I'm not sure about this one. On one hand it sounds correct that plants would only use what they need, but plants do absorb stuff they don't need. Reminds me of the white flowers in blue food dye experiments at school. I can't say either way, the article does also mention that potassium does not appear to have a toxic effect on plants so apologies for my original use of the word 'uptake '.
I wander if too much potassium in the soil can somehow block the uptake of other nutrients? Perhaps by binding to them, as opposed to the plant taking in the potassium itself.
From the article:
'Potassium Toxicity
Excess potassium does not appear to have a toxic effect on plants. It can induce deficiencies of other nutrients however (particularly nitrogen, calcium and magnesium) so care should be taken to avoid an excess by only ever applying potassium containing fertilisers when required and according to the directions on the packaging.'