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Saline Soils and Plant Growth

This article outlines plant response and ways to measure soil salt levels.

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Updated:

March 14, 2023

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Howard F. Schwartz, Colorado State University, Bugwood.org

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When salt-sensitive plants are grown on saline soils, plant injury can occur. In Pennsylvania, saline soils are rarely encountered because soluble salts typically do not accumulate as rain, snow, and other precipitation events effectively flush soluble salts out of plant root zones. However, we have heard from growers and have experienced saline soils with the use of stationary, four-season high tunnels. In this case, the protective plastic covering high tunnels excludes precipitation and leaching of soluble salts, which can then accumulate in plant root zones. High tunnels are also often equipped with drip irrigation systems. These systems use water efficiently; however, the small amount of water used does not promote leaching of salts.

Plant Response to Salinity Levels

Table 1. The effects of salinity levels on various vegetable crops.
Salinity Level (mmhos/cm)	Effects
Less than 0.40	Negligible salinity; salt-sensitive cultivars of beans and carrots may exhibit effects
0.40-0.80	Very slightly saline; 25-50% decrease in yields of carrots, onions, peppers, lettuce
0.81-1.20	Moderately saline; seedling injury possible; 25-50% decrease in yields of broccoli, potatoes
1.21-160	Saline; beets tolerant
1.61-3.20	Strongly saline
Greater than 3.2	Very strongly saline

*Adapted from the Agriculture Analytical Services Laboratory, The Pennsylvania State University; based on a 1:2 soil:water test.

In addition to affecting yields, salt injury symptoms include necrosis (burning) of leaf margins, stunted plants, wilting, and in severe cases, plant death.

Salt-sensitive plants are less able to uptake water from saline soils and can become water-stressed. Another way plants are injured is when sodium, chloride, or sulfate levels become toxic and cause nutrient imbalances with potassium and calcium.

Salt-tolerant plants respond to saline soils differently than salt-sensitive ones. Some salt-tolerant plants simply do not uptake excess salts. Others uptake excess salts but then excrete them through leaves. Still others store excess salts in cells (in vacuoles).

Testing for Soluble Salts in Soils

Penn State's Agricultural Analytical Services Laboratory will test the soluble salt level of soil samples. To request this, check "soluble salts" under the "optional tests" box and submit payment. Currently, the cost is $5.

Electrical Conductivity (EC) Testing

EC testing is used to determine salinity. Pure water (salt-free water) does not conduct electricity well. As the salinity of water increases, so does its electrical conductivity.

EC Units

Soluble salt levels are usually expressed as decisiemens per meter (dS/m) or millimhos per centimeter (mmhos/cm). These two units are equivalent and used interchangeably. For example, 0.40 dS/m equals 0.40 mmhos/cm.

Interpreting Results

Before interpreting results, it is important to match the interpretation with the EC method used. The Agriculture Analytical Services Laboratory uses the 1:2 soil:water method. Other methods are the 1:1 soil:water method and the paste method.

Table 2. Soluble Salts (Conductance) Interpretation for Soils (based on using the 1:2 water:soil EC method)


mmhos/cm 1:2 Soil_Water	Effects
<0.40	Salinity effects mostly negligible, except possibly beans and carrots.
0.40-0.80	Very slightly saline; but yields of very salt. Sensitive crops such as flax, clovers (alsike, red), carrots, onions, bell peppers, lettuce, sweet potatoes may be reduced by 25 to 50%.
0.81-1.20	Moderately saline. Yield of salt-sensitive crops restricted. Seedlings may be injured. Satisfactory for well-drained greenhouse soils. Crop yields reduced by 25 to 50% may include broccoli and potato plus the other plants above.
1.21-1.60	Saline soils. Crops tolerant include cotton, alfalfa, cereals, grain sorghum, sugar beets, Bermuda grass, tall wheat grass and Harding grass. Salinity higher than desirable for greenhouse soils.
1.61-3.20	Strongly saline. Only salt-tolerant crops yield satisfactory. For greenhouse crops, leach soil with enough water so that 2-4 quarts (2-4L) pass through each square foot (0.1 m2) of bench area, or one pint of water (0.5 L) per inch (15 cm) pot; repeat after 1 hour. Repeat again if readings are still in high range.
>3.2	Very strongly saline. Only salt-tolerant grasses, herbaceous plants, certain shrubs and trees will grow.