Agrichar – saving the planet with black earth

Trials in Australia have suggested a way to both fight climate change and improve the fertility of carbon-depleted fields. According to new research findings by the New South Wales Department of Primary Industries, Agrichar, a black carbon by-product of pyrolysis, has tripled wheat yields when applied to fields in Australia. It has been newly hailed as the saviour of Australia's carbon-depleted soils, which have reduced yields due in part to limited amounts of the element.

Pyrolysis is a process where biomatter is heated under pressure in an environment devoid of oxygen. In fact, pyrolysis goes on in everyday cooking processes, including frying, roasting and baking. The middle of your food cooks but doesn't burn because the outer layers keep oxygen out. On an industrial scale, the pyrolysis of waste biomatter is attracting interest because it is a source of renewable energy.

The three constituents of the product mixture are a fuel gas composed mostly of methane and hydrogen, an oily liquid mixture that can also be used as a fuel, and the char, which has been shown to be an effective fertiliser and stable carbon sink. Different pyrolysis procedures can give a different mixture of products. Because of the absence of oxygen in this process, no carbon-dioxide gas is given off in the process. The man most strongly advocating the use of pyrolysis-based technology in Australia is Tim Flannery, a scientist, conservationist and writer who won the Australian of the Year award for 2007. As reported in The Bulletin magazine, he ranked fostering pyrolysis-based technologies' as fourth in his five steps to save the planet, and it's not difficult to see why.

According to Doctor Lukas Van Zwieten, a researcher at the NSW Department of Primary Industries, soils turn over 10 times the amount of greenhouse gases than the burning of fossil fuels on a global scale. Soils are one of the planet's most important carbon sinks, and need to provide us with food to feed a growing human population, so increasing carbon storage in soils is a way of killing two birds with one stone.

Carbon in soils is described either as stable' or labile', depending on how quickly it is converted to carbon dioxide gas by natural chemical processes. Most carbon applied to soils, in the form of mulch and compost, for example, lasts only two or three years, whilst agrichar will remain in the soil unchanged for hundreds of years. This makes it a good tool for carbon sequestration as well as a good source of stable carbon for fields. For farmers, one application of agrichar may well serve as the equivalent of several applications of normal' fertilisers. This is partly because the material doesn't just add carbon, but also changes the retention time of other elements, such as phosphorous and calcium. Using agrichar could save farmers money, and help ensure local environments aren't adversely affected by agricultural over-use of fertilisers. In terms of soil greenhouse gas emissions, the study found that emissions of carbon dioxide and nitrous oxides (another important greenhouse gas) from the agrichar enriched soils were significantly lower'.

Other benefits of agrichar as a fertiliser are that it raises the soils pH, improves water-holding capacity and soil biology, and even reduces aluminium toxicity in some soils. The fertilising power of such materials can be seen not only from the results of this study, but in the Amazon Basin, where similar substances have been enriching soils for thousands of years. There is some discussion as to whether this dark earth' or 'terra preta' was intentionally used to enrich soil or whether it was simply a by-product of habitation. If it was intentionally added, it would be amazing to see that technologies we are only now experimenting with have been used in another form for thousands of years. In the amazonian rainforest, terra preta is incredibly productive, despite being intensively cultivated, and has been shown to contain more than five times as much carbon as surrounding soils. In some ways, the test for this science has already been carried out for us.

Unfortunately, agrichar is presently very hard to come by. Industrial pyrolysis is currently pioneered by ONLY a handful of Canadian companies, including Agri-THERM and Dynamotive. BEST-energies, in Australia, has a pilot plant and produced small amounts of agrichar for the purpose of this research. Even if agrichar is an attractive alternative to conventional fertilisers among farmers, they will have to wait until pyrolysis becomes popular as a source of energy or fuel, before, as a by-product, it will become widely available.

Van Zwieten is optimistic, hoping that, "the technology will take hold and pyrolysis plants will be built where there is a steady stream of green or other biomass waste providing clean energy that is carbon negative".

Soils offer new hope as carbon sinks', may 2007 provided by New South Wales Department of Primary Industries, http://www.eurekalert.org/pub_releases/2007-05/nswd-son053107.php

1 for a more detailed look at the procedure of slow pyrolysis and technology involved, take a look at the BEST-energies at http://www.bestenergies.com/companies/bestpyrolysis.html

- Written by Ben Griffin-Smith

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