No, resistivity is another way to measure electrical conductivity or TDS. This measures how quickly a material can transfer electrons. Whereas voltage measures the full potential of exchanging electrons.

A full glass of water has 100% potential to spill water. An empty glass of water has 0% potential to spill water. Now if the glass had a coffee lid, that would slow down how slowly the water could spill, and that would be analogous to resistivity. Whereas conductivity is the inverse…how quickly it could spill. same thing, just inverted.

When reduction was first discovered it meant “reduction in oxygen content”. Now it means more than that, but lets stick the the first simple meaning, before trying to grasp the full meaning.

Eh is the potential for soil to be reduced, with hydrogen being the reference point. So everything is compared to hydrogen’s ability to gain oxygen. So how much potential is there for H2 to become H2O. Or H2O to become H2. In most cases it’s a measure of how much potential the soil has to lose oxygen (in comparison to the potential for H2O to lose oxygen) When there’s a lot of oxygen in the soil, there’s a lot of potential to lose that oxygen. When the soil is anaerobic, there’s low potential to lose oxygen.

The whole point of photosynthesis is to remove oxygen and put it in the atmosphere. But it takes energy/work to do this, so if the soil is too oxidized then the reduction potential is high, but it’s too much work for the plant. If the soil has no oxygen, then the work is low for the plant, but then the plant can’t do work. So the sweet spot, is where the reduction potential is just right for the plant to do the amount of photosynthetic work it needs to be healthy. All organisms are unhealthy with too little or too much work. And healthiest with just the right amount of work.

Same with pH. which is basically potential to gain hydrogen. low pH are solutions that have a lot of hydrogen ions…therefore low potential to get more hydrogen. High pH are solutions that have a little hydrogen ions and therefore a high potential to get more hydrogen.

All of these explanations are simplified, and not 100% accurate, but hopefully helpful in getting you closer to understanding.