[Terrapreta] Indigenous burning

[Tom Miles]

Zane,

 

Having burned thousands of acres of cultivated grassland I can tell you that
the amount of unburned carbon left on the field after burning the straw is
relatively small. As the straw burns the carbon is well consumed. Part of
the inorganic (ash) nutrients volatilize and condense to become submicron
particles which carry off with the smoke plume. A larger part forms large
particles and settles out within a few hundred feet of the fire. So the
carbon is largely converted to CO2 or smoke, which is a combination of ash
and products of incomplete combustion.

 

Some of the studies on the terra preta site indicate that it would take
carbonizing, not burning, the residue from several years of cultivation to
have a significant effect. In Iowa we have been burning switchgrass, a
native prairie grass, as fuel in an industrial boiler.
http://www.iowaswitchgrass.com/ Our experience in Iowa has shown that a
native prairie grass like switchgrass will have about 4-6 tons of removable
straw per acre and another 1.5 to 2 tons in the form of stubble for a total
of 6-8 tons per acre. If you carbonize the removable 6 tons in a controlled
process it will yield about 25% char or about 1.5 tons per acre (75 lb/1000
ft2). If you burn 8 tons of straw on the field in an open fire you will have
less than 5% ash remaining or 800 lbs/acre (20 lbs/1000 ft2). Most of the
ash will be inorganic, not carbon. Even so the yield is very low (20 lb/1000
ft2) compared with the carbon rates necessary for terra preta. Rates of
200-2000 lb/1000 ft2 (4-40 tons/acre) have been discussed here. Prairie
fires were probably also random so the same spot wouldn't be burned
repeatedly.

 

Tom Miles

 

 

       

 

 

  _____  

From: terrapreta-bounces at bioenergylists.org
[mailto:terrapreta-bounces at bioenergylists.org] On Behalf Of Zane Lewis
Sent: Sunday, February 18, 2007 8:27 AM
To: terrapreta at bioenergylists.org
Subject: [Terrapreta] Indigenous burning

 

Hello

I have been wondering if the yearly burnings of the North American prairies
for thousands of years have added fertility to the soil.  Why did this not
create an Amazonian like dark soil?

Zane

-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/terrapreta_bioenergylists.org/attachments/20070218/6593cc00/attachment.html