Re: no-till gardening

I think Richard Starkeson has made a very apt observation about topsoil
being linked to rainfall  ("I think the principal reason we have so
little loamy topsoil here, is because with the light seasonal rainfall,
there isn't enough year round moisture to allow for soil buildup through
decomposition of the plant material on the surface, and that the growing
season is so short, thus not producing (in the grasslands) a lot of
annual vegetative debris.  Even in our heavily forested areas, there are
only a few inches of humus on top of the subsoil.")  Living as I do in a
desert area (desert as defined by the evapotranspiration rate) with
heavily alkaline adobe clay soil and normally an annual precipitation of
8 inches (200mm), on a half-acre with 200 large deciduous trees (so you
can imagine the fall of the leaf in autumn), I can attest that my soil has
no topsoil or humus except where I have created it by the old spade,
incorporate and liniment method. But I have to continually water to keep
these areas friable and keep the earthworm population alive. Where I have
allowed fairly dense copses to develop and remain untouched, there is
little leaf debris build up from year to year.  This is because the
debris is bone dry for the most part and very high spring
winds scour the area before the trees are leafed out enough to keep the
winds from blowing the leaves away.  

I would be very interested in seeing the Israeli report, especially to
see what their moisture management is.


On Wed, 15 Dec 1999, Tony & Moira Ryan wrote:

> Date: Wed, 15 Dec 1999 12:25:11 +1300
> From: Tony & Moira Ryan <theryans@xtra.co.nz>
> To: Mediterannean Plants List <medit-plants@ucdavis.edu>
> Subject: Re: no-till gardening
> 
> Tony & Moira Ryan wrote:
> > 
> > Richad Starkeson wrote:
> >  But the compost on top of the soil method will take a good deal longer
> > > than working it into the soil to some depth, and it won't be amended as deep.
> > 
>  Hi Richard
>  
>  Strangely, and against all received wisdom and common sense both
>  individual observations and formal experiments disagree with you in
>  this.
>  
>  Field-scale trials in Israel a few years ago were done to find our
> which
>  was the best way to incorporate organic matter (compost) in soils. They
>  compared conventional ploughing, rototilling and simply applying the
>  compost to the surface.
>  
>  They found that the surface application was in fact the most effective
>  and the ploughing the least, both in the general amelioration of the
>  soil texture and the depth of the improvement. After three years on the
>  undisturbed plot traces of the added organic matter were turning up in
>  the lower soil a full metre below the surface, well below those in the
>  other treatments.
>  
>  As to more informal observations, at least with clay soils we have had
>  many people on the organic list talking of how they tried
> unsuccessfully
>  for years to improve their gardens by digging in organic matter, and in
>  despair finally built beds on the surface instead - only to discover in
>  a very short time a rapidly-developing depth of good usable soil in the
>  underlying clay.
>  
>  In fact it is possible to offer a logical explanation. As nature has
>  only very limited means of digging soil apart from areas with burrowing
>  animals, she has had to develop a mechanism for incorporating into the
>  soil materials which accumulate on the surface. To accomplish this a
>  very complex organisation involving all sorts of soil inhabitants has
>  evolved and these inhabit the surface layers of the soil. I must stress
>  the word "organisation", as it is evident they do not act randomly but
>  work together like people in a factory. There is definite structure in
>  an undisturbed soil with such easy-to-see features as the burrows of
>  such creatures as worms and ground beetles and many smaller pores we do
>  not usually notice. This open sponginess of the topsoil/mulch layer is
>  held in place by natural glues produced by certain fungi and other
>  organisms and is quite firm and elastic enough to resist destruction by
>  such things as normal treading. Associate with the soil structure are a
>  great variety of microorganisms, chiefly (but by no means exlusively)
>  bacteria and fungi. These each have their own working space and
>  preferred soil level and if undisturbed are amazingly active in dealing
>  with organic matter falling on the surface and turning it into useful
>  humus.
>  
>  It does not take a great deal of effort to picture how drastically this
>  peaceful scene of industry can be disrupted by the spade or (even
> worse)
>  the tiller. Not only are the main structures of the surface soil
>  destroyed, but  many of the inhabitants are likely to be killed, not
>  only being physically chopped (worms mostly) but by being either buried
>  to deep to survive or conversely being exposed on the surface. In fact
>  digging seems to be particularly disruptive on clay soils. While loams
>  will apparently recover their structure after several months, clays
>  seem to be more sensitive and very often revert to a wholly intractable
>  state.
>  
>  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
> 
>
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