Followup of Heathers announcement of WSU conference on herbicide contamination readers might be interested in this poster I prepared for a conference last year.
In the experiment I was comparing biochar from a known sources to grosafe, a commercial type of activated carbon used to clean up pesticide spills. So far I have tried with several types of preemergent herbicides and all work well.
Also very interesting to me is evidence that biochar and AC deactivates naturally occurring growth inhibitors that are very widespread in most soils. These materials are released by plants to control growth around their perimeter. They are called allelopathic compounds. Released by sunflower, aster family, walnut, reed canary grass and many others. In Ponderosa pine forest researchers have noticed after a fire charcoal remaining inactivates these compounds and certain grasses and understory shrubs appear whose seed have been kept dormant.
Here is flickr link to my poster
here is link to a larger scale version of same poster. Scroll to the images in the control group on left.
Notice the biochar on left,and AC on right are considerably larger than untreated. This shows deactivation of natural compounds found in this sterile peat/perlite mix.