Doesn't like Kool-Aid
Join Date: Feb 2003
Location: Hawthorne, New Jersey
It would be great if SCMurphy would chime in on this. he has been running soil substrates and probably has the most experience with them.
Personally, I wouldn't skimp on a substrate. It is one of the most important aspects of a planted aquarium. It is the easiest thing to put in initially, but one of, if not the most difficult thing to replace once you have things up and running.
While it might not be the least expensive thing, a good substrate like Flourite or Eco-Complete would probably be the best thing for someone just entering the hobby, just for the reasons Rex mentioned. Soil varies from source to source. It's nutrient contents can vary greatly from package to package. That lack of consistency would make it very hard for even an experience aquarist to maintain stable conditions in the aquarium. For a beginner this could be a great source of frustration as well as discouragement.
Best bet for someone new and on a budget who might not be willing to wait and save up for Eco-Complete or Flourite, would be to use one of the gravel substrates. Some laterite under a finer gravel substrate would more than likely be a good start. Searching through the "Substrate" part of the forum would provide some good substrate suggestions.