Re: CULT: gypsum as soil conditioner (was Borax)

 Remember all those boring posts from me about types of clay, soil
texture, soil structure, soil organic matter, and soil aggregates?
Here's some info about gypsum I found on the web in relation to clays &
changing their characteristics.  .... a recipe for coping with those
awful shrink/swell "sticky" clays as opposed to the good clays that are
easy to fix up with organic matter and sand:
----------------------------------------quoted
from--------------------------------------
<http://www.pottingmix.co.nz/gypsum.htm>

Gypsum as a 'Soil Conditioner'

     Many heavy clay soils are classified as colloidal; in other words,
the clay particles are of such microscopic
     dimensions that they remain in constant motion and are not
stabilised into crumbs; that is, they have no structure
     as previously defined. The worst type of sticky clays often have a
relatively high sodium content and are loosely
     termed sodium clays.

     When wet, they swell up with water and are impossible to work and
when dry they split open with deep cracks
     forming blocks that are as hard as bricks.

     When gypsum is applied to such clays the colloidal particles are
caused to flocculate, that is to say, the colloidal
     particles will fly together to form flakes aggregates or 'crumbs'.
This occurs when the free calcium released by the
     gypsum displaces the sodium from the clay complex and forms a
calcium clay which has much greater stability.

     Working compost or sand into heavy clay is very difficult and
largely ineffective in improving the soil structure
     homogeneously unless the clay is first stabilised into crumbs by
the heavy application of gypsum, after which the
     job of incorporating sand and compost is greatly facilitated.

     Working gypsum into stubborn clays is best done progressively by
applying the gypsum first to the surface at the
     rate of 1 kilogram per square metre and making no attempt to work
it in beyond the top six centimetres, a job best
     done with a claw hoe. After a few days it will be found that the
surface has become more crumbly and workable at
     which time another dressings is given and the soil worked lightly
with a fork, this time to a depth of about 15
     centimetres.

     During the process the crumbly gypsum-Ioaded surface material falls
amongst the cracks of the deeper soil and
     separates the lumps without necessarily bringing them to the
surface.

     Thereafter the soil is allowed to rest for a week or two and with
intervening rains the gypsum is mobilised and goes
     to work on the deeper lumps. Finally, sand and compost can be
incorporated thoroughly when the full top 15
     centimetres of clay is found to be workable and relatively friable.


     For the incorporation of compost, the moisture content must be just
right, neither wet nor dry, but just slightly damp.
     Depending upon how the rain falls, one might have to wait for
several weeks for precisely the right moisture content
     for working.

     Alternatively the area can be covered with plastic sheeting and
tested for moisture content regularly until it is just
     right. This technique can overcome the frustration of rain on the
clay just when it was least desired!

     *Australia and New Zealand Gardening -Composed by Peter Bennet
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Linda Mann east Tennessee USA zone 7/8
East Tennessee Iris Society <http://www.korrnet.org/etis>
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