Interesting points:
Any idea how much yield reduction you would expect if running staggered veg and flowering and one size fits all nute soup (all 2' - 5' plants veg and flower)?
Zero grams.
I already use the same soup for tubes (flower) as DWC (veg). I.e. After mixing a fresh batch in the large rez I use some of it for dwc (or hempy or coco but then I do ). They are however not connected to the same rez so I can mix a soluion for it separately, and top off separately.
Zero because running lower ppm does not equal underfeeding, just means you have to top off with nutes more often to keep it from really dropping too low and prevent imbalance. The whole concept of flower nutes is largely bs but one could simply run a little more A than B in veg and a little more B than A at the end (A is high on Ca and N, B high on P).
It's actually quite normal in large hydroponic greenhouses where plants of various age and size are in the same tray or bath.
A larger plant transpires more, has more root mass, so already takes up more nutrients. I.e. A larger plant does not necessarily require a high nutrient concentration, but will use more nutes regardless so will reduce the nutrient level in the rez faster.
So the larger flowering plants take up nutrients faster than the seedlings in veg, which means the EC will drop faster and you have to add nutes more often.
There's from the plant's perspective really no reason to stay on that socalled sweetspot where water uptake and nutrient uptake is balanced. Convenient for the grower, but all the plant needs is being able to take up enough nutrients over time. It can do that at 600ppm but also at 400ppm. The difference is that the 400ppm makes the rez ppm drop faster so requires more maintenance.
I think the common misconception about the sweetspot is caused by an assumption that drinking from a high ec soup equals more nutrient uptake. Which is not necessarily the case. True for Ca and perhaps a few others, and in soil drinking pulls nutrients to the roots (flow beats that) but nutrient uptake (cation anion exchange) is a separate process. The EC climbing or dropping does not directly say something about the amount the plant needs to reach its genetic potential.
Above all, unlike bloom boosters etc suggest, those few grams of nutrients are just a small factor. And then it's still the total amount of nutrients it takes up over time that's key, not the concentration of the soup it takes it from. Lower ppm is less stressful on the roots and plant which in turn maximizes allows for a more consistent nutrient uptake.
That run I did to see what the minimum would be was at 360ppm, half being tap, and I don't think it reduced the yield by a single gram (impossible to measure so exact because there are so many other variables). It would perhaps become obvious on a hectare sized grow, but if it's like 2-5% it's hard to notice in a single bulb grow. That's also exactly the ppm I start out with for seedlings (that rooted through the cubes).
