[permaculture] arid soil building

Lawrence F. London, Jr. venaurafarm at bellsouth.net
Fri Dec 4 18:33:07 EST 2009

Dieter Brand wrote:
 > Bob,
 > A dirt mulch is a well known technique used in dry land farming. 
Heavy clay soil with low organic content has the tendency to dry out 
rapidly through capillaries forming in the clay.  The capillaries first 
transport humidity from the subsoil to the topsoil where it evaporates 
when it reaches the surface.  This continues until the clay *closes 
down* and doesn’t give off any more humidity to plants or to the air. 
It still holds some humidity, but to the eye and for all practical 
purposes it is stone dry right down to the solid rock.

To prevent this evaporation, farmers first plough the field to produce a 
fine powdery top layer of soil (the dirt mulch) which means the 
capillaries from the subsoil don’t reach the soil surface and humidity 
is preserved in the subsoil for plants to use.

If this is done after rain and when the soil moisture content in the 
volume of soil that will be tilled (not lower) is low enough for tillage 
without compaction occuring after drying then you will have a dirt mulch
cover with an extra amount of water retained in the lower layers of soil.

After irrigation or rain, the top layer needs to be hoed to prevent 
capillaries from forming in the soil crust.  The hoeing is only shallow 
to a depth of about 3

It is my experience that, if you're not proceeding with planting, then 
you might be better off leaving the crust intact as more water will be 
retained in the lower depths of soil, under the dirt mulch. After all
under the crust you have more loose dirt mulch (unless all the mulch has 
turned to crust - a good reason to create a deeper layer of it
so that a loose layer is retained regardless of rainfall), therefore no 
capillaries formed in the crust, if any, can connect with the dry, hard 
soil underneath, thus no water loss through evaporation through the 
surface crust can occur. It depends on your soil type whether 
capillaries will form in crust. With mine, I would be way better off 
leaving crust formed after rain after tillage to retain more water in 
the soil reservoir for plantings carried out later on. Of course the 
crust needs to be broken then.

If you're doing any brush clearing branches, leaves twigs can be placed 
of garden soil for shade and water retention.

 >  to 6 inches.
 > Dieter Brand
 > Portugal
 > --- On Fri, 12/4/09, Robert Waldrop <bwaldrop at cox.net> wrote:
 > What do you mean by "dirt mulch"

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