sylvestris
Well that's a debate that will probably last the ages, and there are fanatics on both sides. Much like regular
nutrients vs organic nutrients in hydroponic systems, again fanatics on both sides. And both sides can get good results. Bottom line a healthy plant wont be lacking any vitamins and/or minerals (soil or hydro).
But realistically it all comes down to the growing conditions. Plants don't know if their in soil or a
hydroponic system, they don't know if they are outside or inside, or even what continent their on for that matter. They just respond to the growing conditions they are given to grow in. These growing conditions include not just the amount of light, but also the type of light.
This may be the best argument that soil grown plant growers have, because natural sun is better than any artificial lighting out their. And plant photosynthesis is affected by light (as well as other conditions like humidity and temperature) and is a big factor in healthy plant growth. But if you grow outside in natural light like I do, you can through "natural vs artificial lighting" arguments out the window. Of coarse that's assuming all other aspects of the growing conditions are exactly the same, and that's virtually imposable to do. Well unless you have devised a system that mimics the exact outside conditions minute for minute in an inside grow that's using only artificial
lights to compare. Growing outside has the drawback of being exposed to the elements, unless you grow inside a clear greenhouse that allows the natural light in but still allows you to control the environment (I don't yet).
But again it's about the growing conditions like, light, available nutrients, as well as the balance of those nutrients, pH, temperature (both at the roots and leaves), humidity, CO2 availability in the air, oxygen availability to both the roots as well as leaves etc.. If you change one aspect, every aspect of the plants growth and
nutrient uptake (that builds plant tissue) is affected. Plant growth and the building blocks for plant tissue on a molecular level is extremely complex. All of witch will affect the the vitamins and minerals that are in the plant tissue. Again the plant doesn't know if it's in a hydro system or in soil, it's just responding to the growing conditions that it's given to grow in.
Another aspect to plant health is the roots. The plants are only as good as the roots, if the roots themselves are not healthy, the plant wont be healthy (and affect the vitamin and minerals in the plant tissue). There are any number of soil born pathogens, fungi, pests etc. that can compromise the roots. In a hydro system they are much easier to keep out of the system in the first place, simply by not introducing soil plants into a hydro system. But that's not the only way they can get into a hydro system, and if they do get into a hydro system they will spread much faster than in soil. They all can make their way into a hydro system through the water supply, air, animals and insects, as well as dirty tools. But again that's all about the actual growing conditions and not soil vs hydro.
In order to compare you would need to be able to mimic the exact conditions to actually compare results. Both for the roots and foliage, and to mimic soil conditions exactly in a hydro system would be imposable. Not just analyzing the soil so you could duplicate it in a hydroponic nutrient solution in the first place, but soil nutrient levels change as the beneficial micro organisms, acids, and fungi break down the organic mater. The nutrient concentrations in soil change and can be different throughout every square inch of soil (as well as pH levels) on a day to day basis. I won't even get into the differences between field grown crops and hydro with respect to water quality, but suffice it to say what farmer filters his water supply for field grown crops.
Bottom line, it's about the exact growing conditions, not weather it's in soil or hydro. There's no doubt that you can grow good healthy plants in soil. But as for the question of soil grown plants having more vitamin and minerals. Well, you can grow
unhealthy plants in soil as well as hydro, it's about the growing conditions given to the plant, and not weather it's in soil or hydro. If you want to compare a unhealthy hydroponically grown plant to a healthy soil grown plant, yes the soil grown plant will have better plant tissue. You can also compare the other way around and the hydro plant will have better plant tissue.
Bottom line a healthy plant (soil or hydro) will have all the vitamin and minerals it should have (soil or hydro). As for weather hydroponically grown plants have more vitamins and minerals than soil, again it comes down to the growing conditions of the plants being compared. It's just a lot easier to control all the different growing conditions with hydroponics, particularly with respect to the nutrients (and balance of the nutrients) the plants receive. Weather they are given what they need to grow healthy is up to the grower (soil or hydro). Better conditions results in healthier plants, healthier plants results in lots of vitamins and minerals. I don't think you will find any scientist that will tell you "healthier" plants lack anything (at least with a straight face).
Clams of soil grown plants having more vitamin and minerals than hydroponically grown plants are typically spread by soil farmers that want to justify growing in soil, rather than taking on the expense of building a greenhouse and hydroponic setups. But the clams aren't substantiated by any real "CREDITABLE" study's. These clams are also often spread by people reiterating what they read somewhere on the internet without checking out the source of the information, and/or how the study was conducted in the first place. Those are the details that make the difference in understanding what, how, and why there is any difference in plant tissue.
P.S. I haven't even mentioned that different variety's, as well as hybrids of the same type of plant will have a impact on both the environmental conditions the plant needs to be healthy, but also how the plant tissue responds to these conditions. This would also need to be extensively compared in any creditable study.