No, I've heard of leonardite but don't know much about it. It doesn't appear to be compost, it is derived from lignite coal. I just quickly looked at a few studies that used it and the results seem to be hit and miss depending on the type of plant and also on the amount of leonardite used. There were some benefits with some plants, but when too much is used apparently it can inhibit plant growth.
This was one of the more understandable studies I found:
http://hortsci.ashspublication...
