Terra Preta is an elusive substance that "magically" transforms poor, depleted, or dead soils into everlasting, robust, fertile, "super soils" that will grow anything at twice the regular yield!!!!!!!
Yeah, right!
No one truly knows what the exact mechanisms are that allow Amazonian soils to be transformed from some of the poorest soils on the planet to some of the most fertile. One theory is centuries of spreading burned trash on fields has:
- Built up sufficient carbon black (bio char, charcoal) to effectively halt rain water nutrient leaching.
- Added large amounts of additional nutrients.
- Provided an environment for high levels of microbial activity.
- Through A), B) and C) allows the soil to be productive for centuries.
- Drastically reduced watering needs are.
Since we've established we don't have centuries to burn all our trash and spread it on our fields, the trick would seem to be to make a soil amendment as close as possible to the observed characteristics of the "terra preta" soils. To whit:
Make a diverse low-temperature charcoaled product, inoculate it with a good starter microbial soup, and then mix it into your top soil or garden.There aren't that many good, controlled scientific studies for the method I'm suggesting, but here are some of the results you might expect:
- Increase in yields 10% to 100%
- Water requirements reduced up to 50%
- Stabilizing of soil moisture
- Less pests, deters snails, ants
- No need for chemical fertilizers
- Organic fertilizers (compost) won't leach, so will benefit several seasons (probably decades)
- Soil shouldn't hard pan or crust
- Microbes now have a "happy" home in the nooks of the bio char
- (see also: Gardening with Biochar FAQ below)
You want more info? Google "terra preta" ;)
Also included is a recipe for a terra preta equivalent, which, while it won't have all the 'goodness' of a true terra preta, should give you most of the important benefits.
How to Make True Terra Preta (Backyard / Small Scale)
Materials list:- 1, 55 Gallon Barrel with air holes close to bottom (Larger)
- 1, 55 Gallon Barrel that will hold water without leaking (Slurry)
- 1, 20+ Gallon Barrel that will hold water without leaking, with lid (Smaller)
- Some Bricks
- Fire wood
- ~3 Gallons Compost Tea
- ~1 Cups Molasses (most any organic sugar source)
- Clean water (Rain, Reverse Osmosis, or Distilled is best. Let tap water sit for 24 hours prior to use and don't use tap water at all if it has fluoride)
- Enough dried material to fill the smaller barrel
For best Terra Preta include any and all Organic matter you can find. Grasses, prunings, leaf litter, acorns, nut shells, bones, corks, coconut husks, corn cobs, any plant matter or waste food. The more variety the better, just make sure it's dried and isn't too fatty or oilily.First put the smaller barrel on enough bricks that you can place the larger barrel upside down over the smaller barrel such that there is enough of a gap between the larger barrel and the ground so you can turn both barrels over without spilling the smaller barrels contents.
After placing the smaller barrel on bricks, fill it with the material you're turning into Terra Preta, put it's lid on, and place the larger barrel upside down over it. Flip both barrels over and fill the gap between the smaller barrel and larger barrel with fire wood.
(For better details follow the first two steps of a two-barrel charcoal retort. He's using a much smaller barrel system, so come back here when you get to "Light it" at the beginning of step three. Click "Back to the picture page" to see pictures.)
Light, keep adding wood for about 2 hours then let burn out. (Cooking a meal or three is optional.)
Let cool overnight.
Crush biochar and ash remnants to 3/4 inch pieces or smaller. The size is somewhat dependent on your usage. If you're adding it to something outdoors 3/4 inch and smaller should be fine. If you're adding it to potted plants, I'd go for about the size of small pebbles.
Add cooled biochar (smaller barrel) and ash from the larger barrel to the second 55 gallon drum (Slurry barrel). Stir to verify contents are below approximately 100° Fahrenheit (38°C), otherwise you'll kill the good bugs in the compost tea. Add the compost tea and molasses. Stir in enough water to make a soft slurry. Cover (plywood, original barrel lid, etc.) to keep bugs out and place in a warmish (70+F) place. Stir once a day and let the tea inoculate the biochar for about a week.
Drain the slurry (and capture the liquid for use as the next batch's starter or as a liquid fertilizer).
Additional Notes:
The smaller barrel can be anything that will hold water without leaking and has a lid tight enough to keep material from spilling out but loose enough to allow gasification products to escape (without blowing up the barrel). By having the smaller barrel upside down all oxygen will be used up and proper charcoaling will take place. Any 20 gallon oil drum, water heater core, welded propane tank(s), old air compressor tank, etc. will work.
How to Make a Terra Preta Equivalent (Small Scale)
Materials list:- 1, 5 Gallon Bucket, with lid
- ~10 lbs crushed hardwood charcoal
- ~1 Gallon Compost Tea
- ~1/4 Cup Molasses (most any organic sugar source)
- Clean water (Rain, Reverse Osmosis, or Distilled is best. Let tap water sit for 24 hours prior to use and don't use tap water at all if it has fluoride)
- Something to stir with (long handled shovel works well)
So far the easiest method I've found to crush charcoal is to place the bag on concrete and drive over it with a heavy truck. If you're doing a large volume, try a chipper / shredder.
Place crushed charcoal, compost tea, and molasses in the bucket and stir. If needed add some water to make a soft slurry. Mix well once a day and let the tea inoculate the charcoal for about a week.
Drain the slurry. Capture the liquid for use as the next batch's starter or as a liquid fertilizer.
Scale up as needed.
Application Rates:
This small study, Effects of Varied Soil Composition (Char, Sand, Potting Mix) on the Growth of Radish Starts, suggests that 1/3 char to 2/3 soil gives the best plant growth results. Up to a 16.67 percent addition of sand (~17% Sand, ~50% Soil, 33% Char) shows a marginal decline from maximum plant growth.The addition of char to achieve 1/3 char of total volume seems to be the key to get best results no matter what the composition of the existing soil.
True Terra Preta and Terra Preta Equivalent
(for recipes see above)
Small Scale
- For plants in pots or individual plants being planted outside, use drained terra preta slurry for approximately 1/3 of the total volume of potting material or fill material. If you made your own slurry, as above, and have no need to keep the drained liquid for any other reason, use its for the plants first watering(s).
- Current Guess for large scale applications: Spread 3 inches of drained terra preta slurry on ground and till in to six inches of top soil. If you have the material, I'd SWAG that you could spread slurry up to 50% of your original soil depth. (e.g. spread 6 inches for 12 inches of top soil if your plow / tiller will mix a full 18 inches. Your result is then 1/3 terra preta by volume.)
A less labor intensive method that should give similar, but not as good, results would be to spread X inches of crushed charcoal, spray it with a compost tea solution, and then till it in. Again, don't just dump charcoal on a field and expect good results.
These suggestions were found on the web. If the labor is costlier than the bio char and tea, then you're probably better off overdosing so you don't have to do another application.
Small Scale
-
- Bio Char: 1/2 pound per square foot.
- Compost Tea: 1/2 ounce per square foot.
- Low End:
- Bio Char: ~2 tons per acre, ~5 mt/ha, .1 pounds per square foot.
- Compost Tea: 5 gallons per acre.
- Bio Char: ~10 tons per acre, ~20 mt/ha, .4 pounds per square foot.
- Compost Tea: 15 gallons per acre.
Simplistically, activated charcoal is highly porous charcoal, so you would need less to achieve the same results? So far I haven't found any information one way or another.
If you can get steam activated charcoal for the same price as charcoal, go for it.
- ????
Sources:
Bulk Lump CharcoalAt Restaurant Depots / Supply firms, 20 lbs bags are under $10.
Possible source(s) for buying 1 ton or more (FOB)
B&B Charcoal Products
Possible source(s) for buying 20 tons or more
Activated Carbon; Pure Organic Fertilizer, Hardwood Charcoal; Activated Bleaching Earth
Minimum Order Quantity: 20 Tons, FOB surabaya USD 300~1,000
Compost Tea
Microbial Earth: $7 for 1 gallon at the downtown Austin Farmer's Market on Saturday mornings.
Natural Gardner: Call first they don't always have it ready.
Great Outdoors: Call first they don't always have it for sale.
Reference Information:
- Gardening with Biochar FAQ
- 1 U.S. ton per acre = 2.24 metric tons per hectare. /
- One acre = 4,840 square yards = 43,560 square feet