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Semedo, head of the UN's Food and Agriculture Organization, claims in the linked article that "generating three centimeters of top soil takes 1,000 years." But
by philipkglass 9y ago
Semedo, head of the UN's Food and Agriculture Organization, claims in the linked article that "generating three centimeters of top soil takes 1,000 years."
But the organization says of topsoil formation on its own web site:
The rate of topsoil formation can vary from < 0.25 mm/year in dry and cold environments to > 1.5 mm/year in humid and warm environments (Hammer 1981; Hudson 1981). Topsoil formation at the rate of 1 mm/year is equivalent to an annual addition of 12 t/ha. Therefore, the rate of topsoil formation has been considered as a factor in the model in assessing loss of productivity and tolerable soil losses.
http://www.fao.org/docrep/009/t0733e/T0733E06.htm http://www.fao.org/docrep/009/t0733e/T0733E06.htm
1 mm/year means 30 years to generate 3 cm of topsoil, not 1000 years. And human intervention can increase productive topsoil rather than deplete it, when the incentives are properly aligned.
I don't know if the 1000 years figure is a mistake, based on newer, more pessimistic measurements of soil formation rates, or something else.
- milesvp 9y agoI can tell you the units you supplied are off. You need at least 2 more dimensions to get a volume of topsoil, otherwise it's a meaningless number. do they mean 3cm^3 of topsoil, because I guarantee that doesn't take 1000 years. Is it 3cm*earth_surface_area in a thousand years. Maybe... but my understanding is topsoil by erosion is the slowest way to get topsoil. I read a paper some years ago on biopurturbatuon, which changed my thoughts on topsoil mining. Basically worms, root structures, and other organisms are very good at creating topsoil. So you could very much produce huge amounts of the stuff in human time spans if the economic incentives were there. It was an interesting paper, and I wonder if it didn't gain much traction, or was heavily refuted. If I was more cynical, I'd think Semedo was purposely ignoring it for political reasons.
- philipkglass 9y agoThe units are for depth, similar to how precipitation is reported in mm. Naturally you'd also need to know the relevant area to find total volume.