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EDG
2010-Apr-19, 02:31 AM
While reading some volcano articles on UT, I was reminded of something I'd kinda taken for granted - why is volcanic soil so fertile? I'd always heard that it was, but never really understood why.

AFAIK the ash and tephra doesn't contain organic material, does it? Or is the fertility due to all the dead plant matter that's under the fallen ask?

DrRocket
2010-Apr-19, 03:11 AM
While reading some volcano articles on UT, I was reminded of something I'd kinda taken for granted - why is volcanic soil so fertile? I'd always heard that it was, but never really understood why.

AFAIK the ash and tephra doesn't contain organic material, does it? Or is the fertility due to all the dead plant matter that's under the fallen ask?

Who said that they are ?

Around here we have some volcanic soil in some of the most god awful desert you could ever hope to see. It does not appear to be at all fertile.

http://sssf.byethost31.com/geology/303288.htm

01101001
2010-Apr-19, 03:23 AM
University of California, Santa Barbara, Volcanology: Soils from Volcanoes (http://volcanology.geol.ucsb.edu/soil.htm)


Why do people live on dangerous volcanoes? The main reason is the rich volcanic soil. People are willing to take high-risk gambles for the most basic things of life -- especially food.
[...]
Volcanic rocks make some of the best soils on earth because they not only have a wide variety of common elements the rock and are readily chemically separated into elemental components.

distraction tactics
2010-Apr-19, 03:31 AM
It's important to keep in mind how soil forms as well - within the weathered zone of rock - and the time involved in its formation. Basaltic rock weathers very nicely, given its mafic component and tendency to be porous.

DrRocket
2010-Apr-19, 03:58 AM
University of California, Santa Barbara, Volcanology: Soils from Volcanoes (http://volcanology.geol.ucsb.edu/soil.htm)

From that same link

" But that is the short-term effect. In the long run, volcanic deposits can develop into some of the richest agricultural lands on earth."

Bold added.

No one disputes that some very fertile soils are volcanic in origin. But that does not mean that all volcanic soils are fertile.

Soild in flood plains of major rivers can also be very fertile. The land can also be a swampy morass.

Agricultural people pick the best land and avoid that which is unsuitable, whether it be volcanic or otherwise.

Gillianren
2010-Apr-19, 04:05 AM
Mmm. "Would prefer to avoid" that which is unsuitable. There's a lot of poor land which gets farmed anyway because the people farming it don't have a lot of choice in the matter.

EDG
2010-Apr-19, 04:34 AM
Fact is, volcanic soil often is very fertile, which is why people keep building villages and farms around them. I'm not really interested in nitpicking about semantics here, I'd just like to know what it is about volcanic soil that makes it (sometimes?) so fertile. That links helps, but doesn't actually tell me what it is in the soil that the plants like so much.

Jens
2010-Apr-19, 05:46 AM
The first paragraph of this paper (http://www.ctahr.hawaii.edu/mauisoil/b_andisol.aspx) seems to be a pretty good basic explanation. I think you could delve further from there. But it says that due to its properties, it holds organic material well. And retains water, and is easy to till.

Ivan Viehoff
2010-Apr-19, 08:12 AM
Volcanic soil is often one of the best mineral mixes to make soil, because of its mechanical properties and minerals available, including in particular trace elements that other soils ca be short of. Transmission of trace elements in volcanic aerosols is important in maintaining the fertility of some other soils - the absence of such trace elements can be a reason why some such soils lose their fertility. But, except in very poorly developed economies, man is usually capable of diagnosing trace element shortage and spreading them on via mineral supplement.

But volcanic soils can also be of poor fertility, as sometimes they contain unpleasant things. Icelandic volcanoes are notorious for the fluoride content the ash can contain, which is sufficient to cause substantial damage to agriculture when it arrives in sufficient quantity. Worse, some plants normally browsed by animals are capable of taking up the fluoride, which makes them poisonous to those animals. These effects were prominent in the Laki eruption in the 18th century, when much of the livestock in the country died from eating plants which had taken up the fluoride. The loss of some soils is also dated to this time - vegetation died off and soils were blown away.

It is also notable that one reason that some lava-fields in Iceland are almost devoid of vegetation because of the mechanical properties of the substrate. Some can be very porous so retain little water, and any seedlings that might otherwise be established are sandblasted by wind-borne particles. The Icelanders have learned that you can stablise such soils, which leads to them being colonised. Other such lavafields can be very hard, allowing little opportunity for roots to penetrate. But these hard lavafields will be colonised in time if there is sufficient rainfall. In south Iceland is one such hard lavafield from the Laki eruption that is today completely covered in a thick layer of moss. This is facilitated by the fact that it is one of the very wettest areas of the country, but apparently it was severely set back when they had a dry month in a summer a couple of years ago. It is reckoned that with the passage of time this moss will form the basis of a soil which will eventually allow the lavafield to be colonised by higher plants.

There have been reports on Iceland Review (by leading Icelandic photographer Pall Stefansson) of flocks of birds being killed by flying into the ash cloud in Iceland.

Warren Platts
2010-Apr-19, 11:03 AM
Lunar soils should turn out to be fertile as well then.

Strange
2010-Apr-19, 11:12 AM
I read that you can date lava fields fairly accurately by the type of vegetation that has taken hold. Lichens are first - but that is all I remember!

galacsi
2010-Apr-19, 07:05 PM
Soils form from the weathering of substratum . And soils derived from lava and particularly basaltic lava are very rich in minerals. Basalt is very rich in calcium , potassium and phosphorus and give very fertile soils. When young , because with time and too much rains , these soils become depleted of of their minerals and can evolve into laterites or podzol depending of the climate.

01101001
2010-Apr-20, 12:37 AM
Lunar soils should turn out to be fertile as well then.

Herald Journal: Lunar Soil Is Proving Fertile, Sept. 27, 1969 (http://news.google.com/newspapers?nid=1876&dat=19690927&id=Y4EsAAAAIBAJ&sjid=K80EAAAAIBAJ&pg=1602,5114433)


Space officials report [...] The lunar soil gives evidence of good fertility.

Mare Fecunditatis!

neilzero
2010-Apr-21, 01:59 PM
Plants need water, sunlight, carbon dioxide, nitrogen compounds, potassium compounds, phosphorous compounds. If any of these are less than one part per million, plants do poorly. Perhaps a dozen other elements are also essential at parts per billion. A small amount of volcanic material assures that most of these needs are met. Non volcanic soil often is lacking in some essential, and thus requires fertilizer. Some volcanic soil has too much of one or more element, so not all volcanic soil is fertile. Neil

JonClarke
2010-Apr-22, 08:14 AM
Volcanic soils are often rich in easily weathred materials, espeically glasses, and developed on ash which has a high surface area, which means they weather quickly. Bewcause of their granular nature they tend to be well drained but also have good waer storage quality because of they clays.

trinitree88
2010-Apr-22, 08:32 PM
In countries where food is in short supply, the additional benefit of planting in weed-seed free soil cannot be discounted either. A huge energy budget is expended in weed control, and if your recent eruption buries the weeds beyond their germination depth, more power to it, and a farmer can enjoy a couple of years of pristine farming conditions. The American indians would girdle the trees in the Eastern forests, let them dry for a year, then torch them up. The resulting forest fire would kill most of the weeds and their seeds, giving ample yields of beans , corn, cucumbers, squash and pumpkins when planted. If allowed to meadow, deer favored the burnouts for their lush grasses.