On Sun, 06 Mar 2005 15:40:53 GMT, "Alex Woodward"
wrote:

I would like opinions on whether an application of sulphur will turn soil to
acidic or not. Does it work and are their any side effects?

I've never used sulphur, but.....

A soil is alkaline nearly always because of the its mineral content,
usually chalk (aka lime). Some soils only contain a small amount of
chalk and are mildly alkaline (say pH 7 - 7.5), while other types
contain large amounts of chalk and are, relatively speaking, strongly
alkaline (say pH 7.5 and above).

As long as there is free chalk in the soil, it will be alkaline.

In order to make the soil acid, you have to dissolve or otherwise
remove the chalk. This is not a simple undertaking.

A mildly alkaline soil can be made a little less so by adding lots of
organic matter as peat or compost. As the organic matter rots down, it
liberates acids that will temporarily lower the acidity of the soil.
But unless you regularly add more compost etc. the soil will
eventually revert to its mildly alkaline state. Over many years,
repeated application of compost may bring about a more-or-less
permanent change in the alkalinity.

Sulphur works in a way similar to compost, in that it slowly oxidises
in the air and releases sulphur acids (sulphurous and sulphuric,
mostly the former) into the soil. But eventually the sulphur will be
used up and a repeat application will be necessary, but how long this
takes, I don't know. How long is a piece of string?

The biggest problem with alkaline soils is that certain trace elements
are immobilised by the alkaline conditions, so cannot be taken up by
plants in sufficient quantity for their needs. Iron is the obvious
trace element here, but availability of manganese can also be a
problem. Ericaceous plants (rhododendrons, azaleas, camellias, some
heathers) have a high demand for iron and cannot flourish on alkaline
soils without help, whereas other plants with a more modest
requirement can grow very well. But iron and manganese can be supplied
artificially in a complexed form that ericaceous plants can absorb,
when it remains mobile in the soil and can be taken up by the roots.
There are several fertilisers available in garden centres that contain
these complexed trace elements. Look for ones particularly formulated
for ericaceous plants, or containing sequestered or complexed iron and
manganese. But one application has only a limited life, and you have
to re-apply at regular intervals.

Some of these fertilisers claim to acidify the soil: it is highly
unlikely that they do (but I've never actually done any tests). But
they will allow you to grow acid loving plants on an alkaline soil,
and their claims about changing the acidity are just the product of an
over-zealous marketing department!

For a mildly alkaline soil, I'd go for the complexed trace element
route with lots of extra compost, rather than adding sulphur. If
you're on a heavy chalk soil, you're really trying to push water
uphill.



--
Chris

E-mail: christopher[dot]hogg[at]virgin[dot]net