Exchangeable Potassium

Can we think of the concept of exchangeable/active/residual acidity similar to non-exchangeable potassium/exchangeable potassium/Soil Solution potassium?

I.E. Residual acidity is H+/Al3+ trapped between clay minerals. Non-exchangeable potassium is K+ between clay minerals. Once the H+ and Al3+ ions become unbound, they are part of the exchangeable acidity which can be exchanged into the soil solution, just as exchangeable potassium is held near clay colloids, but can exchange into the soil solution? Kind of the same concept?

Furthermore, I'm not sure I fully understand how potassium increases drought tolerance. Is it just the fact that it is a solute in the soil solution that decreases osmotic potential, meaning water will tend to flow towards it.

Lucas, I would not mix concepts - although in this example both are related to exchange reactions.

1) active acidity - due to H⁺ and Al³⁺ ions in the soil solution; Exchangeable acidity - associated with H⁺ and Al³⁺ ions that are easily exchanged by other cations in the soil solution; and Reserve acidity - associated with H⁺ and Al³⁺ ions that are bound (non-exchangeable) on soil particles.

2) K cycle - the main sources of K are: minerals such as micas and K-feldspar (weathering releases K); SOM; and potash fertilizer (KCl a soluble salt). There is a gradation between exchangeable and "fixed" K. K⁺ electrostatically attracted to negative charges on soil colloids (e.g. clay or SOM) is exchangeable. The non-exchangeable pool contains less available K+ ions that are trapped in between the structure of the clays and are released slowly by weathering. The fixed or mineral pool contains K held within the mineral and so is very slowly by the weathering.

Regarding the role of K in drought tolerance it is my understanding that K plays a role in guard cell regulation and thus in the opening and closing of stomata.

Thanks Sandra!