Ok, grab a coffee.
RR those are solid readings
. Your soil is working well and also nicely balanced if you are in the mid to upper teens. Well done!
Follow that line, it will easily tell you 2 things. One is the state of the calcium, which is vital, and 2 is the amount of sugars that your plant has created and stored by the end of the day, and sugar in the leaf is a direct reflection of how well you photosynthesized during the day. So 1 is the state of your calcium, and 2 is the state of photosynthesis.
Now here is where it gets a little tricky. To raise photosynthesis, and this applies if your brix is 7 or 17 or 23, think of each day as a lap.
The plant takes in nutrients at the root, moves it up to the leaves, and photosynthesizes it into sugars, which are carbon based energy molecules.
Then the plant uses as much sugar to function as it requires and pushes the remaining sugars down to and out of the roots. That sugar going to the soil is called exudates.
It feeds myco, which is a fungus that lives in the dark so cannot photosynthesize it's own sugars to get carbon, and the soil microbes that require carbon. The fungus in return tells the roots where to squirt those exudates so the microbes will eat the sugary dirt to create the poop that contains what the plant requires that day.
Then that poop (plant food) goes into the root and the next lap starts.
So in most peoples minds photosynthesis is created by light exposure, and they aren't wrong, but the amount of light exposure both in intensity and volume over the day must not be greater than what that lap can create for food into the root, or the plant will suddenly require more food than it can get for the intensity of the light and the forced photosynthesis rate.
So what that translates into in plain english is if you crank up the light to speed up growth, then don't force growth to be faster than what the roots can provide or the plant will rob the missing ingredients it needs to keep up to the high rate of photosynthesis, from it's lower leaves.
By turning light too high, mathematics says you will create a deficiency where there actually isn't one. Make sense? The roots simply can't keep up.
So you need to get the most out of every lap and if your plan is to raise your brix higher then you can turn your light up but only a small amount, let a couple laps go by so myco forces more root growth with exudate placement, so the plant can keep up with photosynthesis from the soil not the leaves. Patience and balance are key here.
At a certain point above 18 brix and usually about 20.5, strains start to hit the wall. Their DNA simply does not allow higher photosynthetic rates.
Some strains are capable of 23's or 24's and my personal highest was a 26. That was the plant more than me as I didn't do anything differently but the plant had higher abilities.
So now you can plainly see the value in a big rootball. If you concentrate on growing your roots to always be bigger and stronger than what the plant needs for the next lap you are golden. Grow the roots and the foliage will just happen. So will brix and plant health.
We all judge plants by how pretty they are, and how big, and we like to show them off, and thats a beautiful thing as we love our plants and should be proud of what we grow, but if you think about it for a sec, we should be showing off our rootballs for bragging rights, because thats where potential lies. So balance is key or you will damage leaves, and damaged leaves can't grow the roots as well as healthy leaves.
You are about to cross the threshold into true high brix, and everything above becomes vital as you are close to the edge and need to be cautious that you don't get greedy and try for too much at once. Do your laps.
Then it comes down to ensuring you have minerals and light available, and the 5 key things for high brix. Calcium, phosphorus, carbon, oxygen, and healthy microbes/fungii.
Calcium is 1st on the list. It ensures tilth which allows oxygen, so it's a two-fer, and it sets your cation platters which supply minerals, so now it's a three-fer, and the balance of those minerals on the cation platters sets soil ph, as the last few platter spots are filled by hydrogen. Thats a large part of how calcium buffers PH in soil.
Phosphorus needs to be in balance with calcium and is vital for creating ATP, which is the energy that powers the laps, and ATP is created thru photosynthesis, so again balance or you run out of energy.
Carbon for photosynthesis comes from atmospheric CO2, not soil carbon. Soil carbon is microbe food not plant food, and what is left behind when the microbes eat it is the husk of the carbon molecule.
That husk is the cation platter that we talked about above that calcium balances both mineral flow and PH on. It's called a humate, or soil humus. Clay particles called colloids also perform the same function as a humate.
Healthy microbes eat more soil carbon creating more humates to supply more cations, so the laps help here too, as you need more cations today than you did yesterday, so it's part of the laps.
Oxygen is what microbes breath just like us, and in soil, water and O2 share the same passage ways and those passages are created by tilth (the fluffiness of the soil), and tilth is created by calcium's charge. Think static cling fluffing dust here.
So calcium builds the hallways that O2 and water share.
Now basic math applies and the more water in the hallways then the less room for air, and every speck of food created must have an O2 attached to it by the microbes in order for the plant to recognize that food as food. It's how plants know what to eat.
So overwatering causes starvation by oxygen deprivation.
If you get Calcium, Phosphorus, Carbon and O2 correctly balanced, you get very healthy microbes because exudates are now bountiful and exudates are pure carbon squirted on the dirt that the plant wants, and healthy microbes can eat more sugar-dirt in a day than unhealthy microbes can.
It's a closed loop and only as strong as the weakest link, so do your laps, maintain balance, and when everything can keep up without deficiency then turn your light up a smidge, watch carefully, create more exudates to build better microbes that can keep up, and repeat.
Eventually you either reach the plant's DNA dictated maximum or you reach deficiency. Or you can be very happy and content in the mid to upper teens and enjoy healthy robust plants that are bug free and grow great weed hasdle free. You don't actually need to push brix higher once you reach 17's and 18's, but heres the good part. If you get to where you are at and can maintain it the soil will take on a life of it's own and continue to raise brix until it naturally finds it's limits for what's in the pot, and all you have to do is maintain. High brix will naturally provide higher brix. The rich get richer.
Now think ahead to your next hrow. Would you want to start it with used soil full of exudates and healthy microbes and dormant myco spores from really healthy myco, or would you rather rebuild from soilvwith low sugars and poor microbes/fungii?
You really do have opportunity to pay it forward to yourself here, and if you do you will hit 20 in veg next round with the rebuilt soil as you have raised the floor at the starting line.
You need soil carbon as it's microbe food and humates, and it absorbs water to hold it for the plant, but not in the hallways, and overwatering is the fastest way to piss off a plant. Now you know why
This whole cycle is referred to as synergy, so if someone says your synergy appears off, this is what they mean.
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