Several readers have asked what sort of on-the-ground results we see from our biochar experiments.  Over the last couple of years, I've applied the winter's charcoal (separated from the ashes and activated with urine) to half of various garden beds, keeping notes on the location.  The idea is that I should be able to compare the biochar half to the control half and get some pretty good anecdotal evidence of the changes biochar makes in the soil.

The trouble is that both halves of the beds look the same.  And it occurred to me, as I went out to monitor each one, that biochar's ability to expand the soil microorganism population could carry over into the untreated half of the bed.  Soil fungi can send their hyphae quite a distance through the earth, so maybe the control half of the bed gets similar benefits to the biochar half?

If that hypothesis was correct, I should be comparing the growth of plants in the biochar beds to plants in neighboring beds.  The trouble is that our garden is extremely diverse, and no two beds get the same treatment.  Depending on what's planted there, a bed might get one, two, or three top-dressings of manure per year, or --- if I have some on hand --- the soil may instead benefit from worm compost.  It might get kill mulched with cardboard if it gets too weedy, or might just keep a gentle coat of straw.  I might grow three rounds of buckwheat between spring and fall vegetables, might plant oats or oilseed radishes after summer cucumbers die back, or might plant no cover crops at all.  And, of course, the actual vegetable grown in each bed can affect the soil, with greedy corn depleting many nutrients but kind beans giving some nitrogen back.  This is the reason I'd hoped to do a within-bed trial --- comparing the effects of biochar between beds is nearly impossible.

So, my conclusion is no conclusion.  Biochar either doesn't help, or it does.  (It definitely doesn't seem to hurt.)  Since we have nothing else pressing to do with the waste from our wood stove, I'll keep adding biochar to our soil and maintaining notes on the locations, and maybe I'll see long term effects that aren't visible after a mere year and a half.

How about you?  Do you have solid evidence of the effects of biochar in your garden?  If so, how did you process and apply the charcoal and what was its original source?