Charcoal may hold key to boosting soil and output

Countryman
Thursday 6/3/2008 Page: 48

Want to grow more wheat with less fertiliser, in a drier climate and get a bonus for carbon credits at the same time? It seems like pie-in-the sky, but it may be on the cards if trials using charcoal as a soil amendment fulfill their early promise. Biochar is fine-grained porous charcoal, made from wood or any biological material (even manure) that has been pyrolised (heated without oxygen to about 450 degrees C) so that mainly carbon is left.

Pyrolysis produces a net surplus of energy that can be used to generate electricity as at the Verve integrated wood processing demonstration plant at Narrogin. Biomass growth followed by Pyrolysis it is one of the few energy production systems that are carbon negative (they extract CO2 from the air). Others such as wind power or solar energy are carbon neutral at best. *

Biochar has some interesting attributes: it lasts a long time in the soil, it absorbs and slowly releases water and nutrients to plants, reduces soil acidity and provides a safe home for beneficial soil organisms. What is more, it is relatively cheap to produce. Biochar is also very stable in the soil. Researchers think biochar contributed many years ago to the dark fertile terra preta soils of the Amazon basin and the chernozems of Russia and the Ukraine. Chernozems are a very black topsoil, rich in humus, typical of cool to temperate semiarid regions, such as the grasslands of European Russia.

If you grow oil mallees, harvest them, extract the valuable cineol-rich oil by steam distillation and pyrolyse the residue you get biochar. Biochar contains around half of the biomass carbon in the oil mallees. The net result is you have removed large amounts of carbon from the atmosphere. When carbon trading arrives in Australia, biochar is worth money because businesses that emit excess carbon dioxide will have to purchase carbon credits to make up the difference.

Biochar effectively sequesters large amounts of atmospheric carbon, creating carbon credits. WA has the capacity to produce more than nine million tonnes of biochar a year. Once the biochar has been produced you could store it as sequestered carbon and make money from the carbon credits, or you could use it as a soil amendment.

Dr BlackWell, soil research officer with the WADAF, said trials at Pindar and Kalannie had shown increased returns from wheat of up to $96/ha, especially when biochar was applied with mineral fertilisers and inoculated with beneficial soil micro-organisms. "The results were mainly driven by water supply," he said. "The wheat was planted on 60cm wide rows. It is very early days to make predictions about the effect of soil charcoal on yield." In the trial the DAF applied 2-3 tonnes/ha of biochar deep banded in an acid sandy clay loam through an airseeder, before break of season.

When wheat was sown using the same tramlines, arbuscular mycorrhiza (AM) tripled their colonisation of wheat roots. In infertile soils AM live symbiotically with plant roots, harvesting nutrients such as phosphorus and zinc. In return they receive carbohydrate from the host plant. However, in fertile soils AM may tend to act parasitically. Charcoal also appeared to make wheat more drought-tolerant, possibly because the AM reduced drought stress.

Mr Kerkman's autosteer system allows him to place his wheat seeds within two centimetres of the biochar. "It will give rise to a new sustainable farming industry," he said. "Charcoal increases yields 5-10 per cent and reduces fertiliser needs by 40 per cent." "You need charcoal to tame the vicious soils of Australia, and if we can use charcoal we could be paid to do it," said Mike.

The problem is getting the initial investment to build a carboniser. Mr Kerkmans estimated a capital cost of $6.5m for the plant. "We also need a carbon-emitting company to pay farmers for carbon credits," he said. Dr BlackWell said much more research was needed on the long-term effects of incorporating biochar as a soil amendment in different soils and climates. Moreover, costs of manufacturing and applying charcoal and any carbon credit benefits were at present unknown. "I don't want people to get excited about the results and then be disappointed," he said.

* This is incorrect. Once a solar panel or wind turbine has produced energy exceeding the amount used in its construction, it is clearly carbon negative. Blair.