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Old 02-10-2016, 08:46 AM posted to uk.rec.gardening
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Default Volcanic soil

The recent Joanna Lumley programme about Japan visited a volcanic island
in the extreme south where the world's largest radishes are grown. I
can't figure out why a pumice rich soil would be any different to
vermiculite or perlite, all 3 having the same properties of air and
moisture entrainment. No mention of nutrients, but there must be some in
volcanic soil? Puzzled...again.

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Old 02-10-2016, 10:27 AM posted to uk.rec.gardening
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Default Volcanic soil


"Stuart Noble" wrote in message
...
The recent Joanna Lumley programme about Japan visited a volcanic island in the extreme
south where the world's largest radishes are grown. I can't figure out why a pumice rich
soil would be any different to vermiculite or perlite, all 3 having the same properties
of air and moisture entrainment. No mention of nutrients, but there must be some in
volcanic soil? Puzzled...again.


Volcanic soil is particularly rich in potassium and is of great benefit to potatoes
so would guess that radishes would also benefit.

Phil


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Old 02-10-2016, 11:55 AM posted to uk.rec.gardening
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On 02/10/2016 08:35, Chris Hogg wrote:
On Sun, 2 Oct 2016 07:46:13 +0100, Stuart Noble
wrote:

The recent Joanna Lumley programme about Japan visited a volcanic island
in the extreme south where the world's largest radishes are grown. I
can't figure out why a pumice rich soil would be any different to
vermiculite or perlite, all 3 having the same properties of air and
moisture entrainment. No mention of nutrients, but there must be some in
volcanic soil? Puzzled...again.

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Not sure this is telling you anything you don't already know, but
volcanic soils world-wide are exceptionally fertile. The slopes of
volcanoes are extensively cultivated for growing crops. The ash in the
soils keeps the structure open and free draining, but at the same time
retains moisture (that sounds a bit Irish! I'm not entirely sure how
it works). The minerals and chemical elements released when volcanic
ash weathers further contribute to the range of trace elements
available for plant nutrition.


I think these things *entrain* moisture, but they don't absorb it. Yes,
it's Irish but the amount they can "hold" is phenomenal, and yet they
dry to a reusable powder. The idea that you can use them to fill
containers on balconies is flawed because, although they seem ideal when
dry, they are extremely heavy when wet!

IME vermiculite is surprisingly quite alkaline due to the presence of
calcium (I think it's on the cation exchange sites, to be boringly
technical). I also find it tends to break down and eventually go
rather claggy. I use perlite in preference, which should have similar
properties to volcanic ash as it's made from weathered volcanic glass,
obsidian*.

A couple of years ago, I saw packets of some sort of 'rock dust' for
sale in my local garden centre, with much printed on the packets as to
how wonderful it was for growing plants (BTWSTWT!). Can't remember the
trade-name, or whether it was specifically ground volcanic ash or
lava, but most quarries with stone-crushing facilities have piles of
discarded dust, as it's too fine to be used for roadstone or
construction work. Perhaps one of the big quarrying and roadstone
groups was branching out. I'm sure if there's a quarry near you,
they'd be happy to let you have a few bags' full for nothing if asked.

Or you could take a trip to Mexico ATM http://tinyurl.com/gv2lor2


*https://en.wikipedia.org/wiki/Perlite

I buy the 100L size vermiculite from builders merchants and, as I have a
small garden, I can use it everywhere. Mixed 1-4 with compost it stops
the soil compacting and makes it dead easy to weed (things just pull out
by hand).
What I can't figure out is what it, or volcanic ash for that matter,
might contain in the way of nutrients to produce the world's largest
radishes! I suppose no amount of feed is any use without a good soil
structure

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Old 02-10-2016, 07:44 PM posted to uk.rec.gardening
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Default Volcanic soil

tephra which has since weathered to rich soils

I gather tephra is just Greek for ash. So how does ash weather into
rich soil? I must be missing something, like where the nutrients come
from. Nothing much will grow in ash surely.


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Old 02-10-2016, 08:49 PM posted to uk.rec.gardening
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Default Volcanic soil

On 02/10/2016 18:44, Stuart Noble wrote:
tephra which has since weathered to rich soils


I gather tephra is just Greek for ash. So how does ash weather into rich
soil? I must be missing something, like where the nutrients come from.
Nothing much will grow in ash surely.


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But you can grow in charcoal


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Old 02-10-2016, 10:20 PM posted to uk.rec.gardening
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Default Volcanic soil

On 02/10/2016 13:16, Chris Hogg wrote:
But the region
around Naples, which includes Mount Vesuvius, is very rich mainly
because of two large eruptions 35,000 and 12000 years ago that left
the region blanketed with very thick deposits of tephra which has
since weathered to rich soils.


A little more recent than that.

The eruption that buried Pompeii dropped several metres of ash, then
added a pyroclastic flow. From memory it's over 10 metres at
Herculaneum. IIRC the last eruption was 1940-something - late WW2.

Andy
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Old 03-10-2016, 08:54 AM posted to uk.rec.gardening
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Default Volcanic soil

On 02/10/2016 20:04, Chris Hogg wrote:
On Sun, 2 Oct 2016 18:44:06 +0100, Stuart Noble
wrote:

tephra which has since weathered to rich soils


I gather tephra is just Greek for ash. So how does ash weather into
rich soil? I must be missing something, like where the nutrients come
from. Nothing much will grow in ash surely.


It's a slow process, and AIUI two things happen in parallel. Simple
organisms like algae first colonise the ash, followed by increasingly
more complex plant forms. At the same time, weathering breaks down the
ash, releasing nutrients such as phosphate and potash, together with
trace elements, and changing the mineral composition of the ash, often
to the clay mineral montmorillonite, found in many weathered volcanic
ash deposits. Montmorillonite has the ability to absorb cations (pron.
cat-ions) such as calcium, sodium, potassium, magnesium etc. and
release them slowly over time or as conditions change. The combined
effect of these two processes is very slowly to make a humus-rich and
very fertile soil. The weathering can take centuries. The island of
Surtsea, off Iceland, which appeared between 1963 and 1967, showed
signs of plant life in 1965, and is now mostly covered in mosses and
lichens, although higher plant forms are now beginning to appear. As
they die and rot down, their compost will contribute to the soil and
assist other plants to grow.

At least, that's what I understand.

See also http://tinyurl.com/hqyq36c, http://tinyurl.com/hhf2z5h and
http://tinyurl.com/jeq7uk7

Many thanks, Chris. That explains everything! Fascinating stuff,
particularly Surtsea, which we're able to observe in real time. 2-5 new
species a year. Impressive!

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Old 03-10-2016, 11:55 AM posted to uk.rec.gardening
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Default Volcanic soil

On Sun, 2 Oct 2016 21:56:24 Chris Hogg wrote:

On Sun, 2 Oct 2016 21:20:18 +0100, Vir Campestris
wrote:

On 02/10/2016 13:16, Chris Hogg wrote:
But the region
around Naples, which includes Mount Vesuvius, is very rich mainly
because of two large eruptions 35,000 and 12000 years ago that left
the region blanketed with very thick deposits of tephra which has
since weathered to rich soils.


A little more recent than that.

The eruption that buried Pompeii dropped several metres of ash, then
added a pyroclastic flow. From memory it's over 10 metres at
Herculaneum. IIRC the last eruption was 1940-something - late WW2.

Andy


Well, yes, but it doesn't say they were the only eruptions, just that
those were the ones responsible for the soils of the area. Vesuvius
eruptions listed here http://tinyurl.com/j85lp76


Er, that takes us to a Google list for Jenolite! At least it does on my
computer!

David

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