Well, one thing the speaker totally missed out on, algae is not induced anymore from water column dosing than not.
Where is my algae if what he claims is true?
All substrates have some nutrient content, flux in/out of the substrate the higher concentration in the water column flows right down and into the roots as well as the foliar uptake, adding ferts to the water column allows you to measure and anticipate the levels.
Dirt works. I sure don't think it's the the greatest by any means, I also do not agree just adding it right away, you should soak it good for 2-3 weeks or boil it prior for 15 minutes or so. That and adding lots of plants from the start will ensure success.
“Rooted aquatic plants grow best on a mineral soil such as a silt loam with low organic matter. Rooted aquatic plants require no N, P, S, or micronutrients in the water column when grown on a fertile substrate."
Yea, but the plants grow better when you do and there's ample research to support that aquatic plants generally willt ake from the water column first given a choice. Even when roots were cut off, the plants had the same growth rate. I can make the same claim about fertilizing the water column, aquatic plants require no substrate ferts either if I fertilize the water column.
In general, it's not a bad idea to have nutrients in both locations and some in the substrate as a back up.
But using soil is hardly new........ and the nutrients most certainly leech out of the substrate a couple of ways no matter what you might think, and certainly more than enough to supply algae. Plant's leak quite a bit of nutrients, both from the roots and from the leaves.
As far as no fertilizer at all being added, folks, what is fish food/waste?
In non CO2 tanks, the rate of uptake and growth is slow, if you add CO2, increase growth rates...........of course you'd predict and expect and would find an increase in uptake of NO3, PO4, Fe etc.......then fish waste alone is simply not going to cut it..........and root uptake alone has it's limitations.
But for lower light tanks, non CO2 methods, soil is fine. A few use it in moderate light tanks, I fine it messy, and perfer other products but if you are careful, it can be used, also plain old ground peat works over the long term also.
"Is anyone aware of any resource that explains which roots can obtain adequate nutrition from the substrate, as opposed to ones that REQUIRE to absorb nutrients through their stems/leaves from the water column?"
Well, plants do both, so get use to it
As far as ability to get of the nutrients from one location, that's not realitistic, plants always get from both locations unless you have very specific lab set ups to isolate the water column and the substrate.
Ca/Mg/N/P/K/traces all come in from the fish waste/water changes, plants that decay(leaves etc) and get mineralized.
The real issue here is for what type of growth rates are you interested in and how much light you want to place in the tank and if you want to use CO2 or not.
For a specific growth rate, light, CO2 level the answer can go either way here regarding nutrients since these drive the system as well as fish feeding etc.