Terra Preta soils - can the NT reach this level of improved soil carbon

Terra Preta: Black is the New Green

Carbon sequestration faces some major hurdles. Technical geosequestration methods could pump large amounts of CO2 deep underground but are still under development. On the other hand, natural methods that store carbon in living ecosystems, such as trees, may be possible in the short term but require huge swathes of land and are only as stable the ecosystems themselves. An ideal solution, however, would combine the quick fix of biological methods with the absolute potential of technical ones. Terra preta [sometimes seen as terra petra] may do just that, as a recent article in the journal Nature reveals. Soil sequestration of carbon has many proponents, incluidng a number of very experienced and knowledgeable scientists, in numerous countries. Australia has been slow to solidly examine this option, yet our soils - some of the oldest and most depleted on planet earth, could really get a kick start with higher soil carbon levels.

Amazonian Dark Earth, or "terra preta do indio", has mystified science for the last hundred years. Three times richer in nitrogen and phosphorous, and twenty times the carbon of normal soils, terra preta is the legacy of ancient Amazonians who predate Western civilization. Scientists who long debated the capacity of 'savages' to transform the virgin rainforest now generally agree that indigenous people transformed large regions of the Amazon into amazingly fertile black earth. The Amazonians' techniques remain an enigma but are believed to have used slash-and-smoulder to lock half of the carbon in burnt vegetation into a stable form of biochar instead of releasing the bulk of it into the atmosphere like typical slash-and-burn practices.

The difference between terra preta and ordinary soils is immense. A hectare of metre deep terra preta can contain 250 tonnes of carbon, as opposed to 100 tonnes in unimproved soils from similar parent material, according to Bruno Glaser, of the University of Bayreuth, Germany. To understand what this means, the difference in the carbon between these soils matches all of the vegetation on top of them. Furthermore, there is no clear limit to just how much biochar can be added to the soil.

Claims for biochar's capacity to capture carbon sound almost audacious. Johannes Lehmann, soil scientist and author of Amazonian Dark Earths: Origin, Properties, Management, believes that a strategy combining biochar with biofuels could ultimately offset 9.5 billion tons of carbon per year-an amount equal to the total current fossil fuel emissions!

Indeed, there is profit to be made in this black earth, for if green is the new black, then black could be the new green. Biofuels are touted as 'carbon neutral', but biofuels combined with biochar [ now generally referred to as agrichar] together promise to be 'carbon negative'. There are a number of competing technologies and some have fuel oil as a potential product, with agrichar the byproduct.

One technology - the Eprida technology uses agricultural waste biomass to produce hydrogen-rich bio-fuels and a new restorative high-carbon fertilizer (ECOSS) . Trials in tropical or depleted soils with ECOSS fertilizer sustainably improves soil fertility, water holding and plant yield far beyond what is possible with nitrogen fertilizers alone. The hydrogen produced from biomass can be used to make ethanol, or a Fischer-Troupsch gas-to-liquids diesel (BTL diesel), as well as the ammonia used to enrich the carbon to make ECOSS fertilizer. Ecocarbons from Australia have another system, with Dynamotive Energy Systems of Canada also in the mix.

Terra preta's full beauty appears in this closed loop. Unlike traditional sequestration rates that follow diminishing marginal returns-aquifers fill up, forests mature-practices based on terra preta see increasing returns. Terra preta doubles or even triples crop yields. More growth means more terra preta, begetting a virtuous cycle. While a global rollout of terra preta is still a long way off, it heralds yet another transformation of waste into resources.