I'm not a believer in incorporating any organic material under the soil surface, or disturbing the soil for any reason besides adding a plant, or removing an unwanted plant. The decomposition crew will take care of decomposing whatever OM that is placed on the surface, distributing it's components to the proper level under the surface, and making the nutrients available to roots. This is how mother nature distributes OM naturally, on the surface. I try to keep a constant layer of OM on the surface, added whenever various materials become available. The wider the variety, the better.
http://permaculturenews.org/20...
