I anyone aware of projects that have combined biochar with other types of soil
amendment to improve farming in the drylands ?

I am thinking of examples like TerraCottem:
http://www.terracottem.com/pages/en/home.htm
Perhaps there is a limit to the benefits, as there might be some overlap in the
properties of the materials, especially with regards to moisture retention.
Still, it's worth checking out.

Related Blog: http://desertification.wordpress.com/