There are four bases to achieving high brix soil:
1.)Foundational minerals. These are your rock powders, Limestone, Soft Rock Phosphate, Gypsum. Other things could conceivably be used as well, but those are cheap, reliable and available. The single most important mineral for High Brix is Calcium, followed by Phosphorus.
2.)Soil Energy. ERGS (Energy Released per Gram per Second). No energy in the soil, no growth of the plant. Fertilizers, organic material, salts....all increase ERGS.
3.)Soil Biology. These are the microbes, nematodes and fungi that inhabit the root zone and break down all the organic material and present it to the plant. We accomplish proper soil biology with humus and we boost it with microbial teas and root inoculates.
4.)Trace Elements. The "micro's." Magnesium, zinc, boron, iron, manganese, copper, molybdenum, sulfur, etc.
We don't put these things in the soil in the typical NPK ratio's that you see on plant food bottles. These things go into the soil in order to make the soil biology happy. For example, most of the phosphorus isn't available to the plant at all. Same with the calcium. But the microbes love it.
The plants, courtesy of the soil life, get anything they want, as much as they want. They never burn, they never lack.
That's the soil.
You supercharge the Brix in the plant tissue via Foliar Feeding. Phosphorus is the "shipping specialist" in the plant. Most things the plant needs come piggy backed as a phosphate, so increasing the phosphorus and calcium levels in the plant increases the sugar content in the leaves, which the plant sends down to the roots in the form of "root exudates." These root exudates feed and signal microbes and fungi that live on the roots, and they take the sugar and use it to form humic/fulvic acids so they can digest minerals and organic matter and feed the plant.
The foliar sprays act like a supercharger, while the soil acts like a gas tank. The microbes are the engine.....and the plants are the passengers who enjoy the ride.
That's High Brix.