About three years back I set up my first biochar test bed. I divided the bed into three sections of 10% charcoal, 5% charcoal and 0% charcoal. The sections were all treated the same, except the 0% section was amended with a small amount of wood ash in an attempt to approximate the amount that would have been added incidentally with the charcoal. I even dug the 0% section exactly the same as the 5 and 10% sections.
The first year the char sections of the bed performed poorly. Lettuce failed to thrive in the char sections, but did fine in the 0% section because the charcoal sapped the soil of nitrogen and who knows what else. several growing seasons later though, it's a different story. I forgot to mention in my leek planting video that the bed I used was this test bed. now that the leeks are established and growing, there is an obvious difference in the three sections with the 10% doing the best and 0% by far the worst. While there could be some other factors involved, it's pretty clear that the charcoal is having a very positive effect. I would say that the 10% section could be doing as much as 600% better than the 0% section. The weeds look a lot happier too.
What the exact effect is, I don't know, and while I'd like to know, I don't necessarily need to. It is just working and that is the important thing. It seems that the charcoal amended sections are making better use of whatever resources are put on them. We'll see how the leeks progress through the season.
What I learned from this experiment so far is that 10% is better than 5% and 10 inches deep makes a difference. I'd like to put in a similar experiment with 10%, 15% and 20%. I'd also like to do sections of a bed at a constant percentage, but one dug to 2 feet and one dug to only 12 inches. And there are many more experiments I could do. Each bed I install will be a different test of some kind. It is easy enough to set them up and I could potentially learn from them for years. I hope some of you out there will start collecting or making charcoal and setting up your own experiments. If you already are, leave a comment and tell us about it.