There are several processes and lots of research. Pyrolosis is an ancient
process that produces essentially pure carbon (charcoal) and CO and H2 from crop
residue. There are ways to separate the CO and H2, so that the carbon monoxide
is used as  the energy source for the process itself and the hydrogen is the
fuel output.
    The carbon component can be put back in to the soil as a soil amendment. This
is said to have huge advantages over  composting or plowing under that same crop
residue. Research has shown that adding carbon in the form of charcoal to the
soil lasts much longer in the soil (centuries compared to months) so over time
it accumulates. Carbon in that form improves soil fertility by holding K-N-P and
water better. That means the farm needs  less water, fertilizer and energy to
produce the same yield. And carbon in that form has been shown to improve soil
microbial action that benefit plant growth. And for those worried about green
house gasses it significantly reduces the amount of CO2, methane and NO2
emissions that come from farm soil as compared to more traditional methods of
adding back some of the organic matter.
    Think about this: You mow your lawn for decades every week and very little of
that carbon that was removed from the atmosphere and ends up in grass clippings
ends up as carbon in the soil. It is a very inefficient process and it reaches
an equilibrium where the soil is out gassing as much carbon as it takes in.
Most of the carbon decomposes and becomes CO2 or methane and returns back to the
atmosphere. For farm soils that are tilled the amount of carbon retained in the
soil is even less than for soil that is not tilled.

    Both India and China are very serious about this. It has a lot of potential for
small scale agricultural development - for producing rural energy self
sufficiency and for improving worn out soils.

-jim

    Is it your belief that everything you have never heard of is by definition
silly?

    Have you ever heard of a desert. How about a man-made desert? Many of the
world's deserts are man made and the process for turning arable land into desert
is pretty simple - remove the carbon from the soil and you have a desert. There
are very few places in the world that get enough natural regular rainfall to
support any sort plant life without at least .5% carbon in the soil. The places
where the carbon is below that level are now deserts. Once plants stop growing,
the soil carbon quickly drops to close to 0%.

    Typical midwestern US soils in pre-columbia times had around 8-10% carbon and
some soils can be as high as 50% carbon. Typical US cropland today has about
2-4% carbon. That level of carbon depletion has been shown to make a huge
difference in yields. Experimental plots have demonstrated that corn yields of
up to 400 bu/acre are routinely possible on unirrigated land with soil that has
carbon content in the neighborhood of 10%. Essentially that would be like
farming on pure potting soil.
   

    It has been estimated that the total amount of carbon that has been removed by
man (mostly deforestation, farming and grazing) since the beginning of time is
of the same magnitude as the total amount of carbon man that has  burned by
fossil fuel usage.

http://www.eprida.com/invest/index.php4
http://www.geotimes.org/webcasts/article.html?id=char.html
http://www.aes.ucdavis.edu/NewsEvents/News/Impact/impact_15.pdf