SCIENTISTS are demanding that governments protect valuable agricultural soil under threat from Adelaide's urban sprawl.

Retired government soil scientist James Hall said the state needed to be "a bit more clever about what we do and maybe target other areas".

"This continual spread of Adelaide really needs to stop," he said.

"Although the Government is pushing towards building up within Adelaide, rather than spreading out, it is still spreading."

He said the state's top five areas, with special soils worth protecting, were the Barossa, McLaren Vale, Adelaide Hills around Lenswood, Northern Adelaide Plains, and lower North around Freeling, Roseworthy and Kapunda.

Mr Hall said he was the only soil scientist left in the "huge" Environment Department when he retired earlier this month.

The Australian Society of Soil Science will target planners, policy-makers and natural resource managers at the Land Use Symposium 2012 in Adelaide today. Mr Hall, who organised the symposium, will share his knowledge from 22 years experience mapping soils for the State Government.

He said the plan for Monarto, developed in the early 1970s, was "fantastic" because it was "not tremendously good agricultural land, not far from Adelaide and not far from the eastern states".

"If we had something like that now, that would be taking the pressure off Adelaide," he said.

Society state president Dr Annie McNeill, senior lecturer in soil science at the University of Adelaide, said the lack of technical expertise in soil mapping within the Government was disturbing.

"We do really need to understand the value of these soils," she said. "They underpin all these different agricultural landscapes, landscapes important economically for South Australia: The wine industry, broadacre cropping, horticulture, all of those things are what South Australia is famous for really, not just from an industry point of view but from a tourism point of view, too."

Dr McNeill said most people would rather have their apples come from Lenswood than put housing across the horticultural soils and bring apples in from New Zealand.

"People don't understand that soil is probably our greatest asset, our greatest resource," she said.

Originally published as Endless sprawl a threat to soil