In-field Diagnosis

Visual symptoms can be used to identify these problems, but ultimately a soil test is the best way for an accurate diagnosis. When salinity is suspected from a high water table, you may be able to measure ground water depth by boring holes with an auger. If free water collects in holes less than 4 to 5 feet deep, a drainage problem is indicated.

Salt impacted field.

Normally, high pH or basic soil doesn’t look different than soil with neutral pH, although sometimes the soil may have a powdery substance on the surface. Plants growing in these soils sometimes give clues about the problem. High pH reduces the availability of some nutrients (zinc, iron, phosphorus). Signs of high soil pH include yellow stripes on middle to upper leaves (signs of zinc and iron deficiency); or dark green or purple coloring of the lower leaves and stems (signs of phosphorus deficiency). Looking for symptoms is useful when growing high pH sensitive plants such as dry beans, sorghum, or silver maples. Corn and wheat are moderately susceptible to high pH and may also suffer from nutrient deficiencies on these soils.

Plants growing in saline soils may appear water stressed. This is because the high salt content of the soil hampers the ability of plants to take up water from the soil. Water naturally moves from areas of low salt content to high salt content. Sometimes a white crust is visible on a saline soil surface. Plants that are sprinkler irrigated with saline water often show symptoms of leaf burn, particularly on young foliage.

If a soil is sodic, a brownish-black crust sometimes forms on the surface due to dispersion of soil organic matter. Dispersion of soil particles also results in crusting and impaired drainage. Often you will first notice reduced seedling emergence and viability. By the time darkened crusts are visible on the soil surface, the problem is severe and plant growth and soil quality is significantly impacted. Laboratory analysis of soil is the best way to diagnose these problems before plant growth is severely damaged.

Laboratory Diagnosis

Soil testing labs typically evaluate pH and EC (electrical conductivity) as part of a routine analysis. If the pH is high (>8.5), sodium adsorption ratio (SAR) should also be calculated. See Table 1 to evaluate the lab results.

If you suspect salinity or sodicity problems, collect a soil sample from the top 6 to 12 inches of soil, concentrating on the areas that appear most impacted. High pH, salt or sodium levels are rarely uniformly distributed across fields. Areas of the field suspected of these problems should be mapped and sampled separately to fully understand the severity of the problem. Be sure to tell the laboratory that you suspect a problem and ask that they analyze for SAR or ESP and perform a gypsum test, if necessary.

If you are irrigating the site in question, collect a water sample for analysis as well. High levels of salts and sodium may come from irrigation, a high water table, manure or fertilizer inputs, or from the soil parent material. To effectively manage the problem, you need to know the source of the salts. Although 4.0 dS/m is used as a threshold EC to define saline soils, some sensitive crops will show symptoms and reduced yields at lower ECs.

What Can be Done After Diagnosis?

There are several management options available once the extent of the problem and its source are properly identified. See Colorado State University Extension fact sheets 0.503, Managing Saline Soils; 0.504, Managing Sodic Soils; 0.506, Irrigation Water Quality; and 0.520, Selecting an Analytical Lab for more information.