FARMERS have cautiously welcomed the sharp slump in the Australian dollar, which could deliver them a $1.7 billion export bonus.

During the past two weeks, the dollar has plummeted 9 per cent against the US "greenback", dropping from about US90c to less than US83c early this week. Yesterday morning, it was trading at US82.6c.

Most of the slump has come in the past 10 days, as the Greece-related European debt crisis has seen "safe havens", including the US dollar, benefit at the expense of currencies seen as riskier, including the commodity-driven Aussie dollar.

"It's been an unexpected boost for Australia's farmers," National Farmers' Federation economics policy manager Charlie McElhone said.

"It'll be a massive leg-up if the currency stays that low. But the big question is: will it last?"

The NFF calculates that every 1 per cent drop in the dollar against the US dollar adds about $195 million to farm bottom lines if it persists for 12 months.

A lower dollar boosts export returns, which more than offset the higher cost of imported farm inputs. It also helps with longer-term competitiveness by making Australian exports cheaper overseas.

Dairy Australia's strategy and knowledge manager Joanne Bills said there were benefits for dairy producers, particularly in Victoria, South Australia and Tasmania, which were linked closely to the world market.

"On the face of it, a weaker dollar is good for the dairy industry," she said.

But Ms Bills said there was a lot of uncertainty and it was important to work out what was driving the dollar down.

"It's really hard to untangle the fundamentals behind such a massive slump," she said. "If it reflects a view that the world economy is about to slow down, then this could be bad for commodity prices.

"But most dairy companies will be organising some sort of coverage at this low dollar, so there'll be benefits no matter what happens from here on."

AWB Limited spokesman Peter McBride said the dollar slump was good for wheat exports.

"It's early days, but if the dollar stays low, our wheat will be more competitive," he said.

The lower dollar has already cushioned grain growers against a big drop in world wheat prices.

Chicago Board of Trade prices have fallen $US15.80 a tonne in the past two weeks while, in Australian dollars, the CBOT contract price is down just $6 to $207 a tonne.