Archive for the ‘terra preta’ Category


Carbon return desk II

August 27, 2006

So, as I posted a couple of days ago, the standard – and surprisingly well developed – technique for carbon sequestration is to stick it way under the ground, in deep aquifers.

But there’s another contender out there accruing its fan base: sticking it onto the ground.

More specifically, there are marvelously productive soils out there, typified by the terra preta of the Amazon, which are a couple of feet deep and which turn out turnips and whatnot twice the size of those that come up in ordinary soil. It turns out this class of rich black earths is anthropogenic. Armed with the right know-how, any farmer or gardener can have it. And fight global warming withal.

The chief evangelist for terra preta was the late peripatetic Dutchman Wim Sombroek. As Nature reported on August 10:

Sombroek was born in the Netherlands in 1934 and lived through the Dutch famine of 1944 — the Hongerwinter. His family kept body and soul together with the help of a small plot of land made rich and dark by generations of laborious fertilization. Sombroek’s father improved the land in part by strewing it with the ash and cinders from their home. When, in the 50s, Sombroek came across terra preta in the Amazon, it reminded him of that life-giving ‘plaggen’ soil, and he more or less fell in love. His 1966 book Amazon Soils began the scientific study of terra preta.Since then trial after trial with crop after crop has shown how remarkably fertile the terra preta is. Bruno Glaser, of the University of Bayreuth, Germany, a sometime collaborator of Sombroek’s, estimates that productivity of crops in terra preta is twice that of crops grown in nearby soils

Sure enough, the Brazilian soils had been built up by Brazilian locals over centuries, with bone and manure and – chiefly – charcoal, which is the source of the black color. For a sense of the soil’s productivity, compare the photo of preta corn on the left, normal soil corn on the right, and like they say in the Sure commercial, your left side will convince your right side.The charcoal tends to absorb water and assorted nutrients that would otherwise sink into the aquifer. That in turn encourages massive growth of microorganisms, who not only further enrich the soil, but bind an astonishing quantity of carbon in subsoil biomass. Three feet of terra preta, it is claimed, will support a biomass equal to the rain forest above the same ground.

Expertise is still slim (What’s the optimal mix of char with other ingedients, and how does it change with climate? How compatible is formation of these soils with other green practices like no-till farming?), but it’s growing. In addition to the Bayreuth project, Danny Day runs a working production facility in Athens, Georgia, which turns farm waste like peanut shells half into biofuels and half into char. Free hydrogen is another byproduct. At Iowa State University Ames, Robert Brown is doing something similar with corn rather than peanuts. In New South Wales, Biomass Energy Services and Technology has constructed a series of char-producing engines at increasing scales.

The bottom line? Brown estimates that the U.S. corn crop alone could be used to sequester a quarter of a billion tonnes of carbon a year.