SYDNEY -- The world's over-farmed soil is sick and has been rapidly getting sicker, but scientists say space-age, satellite-driven tractors are coming to the rescue.

Heavy modern farm equipment is killing the soil through repeated compaction and tilling, which in turn worsens salinity that kills crops. But a new world of automatically steered tractors, guided by satellites, will allow them to run on pre-determined tracks and confine their impact on the soil to 15 percent of farmed land.

"It will revolutionize agriculture, I believe," said Jeff Tullberg, a University of Queensland academic and president of the International Soil Tillage Research Organization (ISTRO).

Tullberg was speaking from an ISTRO conference of 220 world scientists in Brisbane, which this week showcased Australian technology for satellite-guided field equipment to an accuracy of two centimeters, or less than an inch.

U.S.-based farm equipment leader Deere & Co also followed an early Australian lead to develop an integrated tractor guidance system based on global positioning system (GPS) satellite technology, accurate to centimeters.

Space-age tractors, first produced with Australian technology only a couple of years ago, are becoming increasingly popular and are leading a revolution aimed at saving the world's soil -- as well as boosting farm incomes. Scientists say the world's soil is sickest in the farmlands of the developed world in North America, Europe and Australia.

This is because the soil is being repeatedly run over by 20-tontractors, then plowed up to break hard surfaces. Groundcover gets pushed beneath the earth and a hard surface re-forms on top.

Rainwater runs off the surface or gurgles down cracks into subterranean salt and water tables, which rise to the surface.

"Considering that water is the most valuable resource the Australian farmer has, this is crazy stuff," Tullberg said.

One of the biggest farm exporting nations in the world, Australia is at the forefront of a drive to take broad-scale agriculture back to the precision of peasant farming.

A system confining tractor wheels to established lines without tilling is now operating on one million hectares (2.5 million acres) of Australian farmland, out of the 20 million ha devoted to major crops.

About 500 tractors have been equipped with satellite guidance systems in Australia, about the same number as in the United States, despite the extra cost of up to A$50,000 ($32,500) on a A$150,000 bill for a conventional tractor.

Farmers speak of yield increases of up to 200 percent through improved water filtration, storage and more uniform content across the field, together with possible double-cropping. Space-age tractors also save money through eliminating overlaps and allowing farms to work at night. ($1=A$1.54)