[Terrapreta] Praire is natures way of making terra preta.

[Tom Miles]

Where is the data?

 

Before you jump to too many conclusions someone should do a full literature
search on this topic. I found several references on biochar and prairie
fires when I was doing an internet search a few months ago. I do not have
access to some key academic databases in soil science but I found that there
has been work on prairie fires and the role of the resulting carbon in soil
fertility.  If I remember correctly they concluded that fire stimulated
growth in grasses partly due to thermal shock, partly due to the elimination
of residues and competing grasses, partly due to nutrients in the burned
residue,  and only secondarily due to carbon accumulation. It was calculated
that he amount of carbon from burning contributed little to soil organic
carbon and long term accumulation. The concentration of inorganic elements
that results from burning stimulated growth for the first year but the
effects were not lasting. Similar studies have been done for rice straw.

 

We saw these effects in the 1970s when we burned hundreds of acres using
field burning machines that we designed. We used to burn the residues from
our grass seed harvest In our Willamette Valley. Annual burning of more than
300,000 acres resulted in production of high purity seed and elimination of
volunteer plants and diseases. We designed and tested machines to control
combustion of the residue. We machine burned hundreds of acres on many
different grasses. Fossil fuel was only used to run the tractor and a fan on
the machine, The residue sustained it's own fire. Burnout was good. Char
left on the ground was not measured but it was probably more than open
burning because we released less to the atmosphere. Emissions were very
good. Most of the nutrients returned to the soil rather than put into the
atmosphere. Political pressure changed the regulations and reduced  burning
to less than 10% of the total acreage. It is used sparingly now for select
fields. In some areas more straw is returned to the soil which has improved
tilth and water use. Seed varieties have also changed with the market so we
now grow less annual and more perennial grasses.

 

Tom Miles

         

 

 

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