Ok so for the shoots argument, I have a couple sources.
First is the role Calcium plays in cell wall structure and strength, especially in young growing shoots. Depending on the plant, each shoot will contain a specific amount of calcium, that it calls for to have delivered that it maintains. The actual concentrations vary, but the result is the same, every single growing shoot, and especially the young ones, are consuming vast amounts of calcium. The growth rate of these shoots will impact this even more, such as the explosive growth rate in bloom or that of a young branch trying to make it big.
That information can be found here:
Calcium is an essential plant nutrient. It is required for various structural roles in the cell wall and membranes, it is a counter‐cation for inorganic and organic anions in the vacuole, and the cytosolic Ca2+ concentration ([Ca2+]cyt) is an ...
www.ncbi.nlm.nih.gov
Apple farmers are keenly aware of this, which is why during spring/summer they are constantly pruning their trees to prevent terminal growth. If they don’t do this they wind up with severe calcium problems that can ruin their entire harvest. While I have no farmers I can link to directly I can link you to a podcast from KIS Organics with Bryant Mason, a certified crop advisor. Episode 123, 10 minutes in.
Podcast Episode · Cannabis Cultivation and Science Podcast · 01/11/2024 · 46m
podcasts.apple.com
What this information tells us is, every growing shoot we have is consuming calcium, right at its tips, always. So for every shoot we have growing, a specific amount of calcium is automatically tied up for its use. The younger and more explosive the growth, the more calcium being yanked away.
If our roots aren’t big enough to provide an adequate amount of calcium, our yields and quality will suffer. Dramatically in some cases, like bitter pit in Apples or blossom end rot in tomato’s.
This is also why calmag is recommend at the start of bloom. The growth rate of the shoots explodes and requires quite a bit more calcium.
You can take this a step further with a Calcium Use Efficiency formula and find out right where your own personal sweet spot is with some testing. The formula would be Shoot yield per unit of Ca accumulated in the shoot. That would be super useful for someone with a bottom line or a lot of boredom.