oh my,
yes--it can be rather complicated!
consider this: water conducts electricity, right?
As a sort of baseline, distilled water has a very, very low EC because the ions, all the various dissolved charged particles, have been removed.
A 'salt' is a generic term for any molecule composed of a positively charged particle and a negatively charged particle stuck together when they are dry or in a solid form. When the salt is dissolved in water it breaks apart into the individual charged particles, the ions--cations have positive charge, anions have negative charge.
The EC of water increases with dissolved salts--the flow of current in the water in the soil is proportional to the concentration of ions dissolved in the water. So, this gets measured and interpreted as the 'salinity' of the soil.
The thing is, though, the EC measurement does not tell you what ions are responsible for the increased conductivity. For that you actually need a measurement of the major ions.
Or you can guess based on your local soil type. Like in our area we have high sodium in our soil and in our irrigation water so, around here, a routine soil test is "pH, soil salinity (ECe), P, and K" and if the "pH is greater than 8.2 together with moderate to high salinity (ECe > 2 to 4 dS/m)" this is interpreted as "a problem with excess sodium." They then recommend confirmation with testing the sodium adsorption ratio (SAR).
This is certainly an example of 'bad' salt.
It drives me crazy that the routine soil tests around here do not measure the major cations and we just assume sodium is to blame, but, like I said, we have high sodium so that's how it's done.
Other dissolved salt components, of course, are considered important nutrients for plants, (well, actually sodium is an important nutrient too, it's just bad in excess) like calcium and potassium.
In other areas with really sandy soil and lots of leaching, the EC is relatively low. People are actually trying to raise the EC by adding fertilizers and the EC is frequently used as a quick measurement to monitor this.
From my perspective, it seemed to me like the takeaway idea of the book (or at least the portions I read) was to
1.) analyze your soil and 2.) amend based on the results instead of guessing
So for example--if I have high pH and high EC, with sodium and magnesium excesses, it might actually help a lot to displace some of the sodium and magnesium with calcium. The goal and the result, if done properly, would
not be to increase the EC by adding salt, but rather to change the relative proportions of the major cations involved in the already high EC.
Now, if only I had rain water!!
