I came across an article the other day on wikipedia about Terra preta. Has anyone used charcoal like this to enhance sandy soil, like we have in Florida? Does this really work, and what is the best method for applying it?
I don't use biochar, but I'm interested in its uses and have been doing some research for some time. It does appear to have beneficial effects on plants grown in soil amended with biochar, but it's not a silver bullet.
Biochar is very low in nutrients, and if you apply it to the soil it can potentially draw nutrients away from plants. It is better to combine it with compost, manure, or some other source of nutrients.
This paper from the International Biochar Initiative describes some best practices for soil application, including discussion of:
Terra preta appears to be a bit of a mystery still, but there is a ton of literature on biochar available. (Do some googling, look at the references in the paper linked above, or check out the references in the wikipedia article on biochar.)
First, I have not personally used charcoal as a soil amendment.
Where and in what form would you be getting the charcoal?
Charcoal is highly alkaline, therefore unless a soil test report states you need to raise the alkalinity of your soil (and by what recommended amount), I would not add in such a highly alkaline amendment, doing so could very well have a huge detrimental effect on your landscape.
Generally speaking the best way to improve sandy soil is:
The more organic matter you can incorporate into your sandy the soil, the better.
Additional after thoughts & having re-read the linked to, "Terra preta" article
My thoughts on the above 3 points:
I use Charcoal as an amendment. I had a buddy that was doing soil research on Terra preta. I was interested and decided give it a try.
In my case I have a large Rubbermaid tub. On the edge of our property is a compost for lawn cuttings, been there for many years. I filled the tub about 1/2 full with it, sieved out the larger stuff, and added a bunch of worms. I couldn't use the same type of worm as they suspect in nature. But the normal red wiggler compost worms work.
Every few months I change the carbon in my aquarium filters, and during the summer I have a little kiln I made out of a can I use when we have campfires.
I grind up the charcoal and feed the worms like you would for compost.
I use this in pots and in my aquariums. When it's time to plant something I use as much as I need of the charcoal vermipost and mix with as much haydite as I need for the proper body. When a pot is done I mix the used soil back into the tub.
This seems to work because the worms are processing the ground charcoal (activated carbon) the same way or along with the normal soil as the compost what you feed them. Secondly, the Haydite ( an expanded shale product) not only has a similar function as the carbon for small particles, but the larger bits serve to hold a lot of space for air and beneficial bacteria to grow.
They find a lot of busted up pottery in the Terra preta soils. Enough above average to be sure that it was busted up and put there. They think that the worm process, the carbon, and the pottery bits all work together.
I find that in the past year or so that I have been using this I have seen at lest double the growth in my aquarium and slightly more then that with some transplanted houseplants. This spring I intent to try a raised bed with it to see how it fairs.
Anyway, that's my two cents ymmv