Personally, I really don't think the idea of nutrients being included in the soil (at least in large enough amounts where you don't need to add to the soil) is a very good idea. I've always had success using plain old dirt for seedlings. Seedlings are very sensitive and all they really need is plenty of light, a temperate space, and adequate water (don't water too much, use your head and eventually you'll gain a feel for it).

One more thing you should definitely be aware of is that once you plant has rooted into soil with included nutrients there is really nothing you can do in the case that it starts to become over-fertilized. Most soils with nutrients included function by water being introduced to soil (in other words when you water, the soil feeds itself as a reaction), which means you can't "flush" the soil of its nutrients like you can when you feed it yourself with seperate nutrients.

If you insist on making use of the soil, I would mix it with regular dirt first (say half and half) to weaken its strength.