earth's fertility

[AnsellTerra]

Is the fertility if the earth less now then it was 300, 3000, or 30,000 years ago? If so are what will happen if the decline continues? And what can we do to stop to or reverse it? I was wondering if anyone knew of anything published about this or anything like it.

[Tim the plumber]

Abstract

Data drawn from a global compilation of studies quantitatively confirm the long-articulated contention that erosion rates from conventionally plowed agricultural fields average 1–2 orders of magnitude greater than rates of soil production, erosion under native vegetation, and long-term geological erosion. The general equivalence of the latter indicates that, considered globally, hillslope soil production and erosion evolve to balance geologic and climate forcing, whereas conventional plow-based agriculture increases erosion rates enough to prove unsustainable. In contrast to how net soil erosion rates in conventionally plowed fields (≈1 mm/yr) can erode through a typical hillslope soil profile over time scales comparable to the longevity of major civilizations, no-till agriculture produces erosion rates much closer to soil production rates and therefore could provide a foundation for sustainable agriculture.

 

http://www.pnas.org/content/104/33/13268.full

 

Yes, we humans have reduced the amount of decent agricultural land on the planet.

 

Mostly by over grazing as well as plowing. The impact of events such as the Arab conquest where nomads conquered area which relied upon irrigation and did not react well to the land being converted into pasture for goats and camels. Carthage harbor silted up in one season after the conquest.

 

The appliance of science will allow us to rebuild such landscapes eventually. The use of crops which do not rely upon the plow will help a lot. Genetic engineering is likely to be the most effective tool to produce such plant species.

[Essay]

Is the fertility if the earth less now then it was 300, 3000, or 30,000 years ago? If so are what will happen if the decline continues? And what can we do to stop to or reverse it? I was wondering if anyone knew of anything published about this or anything like it.

 

…Those are good questions, and a great perspective from which to ask the question about the status of our planet’s health; assuming you’re not asking about ‘fecundity’ or productiveness, but rather asking about the ‘nutrient status’ of the planet.

 

If you take a strictly geochemical view of the planet, and account for 'life' as a geochemical reservoir for salts and metals (the bio-nutrients, not counting carbon or the Hs and Os), then the cycle of nutrients, and their changing availability, both become easier to see.

 

I’ve been studying a path by ‘following the carbon,’ but “follow the nutrients” would probably be a more informative choice.

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I think in general you’ll find that the greater the biodiversity, the greater the accumulation and concentration of nutrients; since life seems to be a concentrator of nutrients, and time can serve as a great accumulator of those concentrations.

 

And of course, rich soils and other sediments can become increasingly concentrated reservoirs for various nutrients, including carbon. Calcium, phosphorus, and iron deposits around the globe are often traced to bioaccumulation, it seems.

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But “good and rich” agricultural soils, fisheries, and forests, is where the ‘availability’ angle becomes important; and where productivity, on a sustainable basis, also needs to be accounted for.

 

“Half of the topsoil on the planet has been lost in the last 150 years.”

“The effects of soil erosion go beyond the loss of fertile land.”

http://www.worldwildlife.org/threats/soil-erosion-and-degradation

And, iirc, according to David Laird; USDA, ARS, National Soil Tilth Laboratory, over 50% of the “carbon richness” in soils has been lost to erosion, globally, over the past few hundred years. That’s a lot of nutrients!

 

 

http://www.nytimes.com/2008/04/29/health/29iht-dirt.1.12423368.html?pagewanted=all&_r=0

 

If the soil does not wash away or get parched by drought, it very gradually thickens. It takes tens of thousands of years to make 15 centimeters of topsoil, about 6 inches' worth.

 

Because of all the things human beings do to it, a University of Washington geologist, David Montgomery, has calculated, the world today is losing soil 10 to 20 times faster than it is replenishing it. In some places it is happening much faster: northern China, sub-Saharan Africa, parts of the American West and Australia are already seeing large tracts of arable land disappear.

 

In his book, "Dirt: The Erosion of Civilizations," Montgomery traces the decline of numerous early societies - including ancient Greece, imperial Rome, various Pacific Island cultures and the Mayans - to poor management of their soil.

 

However, it has also happened that some civilizations have improved their dirt.

 

 

Surprisingly, nutrient-rich, good agricultural soils, only evolved within the past few million years, and are also called "interglacial soils" or mollisols or chernozems (which you can research ...and wonder about where all the nutrients were before those soils evolved to predominate [maybe oceans & forests?]).

 

Nutrients are retained more readily, and for longer, in carbon-rich soils; and so that permitted “some civilizations” to improve the nutrient density of their resources, and sustain themselves longer, and against rougher odds, in general.

 

It will be much easier and rewarding to improve our soils, rather than our crops.

 

Follow the Nutrients!

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