Re: Seaweed'n'Salinity

Nan Sterman wrote:
> 
> >What springs to mind is the Mesapotamian region which in very early
> >times, although virtually without rainfall, had highly fertile land
> >beside its rivers due to extensive irrigation.
> 
> Moira, I would expect that the fertility had more to do with nutrients
> deposited into the soil from the fish and other animals that live(d) in the
> river.  River valleys are typically fertile as a result of years and years
> of nutrient deposits.  Is this what you had in mind?
> 
 Nan
I seem not to have expressed myself very clearly. What I was commenting
on was not the fertility along the river valley, which, as you say, was
very much the result of the materials brought down by the river from the
distant mountains.

What I was trying to explain was that the ancients ingenously ran the
river water further out than its natural spread to irrigate truely
desert land along the margin and THIS LAND over the centuries, in the
virtual absence of rain, gradually became loaded up with salts until it
was rendered infertile.

Close to the river this apparently didn't happen,  presumably  because
of the natural flushings due to floods, and this much narrower strip is
I believe still in cultivation today.

Which chimes with my contention that soil will normally only accumulate
high levels of salts if not regularly flushed by fresh water or adequate
rain.

Moira
-- 
Tony & Moira Ryan <theryans@xtra.co.nz>
Wainuiomata, 
New Zealand (astride the "Ring of Fire" in the SW Pacific).
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