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Re: The nitrogen problem?

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  • XK SAZ
    ... t his belief was that something like 70% of the nitrogen fixed in humans an= d their livestock had been fixed since the mid-20th century, by the Haber
    Message 1 of 4 , Jul 29, 2004
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      > A friend of mine had pointed out that he wasn't entirely sure about the
      > accuracy of his statistics and couldn't instantly point to a citation, bu=
      t
      > his belief was that something like 70% of the nitrogen fixed in humans an=
      d
      > their livestock had been fixed since the mid-20th century, by the Haber
      > process.

      I'm not sure what "nitrogen fixed in humans" means...
      but I found this.


      Nitrogen molecules occur mainly in air. In water and soils nitrogen can be=
      found in
      nitrates and nitrites. All of these substances are a part of the nitrogen c=
      ycle, whereas there
      are all interconnected.

      Humans have changed natural nitrate and nitrite proportions radically, main=
      ly due to the
      application of nitrate-containing manures. Nitrogen is emitted extensively =
      by industrial
      companies, increasing the nitrate and nitrite supplies in soil and water as=
      a consequence
      of reactions that take place in the nitrogen cycle. Nitrate concentrations =
      in drinking water
      will greatly increase due to this.

      Nitrates and nitrites are known to cause several health effects. These are =
      the
      most common effects:

      - Reactions with haemoglobin in blood, causing the oxygen carrying capacity=
      of the blood
      to decrease (nitrite)
      - Decreased functioning of the thyroid gland (nitrate)
      - Shortages of vitamin A (nitrate)
      - Fashioning of nitrosamines, which are known as one of the most common cau=
      ses of
      cancer (nitrates and nitrites)

      But from a metabolic point of view, nitric oxide (NO) is much more importa=
      nt than
      nitrogen alone. In 1987, Salvador Moncada discovered that this was a vital=
      body
      messenger for relaxing muscles, and today we know that it is involved in t=
      he
      cardiovascular system, the immune system, the central nervous system and t=
      he peripheral
      nervous system. The enzyme that produces nitric oxide, called nitric oxide=
      synthase, is
      abundant in the brain.


      Although nitric oxide is relatively short-lived, it can diffuse through me=
      mbranes to carry
      out its functions. In 1991, a team headed by K.–E.Anderson of Lund Univers=
      ity Hospital,
      Sweden, showed that nitric oxide activates an erection by relaxing the mus=
      cle that
      controls the flow of blood into the penis. The drug Viagra works by releas=
      ing nitric oxide
      to produce the same effect.
    • XK SAZ
      nitrogen cycle, the continuous flow of nitrogen through the biosphere by the processes of nitrogen fixation, ammonification (decay), nitrification, and
      Message 2 of 4 , Jul 29, 2004
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        nitrogen cycle, the continuous flow of nitrogen through the biosphere by the processes of
        nitrogen fixation, ammonification (decay), nitrification, and denitrification. Nitrogen is vital
        to all living matter, both plant and animal; it is an essential constituent of amino acids,
        which form proteins of nucleic acids, and of many other organic materials.

        Nitrogen Fixation

        Although the earth's atmosphere is 78% nitrogen, free gaseous nitrogen cannot be utilized
        by animals or by higher plants. They depend instead on nitrogen that is present in the soil.
        To enter living systems, nitrogen must be "fixed" (combined with oxygen or hydrogen)
        into compounds that plants can utilize, such as nitrates or ammonia. A certain amount of
        atmospheric nitrogen is fixed by lightning and by some cyanobacteria (blue-green algae).
        But the great bulk of nitrogen fixation is performed by soil bacteria of two kinds: those
        that live free in the soil and those that live enclosed in nodules in the roots of certain
        leguminous plants (e.g., alfalfa, peas, beans, clover, soybeans, and peanuts). Among the
        free-living forms are species of Clostridium, discovered c.1893 by Sergei Winogradsky,
        and Azotobacter, discovered c.1901 by M. W. Beijerinck. Both Clostridium and Azotobacter
        are generally present in agricultural soils, and both are saprophytes, i.e., they use the
        energy from decaying organic matter in the soil to fuel soil processes, including nitrogen
        fixation.

        Bacteria that live in the roots of legumes are of the genus Rhizobium, first isolated c.1888
        by Beijerinck. These rod-shaped bacteria enter the roots chiefly through the root hairs and
        then work their way to the inner root tissues. There they stimulate the growth of tumorlike
        nodules. Within the nodules the bacteria develop into forms called bacteroids, which live in
        a symbiotic (mutually beneficial) relationship with the green plant. The bacteroids take
        carbohydrates from the plant for energy to fix nitrogen and synthesize amino acids; the
        plants take the amino acids elaborated in the nodule to build plant tissue. Animals in turn
        consume the plants and convert plant protein into animal protein. Rhizobia can be found
        free-living in the soil, but they cannot fix nitrogen in the free state, nor can the legume
        root fix nitrogen without Rhizobia.

        The exact biochemistry of nitrogen fixation within the nodule is not yet understood. It is
        estimated that more than 300 lbs of nitrogen per acre (340 kg per hectare) can be fixed by
        fields of alfalfa and other legumes. After a harvest legume roots left in the soil decay,
        returning organic nitrogen compounds to the soil for uptake by the next generation of
        plants. For this reason crop rotation in which a leguminous crop is rotated with a
        nonleguminous one is a common practice for maintaining soil fertility.

        Other Aspects of the Nitrogen Cycle

        Decomposing animal remains and animal wastes also return organic nitrogen to the soil as
        ammonia. Many different kinds of decay microorganisms participate in ammonification.
        The nitrifying bacteria of the genus Nitrosomonas oxidize the ammonia to nitrites, and
        Nitrobacter oxidize the nitrites to nitrates. The nitrates can then be taken up again by the
        green plant. The cycle of fixation-decay-nitrification-fixation can proceed indefinitely
        without any nitrogen being returned to a gaseous state. But still another group of
        microorganisms, the denitrifying bacteria, can reduce nitrates all the way to molecular
        nitrogen. Denitrification occurs only in the absence of oxygen and is not common in well-
        cultivated soils.

        Effects of Artificial Fixation

        Nitrogen fixation can also be accomplished artificially by various methods (see nitrogen).
        Humans annually fix vast amounts of nitrogen for industrial purposes and for use as
        fertilizer. Unfortunately, large-scale legume cultivation and artificial fixation may be
        upsetting the natural nitrogen cycle in the biosphere. There is some question whether
        natural denitrification can keep pace with fixation. For one thing, run-off of nitrate
        fertilizer can cause eutrophication of lakes and streams (see water pollution) and can foul
        drinking supplies. Another environmental problem is that inorganic fertilizers tend to
        depress legume fixation. As a consequence, root tissue remaining after harvest is poorer,
        and thus more fertilizer must be applied the following year.
      • XK SAZ
        http://story.news.yahoo.com/news?tmpl=story2&u=/nm/20040803/sc_nm/ environment_deadzone_dc
        Message 3 of 4 , Aug 4, 2004
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