I am incensed that you would put this topic in the "not quite science" forum!
There are several interactions between plant nutrients that can be considered:
1) Too much of one nutrient may block the uptake of another nutrient;
2) The deficiency of one nutrient may prevent a plant from utilizing another nutrient;
3) An imbalance of nutrients in the soil can change soil chemistry so that some nutrients are in a form unavailable to plants.
Aluminum becomes soluble in soils at fairly low pH, and K is not what soil scientists consider an "acidic cation," so I don't think the K vs. Al scenario you mentioned would make much sense. [Note to those with a clue about chemistry: soil scientists refer to certain cations as "acidic" and "basic," even though this idea does not fit into any accepted acid-base system.]
Some of the more well-known interactions include:
N & S -- deficiency in one prevents utilization of the other (excess of one may also result in a deficiency of the other);
N & K -- similar interaction as N & S;
Cl can inhibit N uptake, but this may be a result of too many salts in the soil;
High pH can render Zn, Fe and others unavailable to plants;
P and many of the micronutrients (like Zn, Fe, Mn, etc.) form insoluble compounds in soil, rendering both P and the metal unavailable, this is more of a problem in calcareous soils.
K may retard the uptake of Ca and Mg, but I've heard different stories on this. The mechanism for uptake is different for K vs. Ca & Mg -- K having active uptake, while Ca and Mg are taken up passively.
Surely this sort of thing is in your text books? All this is from memory, so I would double check any *fact* that I've posted here.