Soil salts affect turf mostly by withholding moisture from plant tissues. They may also compete for uptake of nutrient ions. Salts will destroy soil tilth and cause much-reduced water percolation rates.
Irrigation with clean, low-sodium, fresh water is probably the most important practice to follow when leaching salts from the root zones of soils, but with lower percolation rates, this could take several months. That is why a good rainy season is usually much better for turf than a lot of irrigation.
Try these suggestions to manage a soil salinity situation:
- Test all irrigation water sources for water quality. LSU Soil Test Lab has a Routine Water Test Package. If the irrigation lake has been flooded with brackish water, pump it out and fill with clean, good-quality water (or irrigate from the well or river if they are not contaminated with salt). Soil salinity may be from ‘bad’ salts like sodium, or it may be from ‘good’ salts as in over-applying fertilizers. If over-fertilizing is the problem, flush with fresh water and adjust your fertilizer program to follow soil test recommendations and use higher grade fertilizer materials.
- Bermuda, zoysia, paspalum and St. Augustine turfgrasses have good salinity tolerance and should be the grasses of choice. Tall fescue and perennial ryegrass have medium salinity tolerance. Centipede and carpetgrass have poor salinity tolerance and may not be sustainable.
- Repeated irrigation with water containing 1,200 ppm total soluble salts will be harmful to the turf unless followed by sufficient rainfall or fresh irrigation water. Even irrigation water containing 500 to 600 ppm total soluble salts, when used repeatedly without adequate flushing with fresh water, can create a salinity problem. If you depend on rainwater to flush salts, avoid letting turf dry down much between waterings if rain is not adequate. Lower soil moisture, without fresh water flushes, will concentrate soil salinity and stunt plants more. Louisiana falls can be dry unless we have tropical depression activity.
- October 1 through November 15 is Louisiana overseeding time. Perennial ryegrasses have only medium tolerance to salinity, while annual ryegrass has less. If you suspect a problem based on site history, before overseeding test the soils for salinity to avoid a loss in stand and waste of money. You can also try a pinch of your seed on the soil in question and do your own "bio assay" of the current salinity effect; use similar but nonsaline soil as a comparison check.
- Gypsum (calcium sulfate, 17 percent sulfur, 22 percent calcium) can be used to help leach salt from the soil exchange by replacing salty cations with Ca++. Gypsum works much better when incorporated into the soil surface, but it can be just broadcast on the turf. Gypsum is not very soluble in water, but it is more soluble than limestone. Irrigate well after gypsum application to move it into the root zone of the turf. Allow time for the chemical reaction, then continue irrigation to leach the displaced salts into soil below the root zone. Poorly drained soils will be difficult to leach, so allow several months. Waterlogging the soil for extended periods when it's hot may be as harmful to the turf as excess soluble salts. Core aerification or deep tine aerification (preferably with coring tines) can help improve movement of water, gypsum and salts through the soil and below the root zone.