Australia's conservative opposition on Friday earmarked tighter scrutiny of foreign investment in agriculture as a priority if the party is elected to government next year as recent polls suggest.

Rural conservative politicians have recently warned against selling valuable agricultural land to foreign investors, particularly China which is Australia's top trading partner due to bullish resources exports.

Opposition leader Tony Abbott said while he welcomed foreign investment, Australia needed to improve oversight when it came to farming land and agribusiness, as the party released a policy paper on the subject.

"I want to make it absolutely crystal clear that the (opposition) coalition unambiguously supports foreign investment in Australia," Abbott said.

"We need it, we want it, it is essential for our continued national prosperity ... what's very important though is that the public have confidence that the foreign investment we need and want is in Australia's national interest."

The policy paper called for the Foreign Investment Review Board to consider any proposed foreign acquisition of agricultural land valued at more than Aus$15 million (US$15.7 million).

It also demands any proposed foreign purchase of an agribusiness of more than Aus$53 million be scrutinised.

It notes "growing community and industry concern that some types of acquisitions may be contrary to the national interest and that a strengthening of the regime may be advantageous to the long-term prosperity and food security of Australia".

A government study into ownership of Australian agriculture published in January found that foreign firms controlled about half of the nation's key food industries but offshore investors owned just 11 percent of its farmland.

The opposition paper follows a speech by Abbott in China last month in which he said it would rarely be in the national interest to allow a foreign government to control an Australian business, comments the government dismissed as "dangerously dumb".

China is Australia's number-one export market and its top source of imports, with two-way trade worth Aus$113.7 billion in 2011.

The two nations were reported in May to be in talks about direct Chinese investment to develop northern Australian farms focused mainly on beef, sheep, sugar and dairy, in a bid to boost food security.

Treasurer Wayne Swan said the opposition's plan was a "muddle".

"The truth is the government has a very strong set of national interest guidelines which govern state-owned enterprise investment in Australia," he said.