Re: no-till gardening
John Schlesinger wrote:
>
> >
>
> Moira -As convincingly you present your case for no-till soil improvement, I have to
> remain a skeptic, at least as it would be applied to heavy clay soil, and especially
> the compacted adobe clay we have in this urban environment. My own personal
> experience with adding woody organic material to adobe clay, has demonstrated that it
> works - in that a friable non-compacting result can be achieved, and rather quickly,
> to whatever depth the matter is added (in sufficient quantity). I should not
> extrapolate this to other clays, as I don't have experience with doing this to them.
> But the black adobe clay we have in California is susceptible do such amendment. (I
> am not a soils scientist - perhaps an expert out there can tell us exactly how the
> adobe clay differs from other clays. It does have a very fine particle size, turns
> to goo when wet, and to brick when dry.)
Hi John
I have no doubt that all clays were not created equal and I have to
admit that my recommendations for no-till on clays are based on other
people's experience. (my own soil is a medium loam liberally laced with
pebbles from a fossil river bed).
However, I have encountered a tale perpetuated by a great number of
gardeners on all sorts of clay soils throughout North America. It goes
like this." I struggled with my soil for years to mix in organic matter
by cultivation and achieved very little. Then in desperation I simply
piled organic layers on the surface and within a short time (the first
year in most cases) the clay beneath began to yield and become friable".
The main advantage of clays for gardening is that most of the breed are
as rich in nutrients as they are poor in texture and if you can improve
the latter it gives your plants access to the former.
> in urban California (and probably in many other parts of the urban developed world),
> because wherever housing has been built, the developers scraped the land and
> intentionally compacted the remaining soil, as part of the development process.
Alas, yes, This happens here too. They also add insult to injury by
selling you back the skimmed topsoil!!
> one has to create a soil structure where none exists. I still remain skeptical that this can be accomplished quickly by worms carrying large amounts of surface organic > material several feet into clay.
Well, I think this would take more than a year or two, but there are
very few plants which routinely put their roots down several feet at
least in their early years. I doubt anyway if most gardeners have either
the resources or the energy to attempt soil formation to this depth by
tilling.
(I'd love to read the articles you referred to
> about testing in Israel. Could you give me a reference? Were the amounts of
> organic material at various levels below the surface accurately measured?
As I promised to "riedy", I hope to have this reference available early
in the new year, but I think I should point out that this was an
experiment on no till in agriculture and dealt with existing farm fields
rather than gardens, so it most likely related to already much-cutivated
soils with the intention of finding whether such cultivations could be
reduced.
I don't see
> this happening with sand areas. Barry wrote of an area which I took to be almost
> pure sand. We have that in Golden Gate Park in San Francisco. The entire park, as
> was much of western San Francisco, was originally sand dunes . The park developers
> brought in soil to place over the sand, and there has been heavily mulched parkland
> over most of the area for over 100 years now. Yet, if you dig down, you still find
> the sand dunes underneath, and they are still basically sand. Yes, there is some
> organic material (and silt) mixed in, but not enough that you would call it soil - it
> is still basically sand.
I wonder if this matters all this much. With most plants the bulk of the
feeding roots and their associated microorganisms live no deeper down
than the top 10". It's only the "water" roots that penetrate deeply.
Certainly, if the deeper sand can be augmented even with some orgainc
matter it will help water-retention and cut down on the need for
artificial watering in dry regions, but this will have little effect on
the plants' nutrition. What usually happens in such cases is that most
annuals and perennials can be accomodated in the improved top layers,
but the trees and shrubs which will flourish are those suited to the
area - capable of very deep rooting. Well-adapted species can usually
put their water roots deep enough to reach the permanent water-table
however deep down it may lie.
-
Moira
Tony & Moira Ryan <theryans@xtra.co.nz>
Wainuiomata, New Zealand. (on the "Ring of Fire" in the SW Pacific).
Lat. 41:16S Long. 174:58E. Climate: Mediterranean/Temperate
