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Composts do increase soil pH. Organic matter
and
manure can , on the other hand decrease pH by
increasing
its acidity. Compost is stable organic matter and has
lots
of organic compounds that do have a buffer effect in
soil
pH ( they resist to sudden changes in soil
pH).
Compost contributes with some Calcium, Magnesium,
Potassium
and also Sodium. All those cations can influence soil
pH with
Sodium and Potassium being the ones that would influnce
pH
the most.
I believe that the effect on soil pH is also an
indirect one by the increased
microbial activity leading to the release of blocked
minerals specially
calcium from tricalcium phosphates.
Jose
----
Gil,
The vineyard in question is on acid basalt
derived soils with pH around 5.5 under normal treatment and has skipped
to 6.1 under compost.Interesting to note that most soil cations have also gone
up and their substition for hydrogen may be the reason for the pH in
crease. The vineyard was established with 3 tonne per hectare lime
application and experienced very little soil pH increase. The
compost cost AUS $15 per cubic metre and is much cheaper than
lime.
I am trolling through petiole analysis from
samples taken at the same time to see if any of the increased soil nutrients
are also showing highs in the vine.
I have followed the cation balancing discussion,
Albrecht etc, with tremendous interest and wonder if any one else has come up
with why compost should effect soil pH? At Uni I was told that the
addition of organic material would lead to an increase in acids used by fungi
to digest material and decrease soil pH leading to peat bog idea of high
OM soils being acidic by nature. But what is high? The soils under
compost have only 2 - 3 % OM, what outcome would you get as OM
approaches 5 -10%?
Cheers JL
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