Sun, Jul 20, 2003 - Page 9 News List

Experts dismiss the benefits of tilling the soil

By Ben Sandilands  /  THE OBSERVER , CANBERRA

The world's top soil scientists met on the rich granite plains west of Brisbane, Australia, this week to over turn some long cherished farming practices.

They examined physical proof that the annual cycle of digging up soil to plant crops and spread fertilizer was robbing farmers of higher incomes and harming the environment.

Delegates to the special session of the International Soil Tillage Research Organization (ISTRO) saw alternative techniques that could cut man-made greenhouse emissions by as much as 5 per cent in as little as five years.

Jeff Tullberg professor of soil sciences at the University of Queensland, Australia, and president of ISTRO, described the changes as both simple yet dramatic in terms of methods and benefits.

"It has been held since time immemorial that breaking or tilling the soil was essential to let it `breathe' and make it more fertile," he says.

"But many soil scientists around the world have questioned that, and now all the data has come together to make the case to the contrary."

Tullberg says this excessive tilling means the soils `exhale' far more carbon dioxide and nitrous oxide than they would in a natural or non-farming cycle of growth and decay.

Both gases contribute significantly to the greenhouse effect which has been linked to global warming and the outbreak of wild weather across the planet.

While nitrous oxide is created naturally in swampy soils, its leakage from fields is multiplied by the breakdown of nitrogenous fertilizers and the engine emissions of large farm machines.

"Essentially, what we have done on our farms is to make our fields give up a surplus of greenhouse gases that would otherwise have remained locked in the ground," Tullberg said.

"We have also been able to prove that the excessive leakage of these gases renders the soil less fertile over time." he said.

According to the papers presented at the conference, the key to the soil fertility is worms, which are all too often wiped out by overuse of fertilizers and pesticides -- and by being dug up.

"Worms open up soils for water, air and nutrients. They make it store more water and they load the earth with carbon-rich organic material," Tullberg said.

"The concept that untilled soil will turn to rock-hard clay is only true if there are too few worms, and too much compacting of the soil by the wheels of heavy tractors and harvesters," he said.

"This has brought us to the second reason for the problem, excessive traffic over our crops," he says. "We have now demonstrated that, by reducing heavy traffic and minimizing digging, and spreading the right composts over the surface, we can lift the worm population up eightfold."

The soil scientists emphasized that the carbon dioxide and nitrous oxide concentrations in the atmosphere are continually created by natural and industrial processes and circulated in the atmosphere before being cycled back into the soils and oceans.

But in modern times these cycles have become unbalanced, creating rising concentrations of greenhouse gases last found in the atmosphere during the intense episode of global warming that preceded the onset of the last ice age, about 130,000 years ago.

Tullberg says the consensus on the proportion of man-made greenhouse gases from agriculture is about 25 percent of the total, with the rest emitted by cars, heavy industry, and the use of fire and machines to clear vast tracts of forest.

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