Science Forums 2

[davidgmills]

Hello all. I have recently learned about terra preta. I am a lawyer so only marginally good at science although I have a father and brother who are both PhD's in biochemistry. I also have three uncles that are farmers (2 dairy 1 beef). My father was always darn good with a garden.

Terra preta has got me interested in gardening again after about a ten year hiatus. I am an internet nut so once I stumbled upon an article on the net about terra preta I poured over every article I could find. Erich is quite a prolific poster.

Anyway I started my terra preta garden back in early November using store bought charcoal briquettes because I didn't know any better. Soon I found out that making your own produced a much better charcoal. But I must say even the store bought briquettes made an difference in the soil's ability to hold moisture.

Over Thanksgiving I began experimenting making my own. It is actually quite easy. I had a two and a half gallon popcorn can with a lid. So I began experimenting in making charcoal with it using sticks and dead tree limbs from the yard. After a couple of times of trial and error, I discovered that the best and most efficient means of making charcoal was to put about two inches of twigs and leaves in the bottom of the can with paper for a starter. Once the fire got going really good and hot I began to put good sized chunks of wood on top of the fire, smoldering it of course, and slowly filled up the can with fist sized chunks of wood. I put the lid on top leaving about a half inch gap. Presto about two hours later, it all turns to charcoal, approximately 1/4 to 1/3 of the size of wood I started with. Very efficient process. Hardly any wood is wasted as starter fuel.

What they say is true about the smoke. First, off comes a gray smoke burning off the water. Then comes a yellowed smoke as the first gases burn off. Finally a blue smoke as the final gases come off. Then no smoke and its charcoal.

Obviously, a two and a half gallon bucket will not produce enough charcoal for a residential garden. So I am going to move up to a galvanized garbage can.

But even after a few weeks I can see the difference the charcoal makes even without the bacteria and fungal growth. The soil is much damper and it seems to really break up clods of clay. Shoveling a full depth of the shovel blade is now very easy, whereas before, it got difficult about half blade depth. Also threw in broken pottery.

Trying to get the garden ready for spring planting. I hope by charcoaling now maybe I will get some bacterial action before spring.

I live in Memphis where we have good soil, good moisture, and a fairly temperate climate.

In thinking about how to make terra pretta for a farm, based on my experience with the charcoal I have made, I would get a big round horse water trough (10 feet or so in diameter and 3 to 4 feet high) and use it. Use some corrugated tin for a cover and take it to the place where you want to start your terra preta plot and make the charcoal on the spot. It really is very safe and as easy to control the fire as a barbecue pit. Start with a hot fire in the bottom of the horse trough. Once it is going good enough that you won't entirely put it out by putting logs on top, start putting them on. Pile them on until you fill the trough up, making sure that the thing keeps smoldering. This might take a couple of days to turn to charcoal, especially if you are using good sized logs. But I feel pretty sure it would work as this is very similar to how charcoal is made in England.

Glad to be a member of this forum.