[Terrapreta] Terra Preta - not just about charcoal in soil

Sean K. Barry sean.barry at juno.com
Sun Sep 30 15:44:09 EDT 2007


Hello 'terrapreta' List,

I am writing today to this group about what I am learning from reading some more parts of the book "Amazonian Dark Earths: Origin, Properties, Management", edited and compiled by another of our colleagues on this list, Johannes Lehmann.  I believe there are some very crucial understandings that we all need to have, in order to achieve what we want to with "Terra Preta" Nova".

The agricultural miracle that is being sought by forming Terra Preta soils anew, is NOT just about putting charcoal in soil.  Charcoal is a tool, one which allows the concentration and storage of plant nutrients in soil, where they would otherwise be lost to seasonal harvests, run-off, and/or leaching.  It is thought (and being researched for more confirmation) that charcoal in soil can improve the environment for soil microorganisms, because its porous nature retains water and provides a haven for the growth of soil microbes.  Increasing the populations of soil microbes will not occur just because there is charcoal in the soil, however.

Soil microbes need energy to grow.  Then, they can do the chemical breakdown of other matter in soil, making more of the plant nutrients in those materials available to plants growing roots into the soil and shoots above the soil.  Usually microbes get this energy from undigested carbohydrates in and on the soil (soil organic matter).  They also get this energy from carbohydrate exudates that the plants themselves provide to supply the soil microbes with energy they need.  These symbiotic relationships between plants and soil microorganisms are as old as life on land.

The carbon that is in charcoal is NOT a FERTILIZER.  Most charcoals do contain some plant nutrients, though, and these will increase the stock of plant nutrients in soil once fresh charcoal has been put into soil.  This part of charcoal IS A FERTILIZER.  The stock of nutrients in the soil will not increase further, however, as a result of its presence in the soil.  If the soil is used for agricultural purposes, then plant nutrients will deplete as harvests occur, even if the soil contains charcoal.  Making charcoal from those plant wastes that are left after harvest also WILL NOT improve the stock of nutrients.

Making charcoal amendments alone, especially just from the plant wastes that remain in an agricultural field after harvesting WILL NOT improve the fertility of that field.  It may improve the ability of the soil in that field to HOLD ON TO what fertility is does have better, but the nutrients do not just appear.  The nutrients have to be input for the fertility of the soil to be improved.

In the formation by humans of the Amazonian Dark Earths (ADE) (a.k.a Terra Preta soils), what occurred was that the people were able to make inputs of plant nutrients exceed losses.  They were greatly aided in doing this by incorporating charcoal into the soil.  But, it was NOT CHARCOAL ALONE and it was not charcoal from only the plant wastes in their fields that made this increased fertility in ADE soils.

They made native soil into more fertile patches of soil (ADE sites) by incorporating all of these things; their wastes from food production, at harvest and post harvest, human and animal digestion products (night soil and manures), pottery sherds, and charcoal made from plants covering a wider area than where they made Terra Preta soils.  The valuable and necessary aspect of ALL of these inputs into the ADE sites was that they all served to increase the stock of nutrients on the site over time, limit the losses, or retain the stocks of nutrients in the soil.

It is a completely different way of practicing husbandry of the land, that modern agriculture is not focused upon.  Making Terra Preta is about giving more to the land than we take from the land.  It is not just about making it black with charcoal.


Regards,

SKB



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