Saline Seep Reclamation With Salt-Tolerant Alfalfa
February 5, 2020 | View PDF
Dr. Clair Keene, Williston Research Extension Center Cropping Systems specialist, will be discussing saline seep reclamation with salt-tolerant alfalfa at 3:20 p.m. at the Hard Spring Wheat Show, Williston, ND.
Since June 2016, Dr. Keene has been researching how to prevent saline seep formation and growth. Saline seeps are discharge areas on the soil surface that are caused by salt accumulation at low points in the landscape. When salty groundwater is within six feet of the soil surface, it is pulled to the soil surface, and the water evaporates and leaves behind dissolved salts, which then creates a saline seep. They typically form at the bottom of hills and on the sides of slopes.
Some of the early signs of saline seep development is a flush crop growth combined with high crop yields, increasing moisture (causing inaccessibility), and abundant growth of Kochia and foxtail barley. The later signs are sparse germination of crop plants, declining crop yields, increasing numbers of salt-tolerant weeds, and the formation of salt crystals on the soil surface.
At the Williston Research Center, a saline seep occupies one to two acres of a dryland field. The seep has been around for approximately 20 years but began to increase in size within the last seven years.
Dr. Keene's goal has been to lower the water table to 10 feet below the surface under the seep and hold it there year-round. Keene said, "When a water table is six feet or less below the surface, capillary action and evaporation allows salty groundwater to get pulled up and bring the salts with it. The water evaporates but the salts remain. That is why salty ground gets saltier over time if you don't manage the water table.
Dr. Keene has sampled forage production from the four alfalfa varieties: AFX 457, PGI 427, Rugged and Magnum Salt. "They all seem to have decent salt tolerance, but I do caution that our soil was not extremely salty, to begin with. In terms of hay production, AFX 457 and Rugged were the highest in 2017, PGI 427 and Rugged were the highest in 2018, and in 2019 PGI 427 and Magnum Salt were the highest. We've also sampled the electrical conductivity (EC) in the top 0-3" of the soil each fall. With EC values, the higher the number, the saltier soil is, so lower numbers are good, that is less salty. An EC value less than 2.0 is considered non-saline. From this sampling, we've seen that we've reduced the average EC of our seep from 2.2 dS/m in 2016 to 0.9 dS/m in 2019."
"Seeing that we can flush salts down out of the top three inches in just four years is very exciting. That means that the alfalfa is doing its job lowering the water table, which is allowing the salts to get flushed down with snowmelt and rainfall."
In years to come, Keene will continue monitoring forage production, water table level, and soil EC in 2020. She said, "After that, we're not sure if we'll keep the perennials or go back to annual crops in 2021. We know the annual crops will raise the water table and counteract the good work of the perennials, but we're curious to know how quickly that happens. We will probably leave some of the alfalfa in to help manage the wet slough on the east side of the field. That area is almost always too wet to plant, so leaving it in perennials and not getting the tractor stuck seems like the best plan to me!"
For landowners who deal a lot with saline seeps, Keene suggests growing perennials to manage the water table. "Perennials should be planted on the ground that is contributing to the high water table. This is typically up-slope of the seep. The point is that if you want to stop losing ground to salt, you have to manage more than just the seep itself, you've got to manage the water table that is contributing to the seep. If you don't want to plant alfalfa or salt-tolerant perennial grasses, then look at growing more high water, use cash crops like sunflower, millet, or sorghum-sudangrass as an annual forage. The problem isn't going to get better until you start managing the water table," explained Keene.
To learn more about managing saline seeps and Keene's research, you are welcome to attend the Hard Spring Wheat Show, Williston, ND, on Feb. 13.