9068RE: [fukuoka_farming] Re: Wood chips as mulch: Re forest soils and more soil science
- Mar 1, 2009I could argue with this but I am not as scientifically based as Jeff so I
would certainly say things wrong BUT my understanding is that the wood chips
lock up nitrogen ONLY if they are dug into the soil. Left on top they do not
'pull' nitrogen out of the soil. I believe there are studies supporting and
dissenting this view but a couple of supporting sites are below:
A 2004-2006 Washington study showed that applying a 5-foot wide, 6-inch
thick layer of wood chips provided the best weed control in all three years,
although it needed reapplication in year three. This treatment also produced
the greatest tree growth and fruit size.
In a related trial, a Gala apple block was used to compare a 4-inch wood
chip mulch in the tree row with a herbicide strip. In the first year,
mulched plots consistently had 15 percent to 20 percent higher soil moisture
at the end of each irrigation cycle than the bare ground plots. In the
second year, the two treatments were watered independently according to
need, and mulching reduced cumulative irrigation application by 20 percent
to 30 percent.
Concern: Wood chip mulches will tie up nitrogen and cause deficiencies in
Evidence: Actually, many studies have demonstrated that woody mulch
materials increase nutrient levels in soils and/or associated plant foliage.
My hypothesis is that a zone of nitrogen deficiency exists at the mulch/soil
interface, inhibiting weed seed germination while having no influence upon
established plant roots below the soil surface. For this reason, it is
inadvisable to use high C:N mulches in annual beds or vegetable gardens
where the plants of interest do not have deep, extensive root systems.
From: http://www.sustainable-gardening.com/WoodChips.php and an interesting
[mailto:firstname.lastname@example.org] On Behalf Of Jeff
Sent: Sunday, 1 March 2009 1:17 PM
Subject: [fukuoka_farming] Re: Wood chips as mulch: Re forest soils and more
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 superfertile 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
I fail to see how adding wood chips to soils could possibly
> decrease the fertility of soils, unless one has been adding chemicalI'm mistaken?
> fertilizers for quite some time, resulting in dead soils. Perhaps
>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,toxic acids that can be problematic to the plants.. I dont know the
> > I think woody material contains high amount of cellulose. It
> decomposes very> > slowly and after decomposition that releases
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
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
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
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 carbonalready mentioned, you can bury the material to help it decompose. You
> content that it ties up nitrogen unless broken down by fungi. As
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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