In article ,
"David Hare-Scott" wrote:

Doug Freyburger wrote:
Una wrote:

In places with high salt content in the soil already, soil
amendments that are high in salts can be bad news.

I take it salt in soil is a sign of poor drainage and/or insufficient
rainfall.

Not necessarily, it is a complex issue with more than one cause, see:

http://en.wikipedia.org/wiki/Soil_salination

When Rome finally took out Carthage they plowed salt into
the soil. Carthage never came back from that and the place is still
desert today, but the soil is no longer salty. Even in a desert
there's been enough rain and drainage to leach it all away centuries
ago.


Yes rainfall will tend to remove salt just as it leaches all soluble salts
over time. It isn't clear to me if the proverbial application of salt by
Rome resulted in the desert, I suspect there is more to it than that.

I thought that the forests of north Africa met the same fate as the
forests of Britain (cut to make ships), however I don't seem to find a
supporting cite for that opinion.

One of the long term problems with pumping well water and other
irrigation for crops is it tends to build minerals in the soil faster
than natural drainage.

That can happen but it is not the only way that soil damage can be caused.
Irrigation water can raise the water table so that salty water that was
safely buried comes up to interfere with plant growth

The soil moves towards desert over a period of
centuries. There are vast deserts in the world that were once lush
agricultural lands. The desert of Iraq was one of the birthplaces of
agriculture and there was a History Channel show this week on a Sahara
site that was once a grain farming community.

I wouldn't assume that all that was all due to salinity, over grazing and
other mismanagement contributed. It is much easier to damage soil and allow
deserts to encroach than the reverse.
I think you'll find that the raising of the salt level in the land
between the Tigris and the Euphrates rivers via irrigation is the
accepted mechanism for the collapse of agriculture there.

See:

http://en.wikipedia.org/wiki/Desertification

I seem to recall that there have been some climate change effects in the
fertile crescent too (over millenia not the last century) but I cannot find
the reference to it.

David
--
- Billy
"Fascism should more properly be called corporatism because it is the
merger of state and corporate power." - Benito Mussolini.
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