Yes it is just like nitrogen is nitrogen whether it is in the form of urea, ammonium, nitrite, or nitrate. But perhaps you're talking about the compound and I'm talking about the element in which we're both right. My point was that I don't understand how biochar would be any more favorable than some of the other potassium products out there whether it was wood ash, potash, etc. If the compounds that include the potassium as a source (you mention carbon) then that mechanism is what I would like to know about and how it produces any competitive advantage over any other product. Addition of organics and improved aeration could also be accomplished by other means. Anway, 'not trying to debate since I think we're both talking about apples and oranges.
I grow citrus which are more nitrogen feeding that potassium, but I also foliar feed with trace elements every now and then. Citrus sometimes show signs of magnesium deficiency.