Interpretation of Mineral Soil Test Results for Salinity

Agricultural Service Laboratory, Clemson University

 

Soil Salinity (or soluble salts) in mmhos/cm (1part soil to 2 parts water method).

The total dissolved solids (ppm or mg/L) can be approximated by multiplying the soluble salts

(mmhos/cm) by 1280.

 

(Values in chart refer to the soluble salts in mmhos/cm)

 

Soil Textural Classification

Probable Relationship to Plant Growth

Sand

(<15% Clay)

Loams

(15-26% Clay)

Clay Loams

(27-40% Clay)

Clays

(>40% Clay)

Normal Range

0.05-0.15

0.10-0.20

0.15-0.30

0.20-0.50

Salt Buildup-CAUTION

0.15-0.30

0.20-0.50

0.30-1.00

0.50-2.00

Excessive Salts

0.30+

0.50+

1.00+

2.00+

 

Most salt problems develop directly from salts added by irrigation water, therefore,

salts must be removed by leaching before they accumulate and become a problem.  Proper

irrigation management and adequate drainage are essential to prevent salinity problems.

The only way to remove salts from the soil is by leaching them below the rootzone.

 

With adequate rainfall, leaching may not be required.  However, during drought

conditions, leaching by applying excessive irrigation water is necessary to prevent salinity

problems.  Where a restrictive soil layer prevents the downward movement of water, lateral

tile drains installed directly above the restrictive layer are needed.

 

To leach salts below the rootzone, “extra” water is needed beyond that required to

wet” the rootzone.  The amount of the “extra” water needed to leach salts increases with

turfgrass sensitivity and with the salt content of the water.  The best method to help prevent

the buildup of salts in soil is by watering turfgrass as infrequently as possible, but deeply

irrigating when water is applied.

 

Where restrictive layers develop in the rootzone, cultivation or aeration may be

required before attempting to leach salts through the soil.  Deep-tine aeration is an effective

way to improve water movement through a layer in the top 10 to 12 inches of the rootzone.

 

When sodium constitutes a significant amount of the salts found in soil or in the

irrigation water, additions of gypsum may be necessary.  The calcium in gypsum replaces

the sodium on the soil particles and allows water to move the sodium below the rootzone.

Soil tests will indicate the need for amendments such as gypsum.