What are counterion effects?
Here is a passage from Marschner P. (2012). Marschner’s mineral nutrition of higher plants. 3rd Edn. London: Academic Press:



In the context of the wikipedia table, it means that while you can have a high concentration of sulfate, you should consider the cation of the substance (e.g. calcium sulfate, potassium sulfate, ammonium sulfate) as well when trying to figure out the effects on a plant.