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9064Re: Wood chips as mulch: Re forest soils and more soil science

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  • Jeff
    Feb 28, 2009
      This email is an attempt to clear up the misunderstanding that have
      arrisen as of late about wood mulch
      -and of course how this relates to forest soils and
      how separately it relates to natural farming

      I will start with the sciency part,., then get more common speak as
      the post goes on

      > It would seem to me that the fact that many forests have super
      fertile top soils that are many feet deep could possibly be that
      multitudes of > leaves, sticks, branches, trunks, etc., have fallen
      undisturbed over > millenia.

      when you say fertile soil you must have a basis of comparison..
      ok so old prairie soils have deep dark A horizons.. the rotting roots
      of the grasses are responsible for this .. this is the theory behind
      'rhizodeposition' that Bob Monie toughts..
      this works because of several factors..
      a) grass roots go deep instead of spread out like forests
      b) grass roots are upto 75% of the primary production as opposed to
      around 18% for trees (mostly goes into 'wood')
      c) roots actually are somewhat resistant to decomposition due to
      content of anti-microbles and higher percentages of lignin
      so the result is somewhat decayed organic matter with high nutrient
      value mixed deeply in the soils lll this is for prairie soils

      in forest soils the majority of the organic matter is above the soil...
      the leaf and stick litter is called the o-horizon...
      in frigid climates like boreal forests this can over eons become
      several feet thick, also in bog/peat situations this can likewise
      become thick- this is due to slow decomposition because of cold or water..

      in temperate climates it is at most inches thick...
      in tropical climates it is even less (usually less than 1")

      immediately below the O-horizon is an E horizon... this is where all
      the acids from the leaf litter remove the nutrients and send them
      packing.. ending up in the stream or deeper in the soil profile...

      the nutrients then are bound mostly in the living matter and the
      O-horizons..... (recently dead stuff)

      but the soils are often 'deep' because the acids do break down bedrock
      and roots crack it to increase weathering of the soil...
      so the actual soil profile might be deep but the nutrients are still
      mostly shallow...

      I fail to see how adding wood chips to soils could possibly
      > decrease the fertility of soils, unless one has been adding chemical
      > fertilizers for quite some time, resulting in dead soils. Perhaps
      I'm mistaken?
      It doesn't decrease the fertility... it temporarily sequesters
      them.... this has to do with the natural balance of the carbon to
      nitrogen ratio.... this topic has been covered several times in the
      basically bacteria have a low carbon to nitrogen ration relative to
      the wood chips this means the bacteria suck up all the nitrogen so
      they can break down the wood chips... the bacteria being tiny and
      numerous are much better at getting the nitrogen then the plants are.
      so for 1-3 years you have low 'available' nitrogen until the bateria
      catch up with the wood chips...

      the nitrogen fertility of forest soils is usually built up during the
      early successional phase of the forest.. that is in the meadow and
      shrub stage.. there are many meadow and shrubs that fix nitrogen and
      very few trees that do so.. typically the nitrogen is maxed as a young
      forest and slowly declines as some is washed out...
      it is the bacteria and fungi's ability to hold onto the nitrogen so
      well that enables the forest to be so productive without fertilize..
      when you cut down a forest you do away with their food supply and the
      bateria and fungi die, and the nutrients get leached.

      > > Dear Jeremy,
      > >
      > > I think woody material contains high amount of cellulose. It
      > decomposes very> > slowly and after decomposition that releases
      toxic acids that can be problematic to the plants.. I dont know the
      specific names of these acids.

      this is only true of certain trees .. not all trees have these
      compounds..... trees that are noted for their resinous oils (Eucalpyt,
      leaurals) and conifers (pines, spruces etc) are likely to result in
      these acids..
      there are many many specific ones, and plant biologist and soil
      scientist have different terms for them.. the
      term I'm familiar with is phenolitic...
      pheno- refering to the benzene right structure of these acids...
      and litic refering to lysis.. or the breakdown of the orginal organic
      There may be other compounds that contribute to this but they are less
      known.. and don't occur in large families like the previously
      mentioned plants

      this is one of the reasons conifers are not highly recommended as
      mulch for gardening.....and braodleaved trees are prefered...
      I would think a moderate amount of conifers once or twice would have a
      minimal effect...
      generally when these things are measure and disscuessed it is in the
      terms of geologic time development of soils...

      I would think that after once or twice adding the conifers, and
      regular mulching of other organic matter, you would no longer need the
      conifer mulch to effectively garden and restore fertility

      > > > If I recall correctly, woody material has such a high carbon
      > content that it ties up nitrogen unless broken down by fungi. As
      already mentioned, you can bury the material to help it decompose. You
      could also spread the chips out and innoculate with fungi spores. You
      may want to try Stropharia rugoso-annulata or Pleurotus species.
      > > >

      this is exactly correct...
      interestingly enough research pointed to by Stamets in Mycellium
      Running indicated increased yeild for certain vegetables when grown in
      combination with the above mentioned fungi...
      and even more interesting was that fact that the best yeild increases
      were for the brasicas ... which don't form VAM or AM mycorhizal
      assocaions like most other plants.

      just say so you have any questions or need anything clarified..
      I'm fighting a cold and might have skipped over something important
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