Small world. I started reading "Our Good Earth," Charles Mann's superb National Geographic story on dirt because Tyler Cowen called it "one of the best magazine pieces of this year." I certainly wasn't expecting the cameo appearance made by Yacouba Sawadogo, a farmer in Burkina Faso I wrote about two years ago, in "A Tree Grows in the Sahel."

Sawadogo's story was fascinating because using a decidely low-technology technique for increasing soil fertility -- zai holes -- he managed to bring forests back to what had been horribly degraded land.

Sadly, Mann updates the tale with a tragic postscript.

To provide income for Burkina's cities, the central government let [landowners] annex and then sell land on their peripheries -- without fairly compensating the people who already lived there. Sawadogo's village is a few miles away from Ouahigouya, a city of 64,000 people. Among the richest properties in Ouahigouya's newly annexed land was Sawadogo's forest, a storehouse of timber. Surveyors went through the property, slicing it into tenth-of-an-acre parcels marked by heavy stakes. As the original owner, Sawadogo will be allotted one parcel; his older children will also each receive land. Everything else will be sold off, probably next year. He watched helplessly as city officials pounded a stake in his bedroom floor. Another lot line cut through his father's grave. Today Yacouba Sawadogo is trying to find enough money to buy the forest in which he has invested his life. Because he has made the land so valuable, the price is impossibly high: about $20,000. Meanwhile, he tends his trees. "I have enough courage to hope," he says.

Mann's exploration of dirt, which finds him traveling from China to the Sahel to the Amazon to a Wisconsin farm technology fair, is rich with discomfiting observations: "Connoisseurs of human fecklessness will appreciate that even as humankind is ratcheting up its demands on soil, we are destroying it faster than ever before," he writes, and then proceeds to show how Chinese peasants and big Wisconsin farmers are equally guilty of ravaging the land upon which we all depend for sustenance.

But it isn't all doom. Mann closes his story with a titillating look at the possibilities of man-made "terra preta," the charcoal-infused soil discovered in South America that predates Columbus, but is still remarkably fertile. Terra preta is the ultimate kill-two-birds-with-one-stone killer agricultural app: We may be able to take carbon, bury it in the ground, and increase both soil fertility and the earth's carbon dioxide sequestration capabilities.

It won't be easy -- but no one ever said feeding 9 billion people on a quickly eroding planet would ever be easy. And it won't be glamorous -- soil science isn't one of the prime-time Olympic showcase domains of technological innovation.

But it is critical. As Mann makes clear: It's all about the dirt.

UPDATE: I've corrected a reference to burying "carbon dioxide" in the paragraph on terra preta.