THE Federal Government is investigating foreign purchases of city units while ignoring foreign farm raids worth hundreds of millions of dollars.

An investigation by The Weekly Times has revealed foreign companies are assessed when buying an inner-city pad - but could buy a 24,400ha farm with water and not face scrutiny from Canberra.

The revelation comes amid growing controversy over foreign investment in farmland.

As the threshold triggering an investigation into sales of farmland rises from $231 million to $244 million, Federal Treasury has confirmed all foreign persons "must seek approval before purchasing residential real estate in Australia".

Rural independent and Australia Party leader Bob Katter said "every single case" of foreigners buying farmland should be assessed against the national interest.

"It's indicative of the fact that there is no farming interest represented in this place (parliament) now at all," Mr Katter said. "What country would allow this?"

Mr Katter said farming in Australia needed to be "made attractive, so that we won't be selling".

Federal Treasury told The Weekly Times: "Foreign non-residents are generally prohibited from buying existing dwellings in Australia.

"Non-residents seeking to invest in residential real estate can only do so by adding to housing supply and construction activity by either purchasing new housing or developing vacant land. Foreign persons also need to apply to buy or take an interest in vacant land for commercial development."

But a foreign government-owned company could pay $10,000 a hectare for 24,400 ha of farmland without setting off the trigger for an investigation into whether the purchase was in the national interest.

That's 244 square kilometres or 16km x 16km - an area covering the equivalent of Altona to Canterbury and St Kilda to Reservoir.

Dick Smith Foods owner Dick Smith said the monitoring situation was "the opposite of what we should be doing".

"They've somehow got it all mixed up," Mr Smith said.

"Any land we can grow food on, it's absolutely imperative that Australia own that land. If the Chinese government buys a large farming area, they can ship their food directly to China - naturally, that's what they would do."

Federal Liberal MP Dan Tehan said there was "gross hypocrisy" in treating residential property and farm land so differently.

AusBuy chief executive Lynne Wilkinson agreed that it was "stupid and hypocritical".

"We should keep 51 per cent of every major farm there is," Ms Wilkinson said.

Late last month, UK-controlled George Weston (maker of Tip Top bread) and US company Simplot (owner of Edgell, Birds Eye and John West) both slammed the loss of Australia's food bowl to foreign ownership and mining interests.

Meanwhile, mystery surrounds the sale of a third significant tract of land in Victoria's west to an Arab-owned company.

Qatari government-owned Hassad is advertising for managers for a property in northwest Victoria which will be run in conjunction with its other two aggregations in western Victoria.

The latest acquisition of several thousand hectares requires substantial improvement, including cropping, soil development and pasture establishment as well as supporting infrastructure.

Hassad has bought 170,000ha of Australian farmland and plans to spend up to $300 million buying more.

It aims to supply 30-35 per cent of Qatar's food from those farms.

A Hassad spokeswoman declined to comment on which property it had bought, but said Hassad remained committed to farming the land.

Steve Francis, chief executive of Bydand Pastoral Co, which manages Hassad's Australian operations, was unavailable for comment.