Farmers used to growing grain or raising livestock are being urged to consider algae as a farm crop.

Science writer Julian Cribb says it is an essential future industry.

Mr Cribb has presented his idea to the International Rural Network conference at Whyalla in South Australia, saying algae farming can provide fuel and the food supply for fish farming.

He said it was being done overseas but yet to be embraced in Australia.

"We need to double food production worldwide to feed 10 billion people by about the 2060s," he said.

"The trouble with that is that everything we need to double food production is running out."

He said essential elements of food production, such as fresh water, available land, fertilisers and stable climates were in decline.

But Mr Cribb said algae could be a way forward.

He said it could be cultivated in states such as South Australia with sunlight, large areas of flat land and use of salt water.

"People in Australia need to realise that we've got the largest resource of sunlight on Earth," he said.

"Sunlight grows crops, it grows things like algae."

Mr Cribb said each hectare of algae could produce 50-100 barrels of oil.

"You could probably grow the whole of South Australia's liquid fuel requirements," he said.

"That's [for] every car, every truck, every ship, every train and every plane from an area no bigger than a single large sheep station."

Aquaculture boost

Mr Cribb said aquaculture could achieve huge benefits.

"To feed those fish you're going to have to grow algae because it's going to be too expensive to feed them on grain," he said.

He said fish farming could help overcome depletion of fish numbers in the oceans.

"The world catch has been declining every year since 2004. We've already gone through the oceans," he said.

Mr Cribb said people would need to change their diets and embrace species best suited to farming.

"You can get 10 tonnes of barramundi from one hectare of pond, so it's a very high-yielding and highly-productive industry," he said.

"South Australia's already very good at farming fish, but the future aquaculture industry is going to be worth $5 billion - it's going to be bigger than beef, sheep, pork and poultry put together."

Mr Cribb said countries such as Israel, China and the United States were already embracing algae for fuel production.

He said algal fuels were being used by the US air force and navy.

"There was a big American military exercise about a month ago where every plane that took off from an aircraft carrier was fuelled by algae," he said.

He said imagination and investment would allow an industry to develop and expand in South Australia.

"We need the imagination to understand that South Australia is actually the best place in the world to do this because you've got open skies and more sunlight than almost anywhere in Australia," he said.

"There are a lot of very innovative farmers in SA and I think some of them would think about growing water crops, beside growing land crops.

"That is the opportunity of the future, instead of the big oil companies drilling for stuff, it is for farmers to actually grow it."