Massive changes in farming practices, eating habits and consumption will be needed to feed Earth's population sustainably when it hits nine billion in 2050, French scientists warned on Wednesday.

In under 40 years, the world will have to make farming more productive but less dependent on harmful chemicals, curb food losses and waste, protect the environment and reduce agriculture's exposure to disastrous price swings, they said.

Their study, called Agrimonde (Agriworld in French), is co-authored by specialists at France's National Institute for Agricultural Research (INRA) and the International Cooperative Centre for Agronomical Research for Development (CIRAD).

"This exercise is undertaken at a very specific human history, at a time when the population today is seven billion," CIRAD president Gerard Matheron said at a press conference. "World agriculture faces a major challenge."

Last week, the UN's Food and Agriculture Organisation (FAO) reported that food prices had hit their highest level ever and World Bank President Robert Zoellick warned that rising prices for staples "are re-emerging as a threat to global growth and social stability."

Riots in Algeria, meanwhile, left five people dead, hundreds wounded and about 1,000 in jail, prompting the authorities to promise to cut food prices.

The Agrimonde study said that North Africa and the Middle East, Asia and sub-Saharan Africa, all with fast-growing populations today, will be heavily dependent on imported food in 2050.

It puts forward two scenarios -- both relatively optimistic -- by which the planet's expected nine billion humans are fed by 2050.