Food quantity or food quality? Can the world quell starvation now and still have a healthy ecosystem over the long term?

Tough questions for anyone concerned about agriculture and its relation to hunger and poverty.

In a keynote speech at the World Food Prize symposium today, Bill Gates said he supports sustainable agriculture, welcome words to experts in the field, who say there is no short term fix.

Much as he changed the landscape on health, the world's richest philanthropist is trying to spark a new revolution in agriculture. The first Green Revolution improved crop yields, but at the expense of the environment. This time, there may be a chance to get it right.

"Sustainability takes more time, more learning, more people," said John Reganold, Regents Professor of Soil Science at Washington State University. "In the long run it pays huge dividends."

"I really like the fact that here we have this huge philanthropic foundation and they're really trying to help Africa and South Asia," he said. "I don't mind hearing we want to feed people, we want to raise yields, improve their income, get roads and markets in there."

But Reganold said he would like to hear more about how sustainability will be measured and valued. "We tend to go in and say wow, we improved yields," he said. "That's great because these people need to eat. At the same time I'd like to hear wow, we improved the soil so that down the road they're going to be better off."

"They say the right thing, but I'm not sure they're doing the right thing yet," said Hans Herren, a Swiss scientist who won the World Food Prize in 1995. Both Herren and Reganold are attending this year's conference in Des Moines, Iowa.

Gates said in his speech that in their zeal for an ideal environment, some people "have tried to restrict the spread of biotechnology into sub-Saharan Africa without regard to how much hunger and poverty might be reduced by it."

Research into plant genetics is worthwhile, Herren said, but critics of its current usefulness in Africa shouldn't be vilified.

"What I think is wrong is to blame the people who question the utility now as the bad guys responsible for hunger," he said. "Look at the people who have quadrupled yield in perfectly good agriculturally sound systems. Why is this not taken as the example, not to multiply everywhere but as the basis to adapt to different systems?"

Herren took issue with the notion that ecological agriculture is a luxury for rich countries.

"The idea that is deeply ingrained is that the poor can't afford it. That's really a big problem and it's not true. To do it the right way is cheaper because you don't get in debt in the future," he said, by buying more expensive seeds and fertilizers.

More global investment is needed in sustainable agriculture, as well as policies to correct fundamental imbalances in trade and access to resources, he said.