ProCrop 1999

MANAGING SODIC SOILS

Many saline soils in North Dakota also have elevated levels of sodium. High levels of sodium restrict water-holding capacity in two ways. First, sodium prevents soil clay particles from gathering together into small groupings. This process of gathering together is called flocculation. Flocculation allows water to penetrate between the groups of soil particles and provide moisture to deeper depths. When sodium levels are high enough to prevent flocculation, the individual clay particles overlap each other randomly during wet conditions, preventing water penetration through the high sodium layer.

Secondly, when the soil dries out, areas within high sodium soils form hard structures which look like round-topped columns. These columns do not allow roots to penetrate into the column, so the only water and nutrients which are available to plant roots come from the small surface area surrounding these structures. The plants are therefore allowed only a small percentage of the total possible volume of soil in which to grow.

Areas of high sodium can be suspected when soil pH is greater then 8. The areas can be confirmed by requesting a sodium test. Most laboratories equipped to analyze for potassium are also equipped for analyzing sodium.

The spread of high sodium areas can be checked by following the same management plan as for any salt problem. Decreasing the level of sodium may be much more difficult, however. Because of the restriction of water movement within the soil, leaching is more difficult.

If high levels of gypsum are present in the soils with high sodium, addition of gypsum will not help replace sodium in the soil. In these soils, deep plowing may help to mix the gypsum already present in the soil with the sodium bearing soil horizons. If the soils do not already contain gypsum, addition of gypsum will replace sodium with calcium in the profile.

Calcium chloride will perform an even faster remediation than gypsum. Calcium chloride is more soluble than gypsum, therefore needing less water to replace sodium within the profile. If the local economics are favorable for a calcium chloride application, it is the preferred sodic soil remediation amendment. Together with enough water and a deep enough water table which would allow sodium to leach away from the root zone, the soil can be improved by this amendment procedure. Sodic soil remediation should consider calcium chloride first and gypsum second when making a decision. It is important to note that any amendments and management will be ineffective in controlling sodium if the water table management recommended for salt management is not implemented at the same time.

SUMMARY OF SALINE SOIL MANAGEMENT TOOLS

1. Soil test for salinity levels and the extent of the problem in each field.

2. Select the right crop and variety for the situation.

3. Use shallow tillage.

4. Be patient and wait to plant discharge areas until salts leach from the planting zone.

5. Do not fallow if available water in the top 4 feet of soil is sufficient to grow a minimal crop, or if the soil texture is sandy loam or coarser.

6. Use long growing season, deep rooted crops to control the water table depth.

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