Wednesday, November 26, 2008

The True Value of Soil Carbon

Carbon trading systems must be careful not to undervalue soil carbon, according to a leading soil scientist, because the true productivity value of soil carbon to farmers may be hundreds of dollars per tonne.

Dr Rattan Lal, a professor and director of the Carbon Management & Sequestration Center at Ohio State University, was a keynote speaker at last week's Carbon Farming Conference in Orange, NSW, hosted by the Carbon Coalition. He indicated that in order to commoditise carbon, a realistic value must be established that reflects its value to farmers and society.

When Dr Lal looked at humus, of which carbon is the main component, and teased out the nutrients and water typically held within a kilogram of humus, he arrived a value of US$250 a tonne on today’s prices. BUT…..initial estimates of carbon's starting value under the Australian Carbon Pollution Reduction Scheme (CPRS) are around $20 per tonne. That is a big disparity!

Farmers, and society at large, also benefit from the fact that soils with high levels of organic carbon (humus, as shown in the photo) are resistant to erosion, deliver less pollution to waterways, biodegrade chemical pollutants and buffer climatic extremes.

"Whether the trading process can provide farmers with all of that value remains to be seen, but undervaluing a resource can lead to its abuse " Dr Lal told the conference via an internet video link.
If soil carbon ultimately earns a high price, it raises questions about the value and use of crop residues that contribute to soil carbon formation. Cellulosic ethanol plants that will draw on crop residues are being built in the United States, and the technology is under discussion in Australia.

However, Dr Lal observed that the world's estimated four billion tonnes of annual crop residues should play an important part on the farming process. In Dr Lal's estimation, those global residues contain 30 million tonnes of nitrogen, 3.5mt of phosphorus and 47mt of potassium—and crop residue contains about 40pc carbon.

His initial studies were mainly concerned with conservation tillage and use of crop residues for erosion management in the tropics. Attempting to increase the cover component of the Universal Soil Loss Equation, in effect, and improving establishment. It worked! But the use of residues also improved the soil carbon levels, in the medium and longer term. That improves soil quality.

With residue left in the field rather than removed, soil carbon levels were 0.2pc higher, soil pH was 5.1 under residue and 4.6 without, and that corn yields on a field sown into residue were 2.7t per hectare compared to 1.5t/ha in a bare field. This data is based on studies of crop residues in a Nigerian corn system. Soil quality is significantly influenced by residue retention. There are also additional studies from both temperate and tropical areas that draw the same conclusions.

Dr Lal has also extrapolated how improving soil carbon might affect food security for the 854 million people currently considered "food insecure". In 2000, the global food deficit was considered to be 13 million tonnes; by 2010, this will have risen to 22 mt, mostly in sub-Saharan Africa. By increasing soil carbon levels in the 532 million hectares of agricultural soils in developing countries by a modest one tonne per hectare per year, Dr Lal calculated an extra 30-50mt of food could be produced per year.

This is a potent message and adds to increasing pressure to better use the millions of kilograms disposed of as recycled organic material in Australia each year. While there are some logistical issues in returning this material to rural areas for use, they need adressing to ensure the material is used effectively.

Soil carbon is vital.......ensure there is more of it!

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