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Re: Organic matter's effect on soil bulk?



Michael Maas wrote:
> 
> So let me make this a practical question.
> 
> I have an area about 50'x100' that is leveled out mine tailings from
> hydraulic mining.  The soil is long gone, washed down the river in the
> late 1800s.  What is left is about 15 to 20' of rock.  Someone pushed the
> rock out into a flattened plateau in the past but little grows there.
> 
> I have been thinking of what I might start dumping on this area to build
> up an organic/soil base so that it might eventually sustain plants.  Chips
> from the local tree trimmers are available, as well as straw/hay and the
> red clay that is abundant in the locality.  Good loam or even good topsoil
> is more rare and more expensive.
> 
> Given these materials what might one do to build up a base into which
> plants could be placed and expected to survive and prosper?  What plants
> might themselves be used and what chemical amendments might be added to
> aid the decomposition process?
> 
> Ideas?
> 
> Thanks,
> 
> Mike Maas
> --
> Mike Maas                                               (510) 658-0487
> Masimo Consulting                                       2701 Woolsey
> specializing in Sybase DBA Issues and Data Recovery     Berkeley, CA 94705-2606

Mike . . . You have a major job facing you! The simple math is 
that your 50' X 100' section is 5000 square feet of land and if
you garden to a debth of 1 foot, you are talking 5000 cubic feet 
of soil! A conventional sized dump truck carries about 350 cubic 
feet. The organic content of soil should be right at 30%. Ball park
figures are about 10 truck loads of top soil and 5 truck loads of 
organic plus you may well also have the problem of a totaled 
mycorrhizae population. (see attached)

This is too much of a major project to mess around with almost 
right answers. Rather than using wood chips from the local tree
trimmers, think in terms of composted and screened tree trimmings.
Stay away from the clay, go for a really good grade of top soil. 
Talk it over with the pros. You are talking lots of work and lots of 
bucks. 

The people at Berkeley Hort Nurseries seem to be on top of soil 
problems. My best advise is to talk it over with them and maybe some
of the soil people at U.C. Berkeley. You've got a major problem 
but you are also close to some major experts. . . Bill
                          Mycorrhizae 
                               by
                         Bill Robinson

Mycorrhizae are symbiotic soil fungi, present in most soils, that attach themselves
directly onto the roots of most plants. They help the host plants absorb more water
and nutrients while the host plants provide food for the fungi.  Because the surface
area of the hyphae, the feeding structures of the mycorrhizae, may be several
hundred times the surface area of the roots, the mycorrhizae can feed on a larger
soil mass than the roots and they do so more thoroughly. Mycorrhizae have the
potential to be a central nutritional source for the host plant. Mycorrhiza also seem
to cause the host to increase the production of certain metabolites but those studies
are incomplete.

One study compared the fresh weight of a group of different  roses whose roots
had been inoculated with two different mycorrhizae against the weight of the same
varieties grown without mycorrhizae. The inoculation was done by dusting the rose
roots with spores of the mycorrhizae at the time of planting. The mycorrhizae
employed were Glomus deserticola and G. intraradices. After several months the
roses were dug up, washed to remove any foreign material, and then weighed roots
and all. The inoculated  roses showed significant increases in weight in every instance.
Some of the roses did better with G. deserticola while others did better with G.
intraradices. In one instance a miniature rose showed a 75% increase in fresh weight 
with both of the test mycorrhizae.

If the conditions are right, a viable mycorrrhizae colony can help the plant  become
more vigorous, more salt tolerant, less fertilizer dependent and more tolerant of 
chronic low moisture - but the key word is, "if" and there are qualifiers. First, the
mycorrhizae are relatively fragile. They thrive when the organic content of the soil
is high but  languish when the organic content is low. Mycorrhizae also resent having
the soil disturbed. Rather than digging in organic material and disturbing the soil, it
is best to simply put down  a 2" layer of compost in the winter and another 2" layer 
in the summer. The mycorrhizae sends hyphae to this rich organic layer as a prime
nutritional source.

Mycorrhizae are destroyed when the soil is fumigated, sterilized, solarized or drenched
with most of the  pesticides used to control nematodes, grubs, or weeds. They are also
sensitive to high levels of chemical fertilizer. There is a difference of opinion as to the 
mechanics. Some research workers say that excessive chemical fertilizer burns the
hyphae just as it burns roots and the performance of the mycorrhizae falls off because
they have been injured. Others research workers say that the high levels of chemical
fertilizer, especially phosphorus,  cause the plant roots to shift feeding patterns away 
>from  the mycorrhizae. There are many unresolved issues about the way mycorrhizae 
take up mineral nutrients and particularly phosphorus. There is, however, general
agreement  that avoiding high levels of chemical fertilizer,  particularly phosphorus, 
promotes a more vigorous feeding through the mycorrhizae. The best management of
mycorrhizae is to simply use composts with added composted manures to feed the
plants while, at the same time, feeding the mycorrhizae. 

Note , because mycorrhizae are fungi,  they are sensitive to fungicides. There are a
few scattered reports showing adverse effects on the mycorrhizae as a result of the use
of garden pesticides but the studies seemed incomplete. 

Finally, mycorrhizae are relatively plant specific. A mycorrhiza that gives a good
response with one rose may give only a fair response with another. One way around 
this is to inoculate the rose at the time of planting with a "cocktail" containing a
number of different mycorrhizae. A small amount of the mix is simply applied directly 
onto the root of the plant host.   In time the various mycorrhizae will battle it out to 
establish the dominate colony. Commercial inoculum mixes containing a variety of 
viable spores are starting to become available.   

Mycorrhizae may be of particular value here in Southern California where our tap 
water is alkaline. Iron, one of the essential nutrients, reacts with certain organic 
components in the soil to form complex chemical structures. The roots can not absorb
the iron from these  structures when the conditions are alkaline. In essence, the iron
is "locked up" within the chemical structure and is no longer available to the root. The
mycorrhizae, however, seem to be able absorb this "locked up" iron. Studies on the way
mycorrhizae are able to do this are on-going.

BioOrganics Supply Center in Camarillo sells a  "cocktail"  containing spores of Glomus
intraradices, G. deserticola, G. etunicatum, G. clarum, and G. mosseae. This seems a
good mix for my garden which contains a collection of various Old Garden Roses,
English Roses, a few modern roses,  a variety of perennials, shrubs, and ground covers.
I am adding some additional Old Garden Roses and English Roses.  My plan is to dust
the roots of  these new roses with this "cocktail"  and to allow the various mycorrhizae
to spread through the garden on their own. I have high hopes for a way around my
problems with my alkaline tap water and the iron nutrients. We'll just have to wait and see.



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