What is salinity index?

Carmen -

The salinity index measures the direct relationship between Electrical Conductivity (EC) and moisture. This ratio tells you the concentration of salinity in the available moisture. For instance, with moisture being consistent and EC rising, salinity concentration will go up and salinity index will rise.

We developed the salinity index measurement to offer further insight into how salinity impacts turf performance. We've found that even though a soil test report showed proper balances, we still found nutritional issues in the turf due to stresses. So many people focus on just the EC value.

Remember that EC is a measurement of ions in solution. The movement of + and - ions causes electrical current aka EC, which impacts how the turf responds. The more ions moving the more EC. Those ions require moisture to move. As the turf dries, ions bond together and precipitate out into solids that bind to soil particles, root, tissue fibers, and organic matter. As the moisture rises, these ions go into solution, if the chemistry is correct, and begin to drive EC again.

The ideal salinity index is somewhere around 1.0. However, if you have high ion concentrations in your irrigation source or you fertilize too often, you will see higher numbers on average. You can change your warning appropriately for your course. For instance if you are on effluent, reclaimed, or even brackish influenced well water, most will set this target around 1.6 as it is very difficult to fall below that.

Once set, use POGO to help develop more uniform conditions using the DU score. The higher that number, the better. When you achieve strong DU, maintain consistent moisture on your turf through improved irrigation and cultural practices. From that point you can use the salinity index to indicate residual salts from your fertility program to gauge salinity as the turf sees it.

Finally, just because EC rises does not mean the salinity index will rise. Sometimes just a change in moisture is all the turf needs. Use both numbers to help you dial in your program!