This might be a bit of a newb question, but here goes:
Are hydro and soil-less medium grows normally fed chemical nutes, while soil grows tend to be (but are not always) organic?
If so, why is this and what are exceptions to those?
Yes....the reason why is complex. I’ll try to be brief lol...
Organic soil is made up of millions of different living things along with non living organic materials. It is alive; among many other things soil contains microbes that break down organic materials and fungi that attaches to the root systems of all plants. The level of microbial activity in the soil has a lot to do with how healthy it is, how long it can sustain plants, and is also related to ph and soil composition. The soil make up, microbes, and mycorrhizae fungi form a symbiotic relationship that benefits all; aka the soil food web. So that being said all a decent organic soil needs to function properly is water.
In a sterile hydroponic medium you must provide soluble nutrients that can be absorbed directly by root systems without assistance by fungal symbiosis. The medium is only there to hold roots in place; the nutrient solution is adjusted to the proper ph for absorption as there is nothing to buffer it externally.
Synthetic nutrients feed the plant everything all at once whether it is needed or not whereas in soil the plants take up only what they need as it is needed. This is why over feeding leads to burn and/or salt buildup. You can use synthetic nutrients in both soil and sterile mediums but many are not safe for living soil. There are soluble organic nutrients and fertilizers that are safe for living soil; look for the OMRI label.
Keep a few things in mind:
No matter what you feed the plants it will eventually be deposited into the flesh of the plant. This is why grapes from different regions have different characteristics when they are made into wine: it is the soil composition (minerals, activity, etc) that makes the difference. This is also why synthetic nutrients must be purged from the medium regularly to prevent buildup.
Nobody feeds the trees in a forest yet they grow tall and thrive for hundreds of years. Soil was once leaves, animal carcasses/feces, minerals, and many other organic materials that have been broken down by microbes and distributed by mycelium underneath the forest floor.
The plants don’t really care what you feed them as long as they get what they need whether through symbiosis or directly soluble means. Many growers have found a balance between nutrients and soil but some do not realize they are using their soil as a sterile medium and probably would be better off using something like coco. Some might think their soil is depleted when in fact it had simply become inactive. PH and microbial activity are also closely related.
Compost is the main source of microbial activity on Earth; the gullets of earthworms contain the soil microbes needed by plants to decompose organic materials. This is why compost, namely worm castings, are so important to soil grows. EWC also usually what is lacking when growers have problems in soil.
There’s more to it than this but hope that helps answer your question..,