Repeated irrigation with water containing 1200 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 being flushed with fresh water from rainfall or irrigation, can create a problem by allowing salts to accumulate in the root zone of the soil. October 1 through November 15 is overseeding time along the coast. Turf-type perennial ryegrasses have only medium tolerance to salinity. Test the soils for salinity before overseeding to avoid a loss in stand of winter cover.
Gypsum works best when incorporated into the soil but it can be broadcast on the turf.
Gypsum is not very soluble in water but it is more soluble than limestone. Irrigate after gypsum application to move it into the soil surface and root zone of the turf. Allow a period of time for the chemical reaction, then continue irrigation to leach the salts into soil below the root zone. Poorly drained soils will be difficult to leach. Water logging the soil for extended periods of time can be as harmful to the turf as excess soluble salts.