Re: Gypsum and clays

The thread with Linda and Ellen reminds me of something I observed many years
ago in Idaho.

The soils on the football playing field fifty some years ago (now a housing
development) had a silt loam character with a fairly high clay fraction.  The
clays in that area are derived primarily from basalts, quite unlike our
eastern clays.

The school had a gizmo that lined the field with Gypsum marking the boundaries
and the ten yard marks.  There was a line several inches (four or so) wide,
perhaps an inch high.  During the winter the miniscule rainfall--perhaps four
to five inches total--carried some of that material down into the soil.  The
next spring the grass where the lines had been was two to three times as tall
as the rest of the field, much deeper green in color and arrestingly vivid.

That's when I started asking questions what had been used--and it was
agricultural Gypsum. I've never forgotten that image.

The general area had patches of "slicks" that were extremely rich in sodium,
sticky when wet, cracked deeply when dry.  They were underlain by caliche--an
impenetrable layer of lime formed through leaching of the surface layers.  To
farm over a slick was to invite trouble.  I saw tractors buried up to their
axles (two to three feet!) because the "slick" was water-saturated.  Gypsum
was the material used to correct the condition--or deep plowing down through
the caliche layer to mix it into the soil.  I suspect it contained both lime
and gypsum.

Perhaps our clays--these acid red sticky ones--may not respond to gypsum as
well, but I have used quite a bit here as top-dressing on lawns and in the
iris beds.  I believe the texture of the soil is definitely affected.  The
process takes time.  I've seen recommendations that say use a *pound per
square foot*! of gypsum and till it in.

Neil Mogensen   z 7, mountains of western NC near Asheville

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