Farm Progress

Both stunt growth of many crops and reduce yields, but they have to be managed differently

June 27, 2018

4 Min Read
SOIL LESSON: NDSU Extension soil health specialist Chris Augustin explains what is happening in the soil at this demonstration pit.NDSU

There two types of salt-impaired soils — sodic and saline soils. They are closely related and often have common symptoms. But they aren’t the same thing and require different management to correct. You need a soil test determine which is which.

1. Saline soils have excessive levels of soluble salt (NaCl) in the soil water. The levels can get high enough to negatively affect plant growth, resulting in reduced crop yields and even kill the plants completely. The primary effect of excessive soluble salts on plants is to limit the ability of plant roots to absorb soil water even under wet soil conditions. Drought-like symptoms are common.

2. Sodic soils have excessive levels of sodium (Na+) absorbed at the cation exchange sites in the clay particles. Soil sodicity causes degradation of soil structure and the sealing off of the soil pores so that roots and water can’t penetrate.

Both are caused by the sodium rich bedrock in the Northern Plains and a high water table.

Saline soil management
For saline soils, Naeem Kalwar, soil health specialist at NDSU’s Langdon Research Extension Center, recommends trying to get a mix of salt-tolerant perennial grasses such as tall wheatgrass, slender wheatgrass, green wheatgrass (AC Saltlander) and Russian wildrye to grow. Seeding rates will be 7-8 pounds per acre and will cost about $30-$35 per acre. They take about a year to establish and about two years to suppress weeds. "The goal is to get something established there, some kind of vegetative cover," he says. "These grasses will grow where nothing else will grow."

Cover crops are a good option, too. Some species are frost tolerant and will use water earlier and later in the season than most grasses and crops.

You can also try to intercept water coming into the problem area. In-field and boundary-field ditches can improve soil drainage and facilitate leaching of salts.

Installing surface or subsurface tile systems may improve drainage. A thorough analysis of soil properties should be done before installing any subsurface drainage system, though. Excessive leaching of calcium and magnesium can lead to the sealing of soil layers, either around or above the tiles.

"Salinity can be reduced," says Chris Augustin, Extension soil health specialist at NDSU’s North Central Research Extension Center, Minot. "It comes down to water management. It’s up to you if you choose to manage the water with cropping systems or drainage, but both methods are effective."

Sodic soil management
In order to reclaim sodic soils, you first have to replace the excessive sodium from the caption exchange site in the soil with a large amount of calcium. Common amendments are calcium sulfate and calcium chloride on alkaline soils, and calcium carbonate on acidic soils. Like saline soils, sodic soils also require good soil drainage and low groundwater level. The only difference between management sodic soil is the application of calcium supplements and thoroughly mixing it into the soils. Once sodium is displaced by calcium at the cation exchange sites, sodium converts to a salt and can be leached out of the root zone.

Saline-sodic soil management
Management of salinity and sodicity are more complicated when both occur in the same soil together. A saline-sodic soil normally does not exhibit strong sodicity symptoms. However, as the soil salinity decreases through improved drainage or management, calcium and magnesium salts are leached away and sodium is more slowly leached and eventually dominates the soil. Reclamation of saline-sodic soils is like management of sodic soils. You need to apply a calcium soil amendment and then take steps to improve soil drainage and lower the water table, Augustin says.

Always first step
The first step in any case is to do a thorough job of soil sampling to determine the location, degree, type and extent of a soil problem, says Dwayne Beck, a South Dakota State University agronomist manager of the Dakota Lakes Research Farm, Pierre, S.D.

Using a Web Soil Survey to identify the soil types and topography of the field will be helpful. Obtain help from NRCS or your state extension service in interpreting the results.

"It is important to determine why the problem is occurring before trying to find a solution. One thing is certain, adding more salts [gypsum or other amendments] to a soil that is already impacted by salt is not the correct approach," he says. "You need to figure out what is going on before trying to solve it. It’s also important to act quickly.

"The thing about managing salinity is it’s a lot like planting a tree," Kalwar says. "The best day to do it was yesterday. If you don’t manage your salinity today, it’ll be worse tomorrow."

Sources: NDSU and SDSU Extension Service

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