Personally, I grew a lots of orchids, aroids, houseplants, and vegetables (in containers and hydroponic systems) before I ever maintained a planted aquarium. Coming from a more traditional horticultural background, I assure you that scientific evidence is often at odds with the current practice of commercial and hobbyist plant growers.
One of the best examples of the discord between scientific research and practical application in horticulture (as it applies to hobbyist and commercial growers) is the use of high phosphorous fertilizers. In general, the majority of plant growers, particularly growers perennial flowering plants, believe that high P fertilizers induce flowering and contribute to better overall plant health. However, reports published by the scientific community conclude that ornamental plants do not benefit from phosphorous provided in excess of the 3:1:2 N-P-K ratio (given that nutrients exceed limiting thresholds and environmental conditions are conducive to growth). I used to side with the hard science and therefore the 3:1:2 club, but I was eventually persuaded by a local nursery owner to experiment with 1:2:2 ferts on a few orchids and anthuriums that were giving me trouble. In short, the results were so excellent that I now seldom use 3:1:2 formulations on my terrestrial plants.
I can't provide any hard evidence as to why I've had better results fertilizing with higher P ferts (relative to N and K), but I'd rather go with what my eyes and plants are telling me instead the what's written the science journals.
The same applies to what I see in my aquariums. I was initially very skeptical of the real value of aquasoil given its price and lack of scientific backing. However, I gave it a try after seeing lots of fabulous aquasoil tanks and, given the great firsthand results, I'm now more than happy to pay over $30 for what essentially amounts to a bag of clay and humus. Moreover, the results I've had with other ADA products like power sand and Green Brighty Step 2 have definitely converted me from an ADA skeptic to a believer.
The reality is that the scientific community isn't going to provide much help to planted tank hobbyist until the hobby starts making a lot of people a lot of money; only then would the kind of grant money that attracts the best minds follow. So, given the current paucity of research and my general experience with horticulture, I think most hobbyists should go with what their plants are telling them instead of the Ph.Ds.
The market is always going to be full of snake oils, magic bullets and egregious marketing practices and blogs/forums will always be laden with poor or misconstrued information that's somehow passed off as 'science'.
So basically, trust no one, and use your eyes as well as your head.
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