Another question or 2 from someone still learning, and I apologize in advance if this has already been covered!
Is it pointless to have a substrate for plant growth for plants that only soak up their nutrients from dosing ferts in the water (if there are those such plants)? I've read that some swords for example either need nutrient rich substrate or tabs because that is how they get their nutrients, but some other plants get their nutrients from the water column?? Is this correct?
For example, if I use Flourite under the sand in my substrate but maybe no plants that get their nutrients primarily from their roots, is the Flourite even beneficial to the aquarium? Does the Flourite and/or other soil release any kind of nutrients into the water column?
Do most/all plants get their nutrients from roots and the water both or just one or the other? If there is a difference, is there an article/list/site I can find out which plants are which as far as how they get their nutritients?
I'm mostly wondering for future reference when we get yet another tank whether it would be worth it to invest in something like Eco, Flourite sand or some other soil for all plants or if it only benefits depending on which plants are wanted.
Geez, hope that all made sense.
These are all very good questions and I am still experimenting with different setups to conclusively confirm one way or another.
Tom Barr has grown plants for years in just about all kinds of condtions and substrates imaginable. He confirms that plants do best when they can access nutrients through the roots as well as the water column. So, to answer your question, having a rich substrate combined with water column fertilization should certainly be more beneficial than just having one or the other assuming that all other factors are conducive to plant growth- sufficent co2(after experimenting I am convinced that pressurized c02 is your best bet rather than DIY c02), good plant density, and appropriate lighting - 3watts per gallon is the yardstick, but you could probably get away with 2watts per gallon, which would probably give you greater protection against algae outbreaks, and appropriate water column fertilization(I suggest Estimative Index but you may have to play around with the suggested frequency, amount or duration to get the right balance depending on other factors: amount of c02, lighting, and plant density).
Now having said that most people grow plants quite well in substrates such as fluorite, eco-complete, soil master select, schultz aquatic soil, and even plain sand and gravel. Keep in mind that just because a substrate manufacturer claims that a substrate is rich in nutrients does not mean that those nutrients are unlocked and necessarily bioavailable to plants. The only exception to this is ADA Aquasoil, and this may account for why many people, including myself, who have grown plants in other substrates, find that ADA Aquasoil gives them the best results. ADA Aquasoil is not without problems, but if you properly setup a tank with it and have patience, IME the results are certainly worth it vs fluorite or SAS.
The other thing, which I am currently testing is whether plant growth tends to be better where methods are used to make nutrients easily accessible to plant roots. Besides using Aquasoil, the only other cheaper option that I can think of and am testing is to wrap root or fert tabs in a towel, and break them into small pieces. The small pieces would then be evenly spread over the first thin sprinkling of peat and positioned closest to the heavy rooting feeders to allow them easy accessiblity to the nutrients from the tabs. That layer would then be capped with a thick layer of regular substrate(fluorite, laterite, sand, etc.,) I am testing this with water column fertilization to see how well this works. Leonardite added to a substrate is something else that I am also testing as Leonardite is alleged to unlock nutrients in substrates and make them more bioavailable to plants. Too early to say, but I will have a better idea after 6+ months.