "These varieties produce well in saline soil and yield good-quality forage. If you're just looking to plant a grass to use moisture and produce good ground cover, plant any of the tall wheatgrasses, like slender wheatgrass, western wheatgrass, or Canada wild rye. These produce lower quality forage, but they also have lower seed costs."

The perennial grasses are sod forming and, thus, tend to creep into the deepest areas of saline seeps. As grasses get started, their use of soil water lowers the EC in adjacent areas, where the perennials are then able to take hold.

"Over time, the wheatgrasses can choke out foxtail barley," says Aberle.

While Garrison creeping foxtail, a domestic grass species adapted to wet soils, has previously been billed as a good fit for saline areas, Aberle's research finds it less tolerant of salt than some other grass species.

After six years of growing salt-tolerant perennials, saline areas showed improvements in soil ECs, with levels declining from 7 to 10 to 4 to 8.

Total reclamation of saline soil is a long-term process. "It took decades for some soils to become excessively saline," says Aberle. "It'll take many years to restore soil to its more natural state."

Give Grass a Good Start

To start salt-tolerant perennial grasses in saline areas, North Dakota State University researcher Ezra Aberle seeded the grasses into saline areas at the end of June, after soil dried enough to permit passage of equipment. Before seeding, he rolled the tilled fields to create a firm seedbed.

The seeding depth was about ½ inch, and the seeding rate was 8 to 12 pounds per acre. Seed costs came to about $70 per acre.

"I tried to plant just prior to a rain, so the seed would have water to germinate," says Aberle. "The first year, I cut the growth with a rotary mower three or four times to control weeds. In each of the next five years, I cut the grass for hay."