Here's a road map for reclaiming saline or sodic soils.
Spring's a time when ranchers are anxious to carry out the planning of winter. Often, this includes trying to establish vegetation on a waste area or barren site that hasn't produced anything but weeds for several years.
Before you start tilling the area, however, take a closer look at what's causing the problem. Perhaps it's too wet to farm. Have you noticed white areas or “slick spots” in the late summer? What weeds are on the site? Have you sampled and analyzed the soil to determine any adverse soil properties retarding plant growth? If one or more of these answers is yes, you may have a saline or sodic soil and the worst treatment would be tilling the area.
Let's discuss why you should not till the area, how you can determine if it's a saline or sodic problem, and if so, how to prepare a seedbed, what species to consider planting based on a soil analysis, how and when to plant and how to manage the site to regain productivity.
Before attempting to revegetate a saline or sodic site, you must determine the severity and type of salt problem. Begin by sampling soil from depths of 0-6, 6-12, 12-24 and 24-36 in. in late summer or early fall, the time of highest surface salt concentrations. Also, take samples from each area defined by a vegetation or soil change.
Depending on the area's size, one composite sample may do, with 2-3 samples from the same area composited into one sample. If the area is more than 10 acres, take two separate samples, i.e., two samples 0-6 in., two samples 6-12 in., etc., from different locations within the area.
Collect at least a cup of soil for each sample depth, then freeze or dry the samples prior to sending them to a soil laboratory. Request a pH (acid/alkalinity measure), EC (electrical conductivity), texture and — if the pH exceeds 8.2 — an ESP (exchangeable sodium percentage) or SAR (sodium adsorption ratio). These analyses will indicate soil properties and dictate which treatments may be necessary, or possible, as well as the most-suited plant species for establishment and survival.
When soils are sampled, the static water table should also be determined. Determining how far the water table is from the ground surface is important because during the growing season, evaporation pulls moisture to the surface from varying depths, depending on soil texture. The water evaporates leaving the salt behind.
Over time, the salts accumulate and become toxic to plant growth. The water-table measurement, along with the soil analysis, helps determine the type of cultural treatments possible and the species that should succeed on the site.
Soil salinity or soil sodocity is a water problem. It could indicate too much water, a high water table (many times compounded by irrigation), an impervious geologic or soil layer causing a “perched” water table, and/or a soil developed from and underlain with saline marine shales.
Saline soils are defined as the concentration of dissolved mineral salts present in water and soil on a unit volume or weight basis. The major solutes comprising dissolved mineral salts are the cations Na+ (sodium), Ca+2 (calcium), Mg+2 (magnesium), and K+ (potassium); and the anions CI-3 (chloride), SO4-2 (sulfate), HCO3-3 (bicarbonate), CO3-2 (carbonate), and NO3- (nitrate).
Salinity is expressed in a number of ways: equivalents per liter (mol/l); milligrams per liter (mg/l), which equates to parts per million (ppm); EC, which is measured in decisiemens per meter (dS/m); or millimhos per centimeter (mmhos/cm). Salinized soils are classified as follows:
Saline EC > 4, ESP < 15, SAR < 13;
Saline-alkaline EC > 4, ESP > 15, SAR > 13;
Alkaline/sodic EC > 4, ESP < 15, SAR < 13.
Sodic soils are characterized by an excess of Na+ ions in relation to calcium and magnesium. For instance, Montana and Wyoming have mostly saline soils with some saline-alkaline and only isolated occurrences of “black alkali” or sodic soils. Sodic soil reclamation requires the addition of amendments and leaching of salts, and will not be covered in this article.
Soil salinity or sodocity is usually a symptom of a problem. Any revegetation on saline or sodic sites may be futile unless contributing problems, such as excess water, are identified. This may involve irrigation management, diverting water away from a swale, or treating a saline seep recharge area (an area contributing excess water), by continuous or flexible cropping of deep-rooted, high water-use perennials such as alfalfa.
If the soil results indicate soil salinity, seedbed preparation is critical to begin reclamation. Site preparation should not be conventional. Whereas a firm weed-free seedbed is ideal, allowing crops if possible, even weeds, to utilize the available soil moisture is necessary to avoid additional salt build-up within the germination zone. Tillage exacerbates the salt problem by bringing additional salt to the surface, destroys surface water infiltration and destroys plants, albeit weeds, that can grow and maintain a lower water table.
The bottom line is that a weed cover crop is a better management tool for reclaiming saline soils than is tilled fallow. Besides, on many saline soils, equipment can't transverse the site until it dries out in the summer.
Use annual weeds like kochia to your advantage. Once the site dries and can support equipment, terminate the “weed” crop with labeled herbicides or clip it to a 4- to 5-in. stubble height during the growing season. In early fall, perennial weeds should be treated with glyphosate to control competition. Fall dormant planting into the weed stubble can be accomplished using a minimum-till drill after Oct. 15 or during a snow-free period in winter.
There are several benefits of having the weed cover in place, including providing a firm seedbed for selected adapted species. Dead or decaying weed litter, roots and stems facilitate water infiltration into the surface and provide micropores for aeration and move salts away from the seed, reducing evaporation next spring and protecting the emerging seedlings from wind and sun desiccation. Successful germination and establishment are strongly correlated to the amount of surface salt diluted by rainfall at the time of germination.
An alternative to using weeds is to plant a saline-tolerant cover crop like barley, then harvest or terminate its growth during the summer. This may be possible on slightly saline areas that are drier and a drill can be used to plant the crop. The same physical advantages apply to the crop stubble as explained earlier.
Only a few forage species are adapted for seeding on saline soils. Table 1 lists the various species and cultivars, their salinity tolerance, limitations and adaptation characteristics.
Selecting species adapted to the water table and salinity levels of the site will facilitate successful establishment and survival. The tendency is to plant a “shotgun” mixture of several species that can sort themselves out on the soil moisture and salinity gradients. Although this may be the easiest method, and may be feasible on a small area, it may be the most expensive because the adapted species that eventually establish will remain and the rest will perish over time.
A better approach is to tailor the species to the site conditions. Use species that fit the site conditions for the best probability of establishment and long-term survival. A 2-3 species mixture is preferred to minimize interspecies competition.
Species compatibility needs to be considered when developing a seed mixture. Some species have very good seedling vigor. These species develop rapidly, often at the expense of the slower-establishing species in the seed mixture. It's recommended that tall wheatgrass be planted by itself, as it will completely dominate a plant stand after 4-5 years.
Slender wheatgrass also develops rapidly, often producing seed heads the establishment year. Although slender wheatgrass establishes quickly, providing cover and stability to the site, this species characteristically begins to deteriorate after 3-4 years and often will give way to the long-lived species in a mix. Slender wheatgrass is an excellent quick cover species to include in a mix. But it should be seeded at a rate of 2 lbs./acre or less to minimize initial interspecies competitiveness and allow the slow-germinating long-lived species time to establish and provide for long-term reclamation.
Both Russian wildrye and tall fescue are slow to develop and don't have aggressive seedlings. If either of these grasses is the desired species, it should be seeded by itself.
There are dry saline sites and wet saline sites depending on the depth of the water table. Obviously, species adapted to these two extremes shouldn't be planted within the same mixture. If gradients of soil salinity and/or soil moisture are present, mixtures can be designed so that each species will dominate in its most favored condition.
A mixture of ‘Garrison’ creeping foxtail, ‘Rosana’ western wheatgrass, and ‘Shoshone’ beardless wildrye will sort out along a wet salinity gradient with Garrison on the wet mildly saline end of the gradient and Shoshone on the most saline end of the gradient. A mixture of Altai wildrye and Shoshone beardless wildrye will sort themselves along a moisture gradient in which Altai wildrye will be on the drier end and Shoshone on the wetter end.
Complicated mixtures are impractical because of interspecific competition and the various salt tolerances of the different species.
If a site has become too wet to traverse with equipment and salinity is low to moderate, Garrison creeping foxtail is suggested. It can be establish by feeding Garrison hay or using Garrison hay as a mulch on the site. This species thrives on such a site and, once established, will tolerate some increase in the soil-salinity level.
Shoshone beardless wildrye and NewHy hybrid wheatgrass can be established in relatively high levels of soil salinity. Both species are able to spread by rhizomes to fill in the stand and spread into adjacent areas with higher salinity where plants were unable to establish from seed.
A variety of forage grasses (Table 2) are commercially available, with the seed supply of the most salt-tolerant species such as beardless wildrye (Shoshone) and hybrid wheatgrass (NewHy) often in short supply.
Obviously, there are many different species and approaches to reclaiming salinized soils. To diagnose the problem, start with visual observation, take soil samples; attempt to correct the water source of the problem using mechanical and chemical weed control (not tillage); select species adapted to the site conditions; fall dormant plant into a stubble, and clip weeds until a stand of grass is established. Since salinization of the site may have taken years, its reclamation may also take a few years. Be patient.
Larry Holzworth is a former USDA plant materials specialist and currently teaches plant science and plant pathology at Montana State University in Bozeman.
|Soil EC (mmhos/cm)||Guidelines for establishment*|
|Species||Variety||Marginal est. level||Limitations||Adaptation characteristics|
| Beardless wildrye |
|Shoshone||24||High seed dormancy (fall dormant planting required). Slow seedling development.||Good wildlife cover; Rhizomitous — will spread into more severe saline sites; productive & palatable to all livestock.|
| Tall wheatgrass |
|Jose, Alkar Largo, Orbit||22||Very competitive in mixtures; unpalatable in mature stages.||Adapted to high water table and well-drained sites. Good wildlife cover. Good for erosion control and snow management. Very productive if properly managed.|
| Hybrid wheatgrass |
(Elytrigia repens × Pseudoroegneria spicata)
|NewHy||22||Some seed dormancy — may require fall planting. Needs 14 in. of rainfall or elevated water table.||Highly palatable in growing season prior to frost; Slightly rhizomitous. Easier to manage than tall wheatgrass.|
| Altai wildrye |
|Prairieland Pearl, Eejay||20||Low seed yield; poor seedling vigor and competitor with weeds and grasses early in life cycle.||Utilizes deep water tables; loam and clay-loam soils; competes well with weeds once established.|
| Slender wheatgrass |
|Pryor||20||Intolerant of prolonged flooding; short-lived. Moderately competitive with other grasses. Limit seeding rate in mixtures to 2 lbs. pure live seed.||Adapts to wide range of soils (sandy loams preferred); excellent emergence and seedling vigor; good cover. Include as quick cover in mixtures.|
| Russian wildrye |
|Bozoisky-Select Bozoisky II||16||Needs to be seeded alone, with row spacing of at least 18 in. Not flood tolerant. Adapted to upland dry saline sites.||Loams and clay loams; high digestibility and retains nutrient value into fall and winter. Competes well with weeds. Tolerant of cold and drought.|
| Tall fescue |
|Kenmont Alta, Fawn||14||Not compatable in a mixture. Good winter hardiness. Endophyte can cause fescue foot.||Wide range of soils and climates; deep rooting; ideal waterway cover; tolerates poorly drained conditions.|
| Western wheatgrass |
|Rosana Rodan||14||Some seed dormancy — fall or early spring planting recommended.||Drought and flood resistant; good for erosion control; winter hardy; prefers heavy clay soils.|
| Barley (hay) |
|Haybet, Horsford Westford Stockford||12||Grain yield will be reduced in saline conditions; cut early for hay. Check for nitrates.||Highest salt tolerance of small grain species; choose hay variety or drought-tolerant grain variety.|
| Hybrid crested whtg |
(Agropyron cristatum × A. desertorum)
|Hycrest, Hycrest II||10||Tolerates only small periods of flood; cannot tolerate high water tables.||Good seedling vigor and drought tolerance; well-drained loams; good for erosion control & early spring pasture.|
| Creeping foxtail |
|Garrison||8||Unable to tolerate drought; fluffy seed difficult to plant, so use coated seed.||Needs high water table; spreads by rhizomes into saline conditions; withstands flood events.|
| Yellow sweetclover |
|Commercial||8||Only a biennial plant; limited salt-tolerance. Competitive in mixtures.||Adapted to wide range of soils and climates; excellent seed producer; soil-improving.|
| Alfalfa |
|Ladak 65, Spredor III, Shaw, Rambler, Cooper, Travois||6||Not as salt-tolerant as most grasses. Seedling has lower salt tolerance than mature plant.||Choose variety that is drought tolerant and long lived, since area may not be disturbed for long period. Deep-rooting varieties like Rambler will help dry out soil profile in recharge areas.|
|*Soil in Montana's saline seeps contain neutral soluble salts, primarily dissolved sodium, calcium, magnesium, sulfate and nitrate. |
Soil salinity is often measured by Electrical Conductivity (EC) with the units of millimhos per centimeter (mmhos/cm) or decisiemens per meter (dS/m).
The units are interchangeable. Saline soil is defined as greater than 4 mmhos/cm. The pH is usually less than 8.5.
Test the soil in the 0-6 inch layer. EC will vary with age of the seep, depth to ground water and seasonally.
Source: Montana Salinity Control Association Fact Sheet. Updated November 2007.
|Scientific name||Common name||Adapted cultivars||Seeds/lbs.||(Pure live seed lbs./acre)|
|Leymus multicaulis||Beardless wildrye||Shoshone||180,000||6|
|Thinopyrum ponticum||Tall wheatgrass||Alkar, Largo, Jose||79,000||10|
|Leymus angustus||Altai wildrye||Prairieland, Pearle, Eejay||80,000||12|
|Elytrigia repens × Pseudoroegneria spicata||Hybrid wheatgrass||NewHy||135,000||8|
|Elymus trachycaulus||Slender wheatgrass||Pryor, Revenue, San Luis||130,000||6|
|Festuca arundinacea||Tall fescue||Kenmont, Fawn, Goar, Alta||240,000||4|
|Psathyrostachys juncea||Russian wildrye||Bozoisky-Select, Bozosky 2, Swift, Mankota, Vinall||170,000||5|
|Pascopyrum smithii||Western wheatgrass||Rosana, Rodan, Walsh||95,000||8|
|Alopecurus arundinaceus||Creeping foxtail||Garrison, Retain||720,000||3|
|Agropyron cristatum||Crested wheatgrass||Fairway, Ephriam, Douglas||200,000||4|
|A. cristatum × A. desertorum||Hybrid crested wheatgrass||Hycrest||175,000||5|
|Agropyron desertorum||Desert wheatgrass||Nordan, Summit||188,000||5|
|Agropyron sibericum||Siberian wheatgrass||P-27, Vavilov, Vavilov 2||163,000||5|