Why organic food isn't as green as you think

To Hindus, cows are sacred. Jewish dietary laws (kashrut) and Muslim dietary laws (halal) prohibit pork consumption. Traditional Catholics abstain from eating meat on Fridays during Lent. Religion and food have forever been intertwined. Food is deep, emotional stuff.

So it's perhaps not surprising that devotees of organic food often embrace with quasi-religious fervor the practice of growing food without synthetic fertilizer or pesticides. [See, for example, my blogpost about Maria Rodale.] But if we want to understand impact of organic agriculture on the planet and on our health, science -- and not faith -- ought to guide us.

New scientific research points to a key drawback of organic agriculture, unfortunately: It is typically less efficient and productive than conventional growing methods. That's a problem for fans of organic because the world has a limited supply of farmland, a billion or so undernourished people, a growing population, an expanding middle class and therefore a vast appetite for affordable and nourishing food.

If, in fact, organic methods are less productive, scaling up the production of organic food at will require more land, contribute to deforestation and cost more than growing our food using conventional methods. That suggests that organic methods alone can't feed the world in a sustainable way.

In a meta-analysis of 66 research studies called "Comparing the yields of organic and conventional agriculture" published last month in Nature, Verena Seufert, Navin Ramankutty and Jonathan A. Foley write:

Overall, organic yields are typically lower than conventional yields.

They go on to say that the yield differences are highly contextual, depending on crops and localities. The studies that they studied, it must be noted, use different methods and many are a decade or two old. This is by no means the last word on this issue. Still, they report that the yield differences

range from 5 percent lower organic yields (rain-fed legumes and perennials on weak acidic to weak-alkaline soils), 13 percent lower yields (when best organic practices are used), to 34 percent lower yields (when the conventional and organic systems are most comparable)

Of course, there are other reasons to embrace organic methods, which may be able to match or even outperform conventional farming methods under certain conditions. Organic methods reduce the use of agricultural chemicals that damage farm workers' health, for example. But, as the authors write, the yield issue should not be ignored:

To establish organic agriculture as an important tool in sustainable food production, the factors limiting organic yields need to be more fully understood, alongside assessments of the many social, environmental and economic benefits of organic farming systems.

Navin Ramankutty

To learn more, I called Navin Ramankutty, a geography professor at McGill University and an author of the study. Much of the debate that goes on about food today focuses on methods rather than outcomes, he told. That was obvious to me after he said it, but I'd never thought about it that way.

Organic farming is a method, or management system; it may well generates less water pollution and fewer greenhouse gases than conventional agriculture, but organic certification doesn't measure those outcomes. Likewise, locavores, a group that includes not just the folks browsing the stands at a farmer's market, but also Walmart, which has promised to buy more locally grown produce, are all about location, and the environmental benefits of localism, if any, are unclear.

One reason why we don't look at outcomes, Navin said, is that "measuring those outcomes is extremely difficulty." Broad generalizations about agriculture don't tend to hold true because, like politics, all farming is local. Florida tomatoes have a different environmental profile from those grown in California.