Re: CULT: Time release lime? & dolomite

Long, technical, and maybe too much...

Soil pH is complicated.  Bill Burleson (or maybe it was me??) posted
some information and a link to great website explanation last time we
talked about it.

Raising the pH at once is fine, but, depending on the amount applied,
amount of rainfall, acidity of rain, natural buffering capacity of the
soil (resistance to pH change and ability to maintain a particular pH),
the effect may not last long.

Buffering capacity is related to clay content, type of clay, and type
and amount of organic matter.  Generally, more clay (layered clays) &
more decomposed organic matter in aggregates, more buffering.

It would be easy to change pH in acid sand in a high rainfall area, but
it would change right back to the original in no time.  Barry B says he
has acid sand, so probably needs to add more lime more often than those
of us with heavier soil (more clay).

Limestone is calcium carbonate, more or less.  Dolomitic limestone (also
sometimes called dolomite) just has some of the calcium replaced with
magnesium (magnesium carbonate).  Both raise pH the same amount.  pH is
a measure of hydrogen ions (positive charge). Raising pH is accomplished
by replacing positive charge hydrogen ions with some other form of
positive charge ions, usually calcium.  Magnesium works the same way.

As for <time release>, the idea is that limestone is only slightly
soluble in water.  Acidity reacts with the carbonate.  The bigger chunks
the limestone is in, the less surface area there is to dissolve/react,
so the slower the effect.

Slaked lime (the kind that burns moist bare skin) is soluble in water,
so all of it will be instantly available to raise pH.

So, to get an instant effect, use slake lime, or powdered limestone.
Then use coarser limestone to keep it up.  A bag of crushed limestone
from my local supplier is mostly powdered, so it probably gives an
instant effect.  Some is a bit coarser so probably continues to act for
awhile.  The <manufactured sand> from the local limestone quarry is much
coarser, so should last a lot longer, but would take a lot more to get
the same short term effect as the crushed (powdered) limestone.

Calcium (and magnesium) leach out of soil and are taken up by plants, so
amounts will decrease over time.  I remember seeing some research
results years ago when I was trying to guess more about calcium and deep
soil long term storage of organic matter.  In that study, calcium from a
one application of agricultural lime (crushed limestone) had migrated
more than 10 ft into the soil profile after several decades (I think -
not sure of the details, but it was very deep (certainly deeper than
iris roots) and took a long time).

<Not sure I understand the comment someone made about wanting to have a
'time'
                   release effect from the lime. If you want to raise
the pH of your soil, surely you want to
                   do it all at once and not gradually? And wouldn't it
stay that way for some time - hence
                   the need to apply the lime once per year.
                   Cheers, Jan>

--
Linda Mann east Tennessee USA zone 7/8
East Tennessee Iris Society <http://www.korrnet.org/etis>
American Iris Society web site <http://www.irises.org>
talk archives: <http://www.hort.net/lists/iris-talk/>
photos archives: <http://www.hort.net/lists/iris-photos/>
online R&I <http://www.irisregister.com>

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