FARMING without synthetic fertilisers could lift the carbon content of Australia's farming soils up to 6 per cent or more.

That's according to organic farming advocate Tim Marshall.

The Organic Federation of Australia deputy chairman is conducting workshops across Australia that explain how.

"The average carbon content of many of our farming soils is now down to 1.5 per cent or even lower, particularly in areas that have dry summers, sandy soils and a long history of cultivation," Tim said at one of the first workshops in Daylesford.

"We are finding that organic farmers are taking their soil carbon content back to 4, 5 and 6 per cent, or even higher.

"They are making those improvements in five to six years in wetter areas. In drier areas it's taking longer."

The news bodes well for organic farming, should Australia introduce a system that rewards farmers for storing carbon and sequestering CO2.

Citing long-term studies from US organic farming research centre, the Rodale Institute, Tim said organic agriculture could sequester 7.4 tonnes of CO2 a hectare a year.

And if the world's five billion hectares of farming land were farmed organically, it could sequester 38 billion tonnes of CO2 a year.

That's one billion tonnes short of the load produced by humans.

He said organic farming worked in several ways to boost carbon content in soils.

Cell grazing was especially good for this. First, it allowed grasses to grow tall. As they grew, their roots lengthened and went deeper, forming air channels.

Deep down, the lignin in the roots was broken down into humus by yeast and fungi. And humus was capable of storing carbon for 1000 to 2000 years.

"The organic matter the fungi add at depth is not subject to the same rapid breakdown by bacterial systems that operate on the surface which leaks CO2 into the atmosphere," Tim said.

Carbon content could also be built up in soils on farms where soils are turned over at shallow levels, not at depth, and where no or low-till systems are used.

Deep tillage broke fungal platforms (the roots or mycelia of fungi) underground.

Left undisturbed, these fungal roots fed nutrients to the roots of plants deep down and extracted carbohydrates for themselves.

"We believe in cultivation, but it's more about loosening the soil and we have some fantastic tools such as shake-aerators and aerators that do this now," Tim said.

He said continuous ground cover helped by allowing roots to establish deep in the soil.

However, synthetic fertilisers such as superphosphate, urea and ammonia, killed fungi and encouraged rapid bacterial breakdown at the surface which in turn sent greenhouse gases into the atmosphere.

Synthetic fertilisers also took a lot of energy to produce, a factor often not considered in energy use comparisons between organic and conventional farming.

Nitrogen fertilisers (urea and ammonia) caused rapid greenhouse gas release from soils, thereby depleting carbon.

Nitrogen fertiliser, for example, exuded nitrous oxide when applied to soils and one nitrous oxide molecule could do the damage of 310 CO2 molecules in the atmosphere.

"If you want to build soil carbon you have to keep nitrogen fertilisers out of your system," Tim said.

"They sponsor a suite of soil organisms that break down carbon matter quickly, releasing CO2 into the atmosphere.

They are not part of the slow breakdown fungal-based systems."

Tim Marshall will conduct further workshops in McLaren Vale (July 29), Naracoorte (August 3), Murray Bridge (August 6) , Mildura (August 13) and Warragul (August 31).

  • For details phone (08) 8339 1250.