What is it about current agricultural practices that makes them unsustainable? I know there is a reliance on fossil fuels, but that seems like it could be overcome in the long term (1000 years) without needing to move to a decentralized system.
This happens with decentralized farms, too. The problem is not in the kind of farm, but with the techniques used. Tractor tillage increases yields, but is hell on topsoil.
Interesting, thank you. Aquifer depletion seems like a modest problem on a 1k year scale, there's plenty of water around generally. But I hadn't heard of topsoil depletion before; I wonder how difficult it will be to produce it artifically? It sounds like something that will soon be in demand.
There's plenty of water, but aquifers are tend to be tapped in areas with insufficient rainfall/access to rivers.
If you're drawing on the aquifer faster then it replenishes, it'll eventually run out. Sure, it'll replenish itself - eventually - but the land you were cultivating will be unusable for decades. In the meantime, all of your nice topsoil will turn to dust, and blow away.
>I wonder how difficult it will be to produce it artifically?
It's easier to conserve the soil that's already there than to make new soil. That said, there are techniques to increase the production rate of soil. Sheet mulching can create 4 inches of topsoil out of waste organic matter in 2-5 years (compared to thousands of years for natural processes).
Generally it's better to make soil "in place" because moving it breaks up important soil structures, leading to oxidization and nutrient loss.
