Situated on a small rural property at Macclesfield in the Adelaide Hills of South Australia, I use local feedstock to produce superior biochar for the use of home gardeners.
I have done many experiments in my own vegetable garden, from raised beds with varying percentages of char (about 35% is my preferred ratio), to large pots with 65% biochar for trees. Many of these experiments are recorded on my facebook page; SA Biochar Works by Greg Marlu
It is fair to say that many of the benefits of biochar are due to its physical presence. What I mean by that is if you are adding it for water holding say, it will change the existing soil in proportion to how much you add.