As I read the agronomic history of civilization, only the Kayapo Indians (their Terra Preta soils), and the Egyptians (because of Nile floods, now forsaken), have maintained fertility for the long haul at the scale of millennia, one thousand or more cropping cycles.
We are also in "De-Nile" about our own soil carbon loss over time. As technical mitigations like NPK and the green revolution have raised yields, at the same time they degrade soils. One hundred years of synthetic nitrogen has brought soil carbon loss, and even with the best NPK practices, soil carbon loss often continues.
Ten thousand years of civilizations spending their soils, burning forests and mining soil carbon made for a warm and stable Holocene, but now contributing half again as much fossil carbon is destabilizing our future. All that carbon is needed back in the soil.
The true gold standard of a sustainable civilization is soil carbon, measurable soon by earth sensing satellites, available for all to see their good (or bad) works with present and future Google maps like the Soil Carbon Coalition's Atlas of Biological Work: http://soilcarboncoalition.org/atlas
The clarity and simplicity of this perspective has focused my efforts to this goal, my Holy Grail, political and financial recognition of soil carbon content. Penalties for CO2's externalized cost and rewards for soil carbon’s climate values.
Every gram of additional soil carbon holds and returns eight grams of water. The old Chinese proverb comes to mind: “Despite our artistic pretensions, sophistication, and many accomplishments, humans owe our existence to a six-inch layer of topsoil and the fact that it rains.”
Erich Knight (guest editorial)