Bartlett Tree Experts April, 2011
In Chicago, Bartlett Tree Experts are experimenting with applying biochar to benefit urban street trees. They have more detailed information in their company press release:
From the picture it appears that they are drilling holes and side-dressing about 60 existing trees in the Wicker Park/Bucktown community. The application started this year and the study will continue for the next two years.
All trees were aerated with the same number of holes – no matter the treatment.
100% biochar was applied. This was applied by itself, in combination with fertilizer and a fertilizer only treatment was also applied. Control trees only were aerated and immediately backfilled with the soil from the hole. Biochar was applied at a rate of 1/8 pound dry weight per square foot surface area.
from their site: