Pogo Turf Pro System Manual page 86

Salinity Index
The salinity index is calculated in real time with every sample taken using the POGO Turf Pro app. While EC (salinity) is indicating the total EC
activity in dS/m as the turf sees it, salinity index indicates the concentration of those salts in solution. In early turfgrass courses we learn about
something called leaching requirement. It is the estimated amount of 'extra' irrigation you have to put out given an increased amount of EC
activity. As salts go up, the competition for the available water (between the turf system and the salts themselves) also increases. In other words,
it is harder for the turf to get the moisture it needs when EC increases. It is the EC concentration (salinity index) that really indicates this
competition.
Say you have a given amount of EC activity in a given amount of moisture. The competition for that moisture is at a certain level that may or may
not be tolerable by the turf. If we only increased the EC and kept the same amount of moisture, the concentration (salinity index) increases and
thus the competition for that available water gets greater. If we proportionately increase EC with moisture, then the competition remains the
same until we hit a certain level of EC that is detrimental no matter what the moisture level is.
On the flip side, say we dry down a system. If our salinity concentration is high at low moisture levels, the moisture that is present is all but
unavailable to the turf system and we can see rapid deterioration of vigor and performance while dehydrated conditions will ensue. Bottom line is
that not only is EC important but the concentration of the salts in solution is equally important, if not more.
Researchers may explain that as moisture goes down, we should see the EC level go up. This is a misunderstanding in the industry because this
does not give you the whole picture. Researchers are referring to the lab extract analysis process where a turf soil sample is saturated for a period
of time and then the solution is sucked out of the soil while the EC level is measured. That EC is based off of a 'Saturated Paste Extract' which is
the nature of that test. So it is not assumed that as the saturated paste extract test becomes something like 'Less than saturation paste extract'
salts too will go down. It is assumed that salts remain the same or at a higher concentration because the moisture dropped. Be careful not to
misunderstand this point. POGO measures EC in real time, as the turfgrass sees it. If salts are present and bound up in the turf system waiting for
moisture to put those salts into solution and thus increase the EC activity, then yes, as moisture rises, EC too will rise. This is NOT always the case
as we explain further.