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Nitrogen Fixation by Free-Living Bacteria - explains good results despite assumed N deficit of wood?

 
Dale Hodgins
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Many members have reported surprisingly good results with their plants despite the fact that they have used prodigious quantities of wood chips and other N poor mulches without adding enough manure or other high N components to correct the deficiency. Common wisdom suggests that the addition of these materials should cause long term deficiency. I gleaned this snippet from The Nature Knowledge Project. It turns out that N poor environments favor these bacteria which don't need a N fixing plant to associate with. Notice the last sentence. I wonder if the high carbon content in wood waste also favors these bacteria ?
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Nitrogen Fixation by Free-Living Heterotrophs

Many heterotrophic bacteria live in the soil and fix significant levels of nitrogen without the direct interaction with other organisms. Examples of this type of nitrogen-fixing bacteria include species of Azotobacter, Bacillus, Clostridium, and Klebsiella. As previously noted, these organisms must find their own source of energy, typically by oxidizing organic molecules released by other organisms or from decomposition. There are some free-living organisms that have chemolithotrophic capabilities and can thereby utilize inorganic compounds as a source of energy.

Because nitrogenase can be inhibited by oxygen, free-living organisms behave as anaerobes or microaerophiles while fixing nitrogen. Because of the scarcity of suitable carbon and energy sources for these organisms, their contribution to global nitrogen fixation rates is generally considered minor. However, a recent study in Australia of an intensive wheat rotation farming system demonstrated that free-living microorganisms contributed 20 kilograms per hectare per year to the long-term nitrogen needs of this cropping system (30-50% of the total needs; Vadakattu & Paterson 2006). Maintaining wheat stubble and reduced tillage in this system provided the necessary high-carbon, low-nitrogen environment to optimize activity of the free-living organisms.
 
Paulo Bessa
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Great news.

I always suspect of this.

It is knowledge that many bacteria fix nitrogen without other plants around. And here in Iceland we have newly formed soil (after eruptions) that gets colonized by a few pioneer species that are not legumes or known to fix nitrogen. The first is always lichens and moss, then follows a species of thyme, blueberries, and others.

So either these fix their own nitrogen through a yet unknown mechanism, or the soil has already nitrogen from those independent fixing bacteria.

However in a newly forming island, scientists observed that many other native species only appeared at sites where bird were laying their excrements. So these nitrogen hungry species obtain their nitrogen through more conventional means, showing that elsewhere there was simply not enough nitrogen available for them.



 
Jeff R Hodgins
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The same may be true for pyrolyzed material, due to its low oxogen content and ionic properties.
 
henry stevenson
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Location: Devon, UK
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Ive seen wild strawberries growing on a rotting log, so this is probably how.

Thanm you for this. I have to give a talk about hugelkultur next week and I know the nitrogen question will come up.
 
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