'black Soil' Has Worked Well For Centuries In The Amazon

[brahmburgers]

In the April 2007 issue of Discover mag, there's an article about the Amazon that relates to Thailand. It talks about new archaeological discoveries showing large native settlements dating back to 9000 B.C. The tropics can sustain small settlements which rely on capturing game, but it’s unusual for a large group of people to settle in the tropics due to soils there are usually very poor and won’t sustain agriculture. The reason being; in the heat and intense rain, organic matter is quickly broken down and used up – therefore precluding the build-up of decent soil. What the archaeologists are finding is the ancient Amazonians had a way of building up soil. The article is deeply detailed, but to put it simply, they mixed charcoal (mainly from burns and pottery making fires) with the soil. They give it the unsurprising name; ‘black soil.’ Thailand is semi-tropical, and farmers here often have to deal with inferior soil. Has anyone tried mixing charcoal with soil – and if so, what’s the scoop? In other words, what’s the method and what results/comments, etc?

On a related note; my hill-tribe worker/friend, who hails from northernmost Laos, makes potting soil the following way: he starts with a wheelbarrow-sized a pile of regular soil. Then he piles a bunch of dry rice stalks on top – as high as possible. He then sets fire to the whole thing. When cool, he mixes it all together. I add some composted manure to it. It works rather well – and has less bothersome weed/grass seeds than the usual potting soil method I use.

[Lickey]

We cleared 12 rai of un-used farmland recently, old potato stalks,brush,prunings from tamarind trees ect, had about 10 huge fires going for several hours, next day this was ploughed in along with about 3tons of sawdust we had near the sawmill with a multi-disc ford, along with all available cowshit from our regular helper.1 month later we planted 700+ banana culms, and soon will be planting 1800/2000 papaya plants, I can still see the large black patches on the field where the fires were, and all bananas there are growing well, I would think this is the same as you describe but on a grander scale, our land is hillside and red soil, {not steep hillside] and im sure has bennefitted by adding Potash to the soil,

Cheers, Lickey..

[Jamie]

What kind of soil do you have there? Is it clayey, or more sand/gravely?

I can see charcoal being a good addition to soil but how much ammendment would it take for say an acre? You are probably talking quite large amounts right? I wonder if you would have to add something else to balance out the basic-ness of potash.

[brahmburgers]

I didn't want to imply that the so-called 'black soi' or 'dark earth' hasn't been practiced in other tropical / semi-tropical regions including Thailand. It just appears that, at various times, it's become a consciously developed method in parts of the Amazon basin. Much of the time, it happened by default merely by slow-burning and allowing nature to cycle the charcoal & soot (scientific name: 'biochar') in to the soil. Besides adding nutrients, it's increases tilth/friability, thereby enabling organisms (insects / worms / beneficial flora, etc) to proliferate - more effectively than compost (though I'm a big fan of compost). Another plus in the big picture is the method fixes carbon in to the soil (where it's useful) and puts a dent in global warming.

To paraphrase from the Discovery mag article: "just substituting 'slash-and-char' for 'slash-and-burn' could reduce human produced carbon emissions in the Amazon by 12 percent." I think when they say 'slash-and-char' - they mean producing charcoal from slow burn - then plowing that in to the soil.

[chownah]

I've been interested in the use of charcoal as a soil amendment for quite some time. It seems to have become popular since the coming of the movement to halt global warming since if carbon (the main thing in charcoal is carbon) could be locked up in the soil then it wouldn't be in the air causing global warming. I've googled around some but never found what I thought was a good reference on the subject and would take a look at any links offered here.

A point that Brahmburgers alludes to is that in discussing this it is important to differentiate between charcoal and ash. If wood or plants or any organic matter is heated without air or oxygen (or insufficient air or oxygen) it doesn't burn but decomposes in a different manner called pyrolysis and the results are gases and charcoal. Charcoal is primarily elemental carbon along with minerals which are not converted to gaseous forms. When charcoal is burned the carbon gets oxidized and leaves in the form of carbon monoxide and/or carbon dioxide and there is a white powder which remains and this is ash...the ash comes from the minerals which do not burn up along with the carbon. If you burn wood (or plants or any organic material) completely you will end up with a white powder too and this is ash too and is made up of the minerals which do not burn away along with the rest of the stuff in the wood. The ash you get from charcoal is mostly the same ash that you would get from the burning of the wood (or plant or any organic material) if you didn't make charcoal of it first.

Ash is minerals and specifically it is usually high in potassium....hence the term "potash"....which is a mineral form of potassium.

To summarize....wood, plant, and all organic material contain minerals...if they are converted to charcoal then their minerals are mostly captured in the charcoal and if charcoal is burned then only the mineral rich ash remains and it is the same minerals that were in the wood, plant, or organic material to begin with and is the same ash (more or less) that would be obtained if the wood, plant, or organic material were burned completely and not converted to charcoal.

It seems from what I've read so far that the benefit of charcoal as a soil amendment is not that it puts more minerals in the soil than the things it is made from would add if left to decompose biologically, but rather in the way that charcoal can hold onto mineral nutrients and keep them from leaching away. I want to point out that many clay soils have this ability (to hold mineral nutrients) too....but I don't know enough about this to know how clay soils compare with charcoal in this.

The Discovery article talked about charcoal build up from pottery making fires. Pottery making fire residues would probably be very rich in ash and probably have comparatively less charcoal. I'm wondering if this is explained in the article...I don't know as I haven't read it and only have read the part reproduced in the original post.

I'm hoping to see some good links here soon!!

Chownah

[chownah]

I found this link:

http://www.agnet.org/library/eb/430/

Its the best thing about charcoal as a soil amendment that I have found so far...take a look. The article covers alot of other bio active type stuff so I'll post this in the unusual fertilizer thread too.

It also indicates that the use of charcoal in the way they discuss is limited due to its high cost.

Edited June 2, 2007 by chownah

[SAP]

In my experiences you can see the immediate effect of potash/charcoal from where ever you have burnt some branches or wood in the field then planted a crop.

But in the day an age of global warming we should be discouraging burning of any materials as you are producing CO2 all the time.

I see on another thread about composting and this is definitley the better way to go to be environmenatlly freindly.

COMPOST

I am no expert but this may help

You can compost any organic material, animals, tree's, weeds, manure everything. It is now big business and alot of research has been done regarding additivies and special microbes, which will speed up the breakdown process. I heard of reports of 2-4 weeks aswell.

Why do you compost and not immediately mix the fresh manure etc into the soil??? During the breakdown process nitrogen in being used, and when you apply the UN-brokendown materail to your soil the Organic matter is stealing nitrogen from the soil to complete the breakdown process and this nitrogen is unavailble to the plant. This effect is referred to the carbon-nitrogen ratio.

I have found the cost of buying truly composted, duck manure, chicken manure etc very expensive in Thailand, I would recommend talking to the local village head or buffalo man and pay him 20 satung per kg of dry shit. Compost this and apply it at about 3 tons per rai. And you will have excellent soil improvement.

If the composting process is done probably all weed seeds can be destroed aswell

BUT surely using CAHRCOAL you are adding to the greeen house effect??

[chownah]

SAP,

One of the advantages touted for using charcoal as a soil additive is that it helps to sequester carbon in the soil instead of letting it escape to the atmosphere. In other words using charcoal on your soil should reduce the green house effect.

Charcoal is almost pure carbon. In making charcoal you are in effect extracting the bulk of the carbon from the plant or wood and not burning it. Instead of burning this carbon you have reduced it to its elemental state which is very stable in a typical soil environiment so it decomposes very very slowly and thus effectively sequesters it for evidentally hundreds of years....and evidentally can improve soil quality but I'm not sure if this is true for all soil types nor do I know the amount of improvement for various soil types.

On the other hand making compost is a biological process whose energy is derived from metabolizing the same carbon that could have been made into charcoal. This meatabolizing of the carbon to derive energy creates carbon dioxide which is released into the air creating green house gases. In decomposing any fresh organic debris (including manure) to get total break down to humus requires oxidizing a MINIMUM of 65% of the carbon into carbon dioxide. The remaining 35% of the carbon will then be incorporated into humus in the soil. The humus in the soil will break down further whenever the soil is tilled especially in aerobic conditions...so adding compost to soil that is heavily worked does not sequester very much carbon in the soil for very long as even the humus gets broken down from the continued tillage.

I think that putting charcoal in the soil is definitely better at reducing greenhouse gases than adding compost to the soil....but....what I'm not sure of is the agricultural benefit from adding the charcoal across diverse soil, crop, weather, and farming practice conditions.

Also, it is best to clearly differentiate between burning debris in a hot fire with alot of air (which results in ash, not charcoal or very little) and burning debris in a smoldering fire where air is excluded...it is high temperatures and a lack of air that creates charcoal.

Chownah

[brahmburgers]

Charcoal would sequester carbon in the soil as Chownah mentioned. Perhaps just as important, is its way of improving the tilth of the soil - thereby enabling all types of organisms to thrive. Compost does that also. There are different types of compost. One method I use is to pile up freshly cut grass & weeds - then wet it down (or let it get rained on, depending on the season). Turn the pile every few weeks, and keep wetting it - until it's brown, damp, and a much smaller pile than original. Perhaps that process releases some carbon/gas, but it doesn't worry me. Mix as much as 50/50 of that decomposed grass a.k.a. compost, with soil. It will aerate the soil. charcoal will also. Charcoal and grass compost both appear to be very good to build good soil enhancers. The mixing methods apply more to potting soil or small plots - and are obviously less practical for a filed crop or orchard.

[Joe Walshe]

My wife's farm is in Esarn and the locals historically burn the rice husks at end of season. We got advice from Organic experts and started ploughing the rice stalks into the ground. The result after many years is a more textured soil with insects and richer in organic matter. Our rice fields also seem more productive. I think this might be the way to go.