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Fw: [fuelcell-energy] Soil's a natural for storing CO2

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  • P. Neuman self only
    ... From: janson2997 To: fuelcell-energy@yahoogroups.com Date: Mon, 05 Jul 2004 08:15:21 -0000 Subject: [fuelcell-energy] Soil s a
    Message 1 of 1 , Jul 5, 2004
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      From: "janson2997" <janson1997@...>
      To: fuelcell-energy@yahoogroups.com
      Date: Mon, 05 Jul 2004 08:15:21 -0000
      Subject: [fuelcell-energy] Soil's a natural for storing CO2
      Message-ID: <ccb2mp+dkst@egroups.com>

      Soil's a natural for storing CO2

      In a field outside Charleston, S.C., PNNL's Jim Amonette and his
      colleagues from the U.S. Forest Service and Oak Ridge National
      Laboratory have planted 72 pots with Sudan grass. They don't care
      much about the grass, however´┐Żit's the soil beneath that captures
      their attention.

      The pots contain controlled mixtures of soil and additives, there to
      promote the conversion of carbon in plant residues to a more stable
      form known as humus. If the tactic works, Amonette will have found a
      promising way to tackle two problems at the same time: carbon
      depletion from soils and the relentless build-up of the greenhouse
      gas carbon dioxide in the atmosphere.

      "Globally, soils contain four times as much carbon as the atmosphere,
      and half of the soil carbon is in the form of humus," said Amonette,
      a PNNL senior research scientist.

      Until about 30 years ago, soil tillage released more carbon dioxide
      to the atmosphere than burning of fossil fuels. Tillage is
      responsible for the loss of as much as a third of the carbon
      originally present in soils before they were used for agriculture.

      "These carbon-depleted soils are a tremendous potential reservoir for
      carbon that can help slow the increase in atmospheric carbon
      dioxide," Amonette said. "About a ton of carbon is added to an acre
      of a typical agricultural soil every year in the form of crop
      residues. Today, 99 percent of it comes out the top as carbon dioxide
      due to microbial processes. If we can increase the fraction that is
      retained in soil by even a small amount, it will make a huge

      Amonette's fieldwork is an extension of promising work in the lab,
      where his team has been able to promote a soil's natural ability to
      store carbon as humus (i.e., humification) by increasing the soil's
      alkalinity and the frequency of its wetting and drying cycles.

      In the humification process, a common soil enzyme, tyrosinase,
      increases the reaction rate between oxygen and chemicals that are so-
      called humus precursors to form a class of compounds called quinones.
      The quinones further react with amino acids released by soil microbes
      to form humic polymers, complex and durable molecules that are
      crucial to a soil's ability to retain carbon.

      "Because humic polymers are less easily degraded by microbes than the
      precursor molecules," Amonette said, "they survive to diffuse into
      small pores in soil aggregates where they are stabilized for decades,
      if not centuries."

      The humification rate depends on many factors: enzyme stability,
      moisture, alkalinity, oxygen availability, microbial population and
      the physical roperties of different soils. Amonette's experiments are
      designed to weigh the importance of these many factors and to learn
      ways they might be manipulated to increase humification.

      These experiments have shown that soil additives, such as fly ash, an
      alkaline porous byproduct of coal combustion, can promote
      humification. "Fly ash with a high unburned carbon content seems to
      be the best material, and this is fortunate as it has no other use
      and would otherwise be buried in a landfill," he notes.

      By the end of the summer, Amonette hopes to have a handle on how his
      soil preparations play out in the less cooperative real world, where
      such things as humidity (considerably higher in the South) and the
      wetting and drying cycles that help promote humification are far less
      controllable and predictable.

      The soil carbon cycle shows the sources and sinks for atmospheric
      carbon dioxide, with an emphasis on the two-stage process of
      humification. Additives, such as fly ash, help catalyze the process.



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