Has anyone heard of lignite coal being used as a soil aditive to increase humas and carbon in soil?I guess it could be true because lignite is one step above being peat.
Lignite Coal
Have you ever seen lignite? A good portion of our ranch has it under the top soil. At the bottom of the knoll by the front gate it is close enough to the surface that it was brought to the surface when we were boring holes for a cross fence. Dry, it is rock hard. It's difficult to describe what it's like when wet. It's not slimy like clay, but neither does it crumble. It does make a good water filter. Our well water is very clean and clear.
Could biochar be what you are thinking of? http://davesgarden.com/community/forums/t/947897/
read about "terra preta".
Biochar is utilizing ancient farming practices.