Too much K screws with magnesium absorption. This is a critical problem. humans have haemoglobin which is formed around iron. If you replace that iron with magnesium you have plant blood, chlorophyll. is the heart. So, of photosynthesis.
It is very quickly depleted so when plants are not responding to single dose treatments, it may be because they are running out of this element too fast every time. Remember each strain and to some extend phenotype, have different nutritional demands. If everything else is going well I would not increase potassium unless the flowering stalls.
I see your point, yet I'm not raising to toxic levels or levels that have screwed my Mg uptake...Not at all. I assure you, I have
no Mg problems. In my organic wo soils or in the synthetic runs I'm doing right now.
I'm also a everyday water/feeder in the use of synthetic's, so no "running out to fast" problems there.
In the WO soil builds. I go for 2 of 3 bloom soils being amended with differing release timed "extra" K. For longer running plants. The 3rd is a fast plant faster release higher K soil. These soils have
plenty of available Mg.....and I have never had an uptake issue with Mg in them. This would seem to indicate that the plant is not being feed a tox level amount....eh?
Now and then (with the organics), might supplement a bit more K by teas near the end. If the plant "looks" like it needs more to fill
my requirements from years of doing it....As you might guess. I grow by "what the plant tells me" visually. Some natural schedule has been ingrained over the years and of course the plants tolerance's to what I'm feeding.....It's like it's following a very well worn path, that you began decades ago..... After finding what has been
your best route to the destination..
I believe that our plant has a higher need/tolerance for K then many other C3 plants. That's just a simple observation and has it's own "limits". I see that difference all the time on the farms......Squash has very little tolerance to any elevation of K. Cruciferous vegetables have more but, still quickly loose yield from elevated K. This makes sense as you tend to have these crops in more moist soils and that increases K availability.....You don't amend the soil for K, you rotate to a lower K using plant for that area next season. Alfalfa and grains like higher K amounts in soil and alfalfa actually does best with plenty of available K. This makes for the use of manures being well suited for use as ferts on those area's....Same for limited use on cruciferous fields but, not for squash fields!
This is what I have found in Cannabis as expression of K
overuse in veg: Reduced growth followed by symptoms of iron chlorosis, stunting, reduced branching, color expression in new growth that can increase out, and abnormal darkening and thickening of roots.
In bloom: Reduced growth followed by symptoms of iron chlorosis, stunting. In severe case's (you do see this around here too) necrosis starting on the edges of leaves and moving inward.
This is a severe case (pic from cannabis.com)
This is somewhat advanced excess K expression in squash. More like it was ferted poorly and responded quickly to the problem.
Early in squash is light yellowing followed by light tan necrosis on the leaf edges, going about 1/8 to 1/4 inch in....