Healthy soil is the hidden ingredient

I'm a gardening and landscaping enjoyer, but I am constantly confused about the bordering magical thinking surrounding dirt, among other aspects of growing things.

If you look at hydroponics/aeroponics, plants basically need water, light, and fertilizer (N (nitrogen) P (phosphorous) K (potassium), and a few trace minerals). It can be the most synthetic process you've ever seen, and the plants will grow amazingly well.

The other elements regarding soil health, etc, would be much better framed in another way, rather than as directly necessary for plant health. The benefits of maintaining a nice living soil is that it makes the environment self-sustaining. You could just dump synthetic fertilizer on the plant, with some soil additives to help retain the right amount of drainage/retention, and it would do completely fine. But without constant optimal inputs, the plants would die.

If you cultivate a nice soil, such that the plants own/surrounding detritus can be broken down effectively, such that the nutrients in the natural processes can be broken down and made available to the plant, and the otherwise nonoptimal soil texture characteristics could be brought to some positive characteristics by those same processes, then you can theoretically arrive at a point that requires very few additional inputs.

sure, we can make them grow well in a lab. but a natural system is so much simpler and elegant

Plants absorb nitrogen and CO2 from the air and store it in their roots; plants fertilize soil.

If you only grow plants with externally-sourced nutrients, that is neither sustainable nor permaculture.

Though it may be more efficient to grow without soil; soil depletion isn't prevented by production processes that do not generate topsoil.

JADAM is a system developed by a chemicals engineer given what is observed to work in JNF/KNF. https://news.ycombinator.com/item?id=38527264

Where do soil amendments come from, and what would deplete those stocks (with consideration for soil depletion)?

(Also, there are extremely efficient ammonia/nitrogen fertilizer generators, but still then the algae due to runoff problem. FWIU we should we asks ng farmers to Please produce granulated fertilizer instead of liquid.)

The new biofuel subsidies require no-till farming practices; which other countries are further along at implementing (in or to prevent or reverse soil depletion).

Tilling turns topsoil to dirt due to loss of moisture, oxidation, and solar radiation.

The vast majority of plants do not absorb nitrogen from the air. Legumes are the well-known exception.

It isn't legumes that absorb nitrogen from air. It is bacteria that lives on their roots.