What Is the Difference Between Saline & Sodic Soils?

Saline, alkaline soils continue to pose problems for farmers

What Is the Difference Between Saline & Sodic Soils?

by Renee Miller, Demand Media 

The pH level of your soil is a primary indicator that salinity or sodicity may be a problem.

Saline and sodic soils limit the ability of a plant’s roots to absorb water, and they also destroy the soil structure by breaking down and dispersing soil particles. This can negatively affect seed germination and root growth. These conditions are different soil problems that cause different symptoms and issues. However, management of saline and sodic soils requires only slightly different methods.

Definition

Saline and sodic soils both have high pH levels, with problems typically occurring at a pH of 7.8, or extremely alkaline conditions. The primary difference is that saline soils also have a high salt content, while sodic soils have high sodium content. Soils may also have both high salt and sodium contents at the same time. When referring to saline soils, salt content describes soluble salts in the soil, which include the chlorides of sodium, calcium and magnesium, as well as carbonate salts. These are high enough to affect plant growth and cause plant death. When referring to sodic soils, the level of sodium in the soil dominates the other soluble salts.

Saline Soil Symptoms

Because alkaline conditions limit the availability of nutrients such as iron, phosphorous and zinc, you’ll see symptoms of saline soil in plant leaves, including yellow stripes on the upper leaves caused by zinc and iron deficiency, or dark green or purple coloration of stems and lower leaves caused by phosphorus deficiency. Drought symptoms such as wilting or yellowing of foliage are also common in saline soils. You may also notice a powdery substance on the soil, as the salts are dispersed to the soil surface.

Sodic Soil Symptoms

Plants growing in sodic soils may show drought symptoms like those growing in saline soils, but sodic conditions also reduce the viability of seedlings and can negatively affect germination. Sodic soils may also develop a brownish-black crust that is caused by the dispersion of organic matter. Once this crust is visible, the problem is usually severe and plants will already show signs of stress.

Diagnosis

While visual symptoms are helpful in diagnosing saline or sodic soils, a soil test is needed to accurately diagnose and treat the problem. Collect a sample from the top 6 to 12 inches of soil and take it to your local agricultural extension office, where professionals can test the soil and then recommend solutions.

Management

Periodically increasing the water you give your plants may leach the salts from the soil, provided your soil has good drainage. Another option for saline soil management is to plant salt-tolerant plants that have deep roots to help draw the salts from the soil. For example, magnolia (Magnolia grandiflora), which is hardy to U.S. Department of Agriculture plant hardiness zones 7 through 9, and periwinkle (Vinca major, Vinca minor), which vary in hardiness typically ranging between zones 4 and 11 are both highly tolerant of saline conditions. To manage sodic soils you must replace the sodium with calcium before leaching the sodium from the soil. This can be accomplished by dissolving the calcium carbonate (limestone) or calcium sulfate (gypsum) in the soil with the application of sulfur or sulfuric acid. If your soil test indicates that calcium carbonate or calcium sulfate is not present, adding calcium in the form of calcium chloride or gypsum may reduce sodicity. These are typically broadcast over the soil and watered in, but according to the University of North Dakota, the exact amount of amendments like sulfur, gypsum or calcium chloride you should add depends on the level of sodicity indicated by your soil test.