They used soil ranging from topsoil mixed with peat or composted manure, a mix with a lot of organic matter, to subsoil having very little organic matter. Usually they put gravel on top of the soil. See the El Natural forum for lots of discussions about soil use. Also see the Science of Aquatic Substrates forum.
There is no doubt that 'fancy' substrates do provide some benefits to plants, but are by no means, a 'must have' to grow them. Since most plants acquire their nutrients via the water column, you can grow them in most substrates as long as the grains are small enough to maintain them rooted. You can always use root tabs on an 'as needed' basis.
If you do a search for 'kitty litter' you will find that it has been used as a base, much like laterite, at a fraction of the cost. Heck, there are beautifully planted tanks using pool sand as substrate. Don't sweat it! :wink:
I use river silt that I dug up just above the water line of the American River, mixed with Soilmaster and topped with more Soilmaster. It has proven to be a very good substrate, judging by my success with the plants. It is certainly a lot cheaper than ADA Aquasoil.
Several months ago Tom Barr did some comparisons of aquatic plant growth using a few different substrates, including Aquasoil, SMS, river silt, and ordinary quartz sand (as I recall). The surprise was how well the SMS performed, and how well the river silt performed, all in comparison to Aquasoil. This was with only one or two plant species, so the results were only suggestive. Again, as I recall, he concluded from this that having a nutrient rich substrate was definitely beneficial, but there were ways other than Aquasoil to get such a substrate. I began using my river silt as a result of this test.
I have used small pebbled river rock for the last 20 years and I have several beautiful tanks with thriving, healthy plants. It is very cheap, and easy to acquire. Just go to any Home Depot or Lowes and pick out what you need.
I've used several different substrates and they all work. Turface and pool filter sand are probably the two cheapest ways to go. For both of these, I added some laterite and root tabs and the plants grow just fine.
I too have used a ton of different substrates with great results. From small pebbles to full laterite to the layer ideas of Amano's earlier products. I have always used root tabs so I don't think I have had a huge difference in growth.