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Con: Conventional farming produces more with eco-friendly new methods

AMES, Iowa — EDITOR’S NOTE: The writer is addressing the question, Can eating organic help combat global warming?

The public is clearly becoming more interested in lifestyle choices that decrease greenhouse gas emissions. Whether the choice to buy organic food will help that worthy cause, however, is far from a simple question.

Nitrogen fertilizer is a major source of greenhouse gas emissions. Not only is nitrogen fertilizer produced from fossil fuel sources, but its production requires an energy intensive process.

Because of this, organic systems that instead rely on manure and cover crops for nitrogen input typically use less energy. On the other hand, when organic production is compared to low-input conventional farming, research has found similar energy efficiency ratios.

As energy costs rise, more and more conventional farmers are increasing their use of manure fertilizers. Without knowing the input practices of the specific farms that produced the food items, it would be difficult to compare the energy efficiency of organic versus conventional products.

Of course, nitrogen fertilizer is not the only source of energy consumption on farms. The level of mechanization can also impact the energy use.

Organic production, as the name implies, does not use synthetic herbicides. That often means that organic production must keep weeds under control by repeated tillage of the soil. Numerous studies have documented the high-energy inputs of organic carrots and potatoes, for example, because large-scale organic production of those particular crops often relies on mechanical weeding.

Tillage tends to oxidize soil carbon and is thus a major source of carbon dioxide emissions from agricultural landscapes. Reduced reliance on tillage saves energy and preserves soil carbon, and approximately 40 percent of U.S. farms are in no-till production, the vast majority of them conventional.

While reduced tillage is not impossible on organic farms, most still rely heavily on tillage—sometimes as many as four to eight passes over the same ground. Without knowledge of the tillage practices of the specific farm that produced the food item, any consumer would not be able to assess the soil-carbon emissions of an organic versus a conventional product.

The impact of agriculture on soil carbon has other dimensions, as well. Because organic farming uses manures and cover crops as fertilizer, they also tend to return carbon to the soil, and in this way promote soil-carbon sequestration. Several long-term studies have found that organic farming significantly builds soil organic matter compared to non-organic systems.

Other studies, however, have found no significant differences. This is because inputs are not the only governor of soil organic carbon cycling. The influence of climate, soil characteristics and other management impacts are also significant. Without those details, it would be difficult for anyone to know precisely the soil-carbon impacts of the food choices in the produce aisle.

There certainly can be numerous environmental benefits to organic agriculture. Organic farms often promote enhanced on-farm biodiversity, and organic farming lends itself well to more diversified production systems that reduce overall inputs.

Organic labeling, unfortunately, only includes a limited checklist of practices. Many items not on the checklist are enormously influential in the per-food-unit greenhouse gas emissions of a given food product, not to mention the overall environmental impact.

The public is right to be concerned about greenhouse gas emissions, but the variability in agricultural systems makes it very difficult—if not impossible—to generalize about the benefits of organic food choices in this area. Indeed, this issue illustrates the dangers of relying on slogans and simplistic answers to complex environmental questions.

Perhaps the best strategy is to buy local food, which reduces fossil-fuel use and emissions from transportation. Buying local also enables consumers to know their food suppliers and become better educated about the specific production practices associated with what they eat.

Amy Kaleita-Forbes is an assistant professor of agriculture and bio-systems engineering at Iowa State University. Readers may write her at ISU, 205 Davidson, Ames, Iowa 50011-3080, or e-mail her at kaleita@iastate.edu.