LONDON (Reuters) - The world may need new ecological farming approaches besides organic food, embracing technologies which will help feed more people with limited land and water, scientists say.
Organic farming bans the use of yield-boosting, manufactured, inorganic fertilizers as well as industrial pesticides and genetically modified (GM) crops.
Its supporters say the world produces enough food, and the main problems are affordability, accessibility and diets, where meat production uses up more land. They also point to dwindling resources to produce manufactured soil nutrients and an associated rise in costs.
A rise in food prices toward 2008 peaks is feeding a polarized debate on whether African farmers should use non-organic inputs to haul their way out of hunger stoked by that crisis two years ago.
Adding "a reasonable amount" of fertilizer to maize crops in Africa meant "the difference between starving and not only having enough to eat but enough to sell to get some money," said Gordon Conway, at Imperial College London.
"The organic movement has to evolve, to recognize the enormity of the challenge we've got, and look more seriously at sound, sustainable ecological approaches which make minimal use of inorganic fertilizers, industrial pesticides and GM."
That suggestion is disputed by organic advocates who say encouraging more use of such "external inputs," not recycled from within the farming system such as animal manure or leaves, made poorer farmers more vulnerable.
"In a world where those external inputs are going to get scarcer and more expensive it would be the kiss of death to African farmers to do that, not enlightened or sensible," said Peter Melchett, policy director at Britain's Soil Association.
Melchett saw a threat not from stagnant productivity but from relying on fertilizers at a time of dwindling global supplies of natural gas, used to make inorganic nitrogen, and of mined phosphorus.
The International Energy Agency forecast on Tuesday a 10-year global gas glut.
The world population is forecast to grow to about 9 billion in 2050 from 6.9 billion now.
Rising food prices is a global issue, stoking inflation at a time of weak economic growth and deflation fears, and throwing government funding into agricultural research and technology.
European Union state officials met in Brussels on Thursday to discuss the EU executive Commission's proposals to allow governments to decide whether to grow or ban GM crops. Many of the bloc's largest countries have publicly attacked the plans.
Global organic food and drink sales reached $46 billion in 2007, treble 1999 levels, according to organic trade body estimates, which also put the U.S. market at nearly 4 percent of all U.S. food.
A U.N. report in July hailed such growth as an example of market forces valuing the diversity of wildlife. By avoiding pesticides and herbicides, which kill weeds and insects, organic farming fosters biodiversity.
However, some experts cast doubt on those benefits. They say the lower yields of organic agriculture mean if it were adopted more widely the global farmed area would have to rise to compensate, threatening forests on the other side of the planet.
"The sophistication of the argument today is to take into account that trade off," said Tim Benton from Leeds University.
"You give the impression this piece of (organic) land is better, but perhaps the argument that's not been made is if this piece of land is better then somewhere else a piece of land is worse."
He favored a popular "conservation agriculture" approach, where farmers tilled the soil less, if at all, and in that way used less fuel but still used some fertilizer and herbicides.
One emerging ecological technique spreading in Africa is an "evergreen" approach, using a particular tree which sheds its leaves through the maize growing season, fertilizing without shading the crop.
The tree is leguminous, meaning it can produce its own nitrogen, a vital plant nutrient, which it adds to the soil for the crop growing beneath when it sheds its leaves.
"Since we've now developed mass propagation systems we can work with millions of African farmers planting these trees," said Dennis Garrity, head of the World Agroforestry Center, who estimated that 4.5 million African farmers used the approach now and that figure could rise four-fold.
Inorganic fertilizers would complement the approach, which he said also helped trap the greenhouse gas carbon dioxide in the trees, a focus ahead of a U.N. climate conference which starts this month in Cancun, Mexico.
(Reporting by Gerard Wynn, Editing by Janet Lawrence)