Total soluble salt is usually reported as electrical conductivity. As the salt load in the soil increases, the value for electrical conductivity will also increase. Typically, AgSource Harris performs two different tests. The first test is a fast and simple procedure. A slurry of soil is made using a 1:1 ratio of soil to water. This procedure is best for determining if the soil has a high salt concentration and monitoring its level from one year to the next. It answers the question, "Is the salt concentration increasing or decreasing over time?"
The second test is the saturated-paste method. This involves adding only enough water to saturate the soil. A coarsely textured soil will need less water than a heavy clay. As a result, this method is more "truly" calibrated to the salt concentration encountered by plant roots. Therefore, the saturated-paste method is best for determining potential crop injury. The table below shows the interpretations for the two salt determination methods. When looking at salt interpretation tables, it is important know which method is being used because most interpretation tables will just state salt concentration without stipulating the method. As you can see in the table below, the 1:1 ratio is about half of the saturated paste. Slurry
1:1 Extract | Saturation Paste
ECe | Saline Classification |
| | mmhos/cm | mmhos/cm | | | | | 0.01 to 0.45
0.46 to 1.50
1.51 to 2.90
2.91 to 8.50
> 8.50
| 0.01 to 2.00
2.01 to 4.00
4.01 to 8.00
8.01 to 16.00
> 16.00
| Salt sensitive plants can be grown
Sensitive plants can be affected
Medium tolerant plants can be affected
Most plants will be affected
Severe saline conditions
|
Top
Salt-concentration tolerances, based on saturated-paste method, for commonly grown crops based on maximum acceptable yield losses are shown below: Maximum Acceptable Yield Loss | Maximum Acceptable Yield Loss | | Crop | 0% | 10% | 25% | 50% | 100% |
Maximum ECe Concentration (mmhos/cm) | | Bermuda grass
Barley
Alfalfa
Corn
Soybeans
Wheat
Oranges
Grapes
| 6.9
8.0
2.0
1.7
1.0
6.0
1.7
1.5
| 8.5
10.0
3.4
2.5
1.5
7.4
2.3
2.5
| 10.8
13.0
5.4
3.8
2.3
9.5
3.2
4.1
| 14.7
18.0
8.8
5.9
3.6
13.0
4.8
6.7
| 22.5
28.0
15.5
10.0
6.5
20.0
8.0
12.0
|
Note: Salt tolerance is much less during germination for many salt-tolerant crops. Salt-tolerant crops require ECe less than 3.0 mmhos/cm during germination. This table of maximum salt concentrations and corresponding yield losses assumes average soil moisture conditions are maintained throughout the growing season. If soil moisture conditions are higher than average, yield loss will be less than that stated in the table. On the other hand, as soil dries out, salt concentration increases along with salt injury. On average, salt concentration doubles as the soil dries from saturation to field capacity. It doubles again as it dries to wilting point. For example, a saturated-paste salt concentration of 3.0mmhos/cm would be about 6.0 mmhos/cm at field capacity and 12.0 mmhos/cm at permanent wilting point.
Top Type of Salt
The big three soil salts are calcium, magnesium, and sodium in combination with chloride, sulfate, and bicarbonate. The most important salt is sodium because of its potential to destroy soil structure and reduce water infiltration. As the proportion of sodium absorbed in the clay increases, the soil tends to disperse or "run together," bringing about reduced rates of water penetration. However, soil sodium alone provides little information about the potential effect on soil structure and water infiltration. The dangers of soil sodium are best expressed as a ratio to calcium plus magnesium. Based on this concept, the sodium absorption ratio (SAR) was developed to express the soil sodium danger. SAR above 15 is expected to be more of a problem for a heavy textured soil versus a sandy soil because heavy textured soils have low infiltration rates under good conditions. Soil boron concentrations are rather low in comparison to the other salts, but are important to mention from a toxicity standpoint. Soil boron concentrations below 0.7 ppm are safe for sensitive plants, 0.7 to 1.5 ppm is marginal, and more than 1.5 ppm is toxic to many crops. Conclusion
Soil salinity and alkalinity are best managed by knowing soil salt concentrations and salt type. Interpretation tables for salt concentration and salt type are based on the saturated-paste extract. Soil salinity ECe values less than 2.0 mmhos/cm are safe for most crops. With ECe values above 2.0 mmhos/cm, yield loss is highly crop specific depending on crop-salt sensitivity. Salts that contain sodium are dangerous to soil structure and water infiltration. The ratio of sodium to calcium plus magnesium (SAR) reflects the true soil-sodium danger. Soil with SAR above 15 is prone to drainage problems. Copyright © by AgSource Harris, a Division of Cooperative Resources International | 
