For the first 15 years of his academic career, John Ikerd was a self-described traditional agricultural economist: He advised producers that the bottom line — profitability, in other words — was everything.

The overriding goal: To turn a profit no matter what it took.

Today, he's singing a different tune. Now one of the most widely known sustainability advocates in the country, Ikerd touts sustainable farming as the wave of the future.

"We substituted cheap fossil energy for the past 50 or 60 years for the natural productivity of the land," said Ikerd, speaking recently to some 70 people in Freeport, Ill.

Moreover, he now sees rural communities as encompassing more than economics and profitability. First and foremost, rural communities are about people, he stressed.

What's wrong with that argument? Nothing as far as one of Ikerd's fellow economists, Max Runge, is concerned.

Still, Runge says there's a big difference between the qualitative arguments Ikerd and other sustainability proponents advance and the bigger quantitative issue, which ultimately brings us back to the word: Profitability.

"If it's not profitable, it's not going to be sustainable because producers are not going to be willing to do it," Runge says.

That fact was underscored to Runge roughly a year ago while he was preparing a presentation about sustainable farming for a producer's meeting. He was struck not only by the large numbers of ways sustainability is defined but also by how one word — profitability — factored into virtually all of them.

As he sees it, profitability is the axial issue in sustainability.

Therein lies the big dilemma of sustainable farming, he says. Lots of people want a sustainable farming model — a growing number of advocates and policymakers are demanding it — but such a model will not be achievable so long as farmers are unable to earn a living from it, he says.

Granted, Runge is the first to concede that Ikerd's concerns about modern farming's over-reliance on petroleum and water are valid ones. And yes, this over-reliance is likely to become even more acute as farmers struggle to feed a projected 9 billion people by mid-century.

But that doesn't change the basic fact of farming life — profitability. How farmers end up dealing with static supplies of both commodities in the midst of over-population will have to be worked within the larger dynamic of profitability, he says.

As a matter of fact, that dynamic has been operating within farming for a long time, helping define what is sustainable and unsustainable over the long haul.

Indeed, much of what was considered sustainable 30 years ago, isn't sustainable today, says Runge, adding that available supplies of water and energy may prove no exception.

Even so, if there is a transition to a system that uses less energy and water, it will be according to what marketing conditions allow, Runge says.

Yet, as he sees it, this dynamic has worked well in the past and is likely to do so in the future, he says.

"In terms of our overall income, the percentage of what we spend on food has gone down tremendously in the last 80 years," he says. "Some 80 years ago, we were spending slightly less than 20 percent of our income on food, while today that has been reduced to less than 7 percent."

Moreover, the percentage Americans pay for food is considerably lower than other western countries. Germans spend about 11 percent of their income on food, while the French spend more than 15 percent.

For his part, Runge is confident that sustainable practices, such as organic farming, will continue to make steep inroads within U.S. farming and western farming in general within the next few decades.

Several growers in Alabama are already adopting organic practices in varying degrees, and Runge suspects that number will increase as marketing conditions become more favorable.

"There are going to be people willing to grow organic-type foods, but it will only be to the extent that people are willing to pay for it," Runge says.

"The final arbiter will always be the market."