>
>> In central and south america, civilizations have come and gone,
>>due to soil depletion.
>
>
My only only vision is to develop an organic
>agriculture witch will return (recycle) minerals to the soil.

Organic agriculture is depleting soils because it rely on outside sources of
fertiliser so in the global sheme it is robed from somewhere. else  From the
point
, when the soil is  tilled ,the naturel fertilisation process is
disturbed to such an extent than after so many years ( hundreds to thousand)
the need for chemicals is getting  necessary.( to come back to the initial
potential fertility of the land)
The chemical fertilisation is a very short lived boost of seeming fertility
( because measured in volume of the products and not in nutrients  content
of the food produced). After few years ( 30 , 50 years) the microlife
getting so sparse and minerals so unavailable that it doesn't work anymore
or require more and more unbalanced fertiliser.
The naturel fertilisation process (that happens in undisturbed soil is
producing more and more top soil every year ( it just make sense because the
sun energy is reaching the earth and life started on desert).
>The soils don't really get depleted of its minerals easely but can easely
having its minerals locked  and unavailable to plants because of lack of
biodiversity ( that include the microlife and plants of differentes stories
and nutrients requirements, shallow or deep rooted etc...). there is a
natural minerals cycles too but takes thousands of years ( glacations,
volcanic activities and fires) to complete.
If you are interested in a real sustainable no cultivation ,fertilisation
mean to produce mineral rich food  in a semi paleo way ( you still have to
sow and selecting plants). read Masanobu Fukuoka authour of "The
naturel way of farming","one straw revolution", and road back to Nature.
jean-claude

>Michael, it may be, that is was due to soil depletion.
>Up to now it seemed to me as if the nativ america civilisations
>were destructed by superior military technology and european
>deseases - at least Inca and Aztecs and several north american.
>(According to Jared Diamind the deseases were "developed" by the
>livestock agriculture see: Guns Germs...).
>
>How much faster will *we* be gone? Animal agriculture munches
>10-fold the soil, compared to the ancient direct plant eaters.
>And furthermore we are 10 to 200 as much people as native americans
>were before the invasion.
>
>This isn't a real nutrition topic - but it seems obvious that
>original paleo-style products (wild grown)
>are and will be available only to a small count of humans.
>This applies for plants and animals.
>