Sun, Jul 20, 2003 page9

• Experts dismiss the benefits of tilling the soil

  • By Ben Sandilands / THE OBSERVER
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  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.

  "If we can reduce leakage from farms by 20 percent, this translates to a comparatively easy reduction of 5 percent in global green house outputs," he said.

  "We say it is easy because we don't have to invent any new technology. All we have to do is change the way we till the land, saving on fertilizer along the way," he said.

  The world's largest tractor and harvester manufacturer, John Deere, stunned delegates midway through the conference when it announced a new range of equipment that would help cut the damage done by heavy vehicles to sensitive crop soils.

  The company said it would produce tractor/harvester combinations where the wheels on both would track in perfect alignment, instead of one set of tracks falling inside the other.

  The much smaller British tractor maker JCB started a similar program two years ago.

  "This is an incredibly simple way of reducing degradation by compaction," Tullberg says. "The current type of machine inflicts some degree of damage to about 85 percent of the acreage planted with a crop like wheat."

  "Accurate tracking and better management of the machines cuts this to only 15 percent of land under cultivation," he said.

  The new machines are also designed to use the latest satellite navigation systems accurate to eight centimeters, allowing precision cultivation and harvesting in the worst weather.

  Tullberg says: "The bottom line is that this costs very little, can be done very quickly, and leads to a lasting improvement in the richness of soils, with better crops from less fertilizer."

  "I think this is by far the best fix anyone has come up with for a sizeable part of the global warming problem." he says.

  "But I know other groups of scientists are also working on animal flatulence -- so, if they come up with a means for reducing the amount of methane coming out of cattle, we will be making better progress on climate change than we might have dared to hope for a few years ago," he says.
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