The Why Files The Why Files --

21 JUL 2005

Organic agriculture: Testing time
A long-term study of organic farming shows that corn and soybean yields could rival those of conventional farming, while offering major benefits in soil fertility, drought resistance, and water pollution. Many people accept that growing crops without synthetic fertilizers, pesticides or herbicides can bring environmental benefits. But can organic put as much food on the table? Does it require too much weed-whacking labor? Is it profitable?

Answering these questions is key to the continuing growth of one of the hottest sectors of American agriculture.

Ironically, all agriculture was organic agriculture until the 20th century, when agricultural scientists and agribusinesses discovered synthetic fertilizers and pesticides.

Now, organic is making a comeback. Faced with consumer worries about questionable chemicals in food, and an undercurrent of concern about the environment, the old is becoming new.

Two tractors pull machines that uproot beets and chop off tops.
Harvesting organic beets at Angelic Organics. © David Tenenbaum

In 2005, certified organic farms grossed more than $25 billion worldwide, according to In the United States, organic corn production, much of it sold to farmers raising organic meat, is growing 20 percent a year.

The new study, published in BioScience, and written by a group headed by David Pimentel, a Cornell University professor of ecology and agriculture, reports on 22 years of results from the Farming Systems Trial at the Rodale Institute. Rodale researches and promotes organic agriculture.

The trial compared corn and soybeans grown with three methods:

The researchers recorded the mass of crops, cover crops and weeds; leaching of nitrates and herbicide; carbon, nitrogen and water in the soil; and rain, energy inputs and economic returns.

Soybean yields per hectare were 2,461 kilograms for organic crops with animal manure, 2,235 kilograms for organic with nitrogen from legumes, and 2,546 kilograms for conventional soybeans. (In American units, that's 36.5, 33.1 and 37.8 bushels per acre.)

The organic-legume technique was changed in 1991 to a five-year rotation with corn, soybeans, wheat, and red clover-alfalfa hay. The complicated crop sequence aimed to reduce soil erosion, control weeds and insects, and supply nitrogen to the crop.

Using that five-year rotation, corn yields were similar: 6,431 kilograms per hectare for organic-manure, 6,368 for organic-legumes, and 6,553 for conventional. (That's 102, 101 and 104 bushels per acre.) The conventional yield, we notice, lines up nicely with Pennsylvania statewide averages for the same period.

Even though the year-to-year comparisons were equal, the total corn yield over a series of years would be lower for the corn-legume system, which devoted considerable growing time to the nitrogen-producing legumes.

All in the carbon

Still, organic corn excelled in drought years, with yields 28 to 34 percent above conventional. Drought resistance can make you money, Pimentel says, because prices rise when overall yield is tight. If you manage a good crop in a dry year, each bushel fetches more.

Drought resistance stems from the soil's high organic content, Pimentel adds. Soil in an organic-agriculture field contains more humus, and this decaying material holds water for the dry years.

Humus reduces erosion by giving structure to the soil. Cover crops, another key part of the organic rotation, reduce erosion by protecting soil from rainfall. Although the researchers did not measure erosion, Pimentel notes that "in the organic system, cover crops were used constantly, so the soil was generally protected, almost 365 days a year."

Production was higher than use from 1996 to 1999.
World grain usage exceeded production in 2000. We've been drawing down our supplies ever since. Courtesy of the Food and Agriculture Organization

Soil degradation is a global problem, says Pimentel. "Worldwide, we are abandoning 10 million hectares per year due to erosion, and we lose another 10 million hectares to salinization," the accumulation of salt on irrigated land. Meanwhile, the United Nations says 850 million people go to bed hungry.

Bottom line
In the Rodale test, conventional crops had higher costs for fertilizer, lime (to reduce soil acidity), herbicide and pesticide. Organic crops faced higher costs for seed, machinery and labor. Organic required 35 percent more labor, which reduced net return to $127 per hectare, compared to $162 per hectare for conventional. To earn the same profit, the researchers calculated that organic grain would have to fetch a 10 percent premium in the market; the actual premium is at least 65 percent, according to New Farm Organization, a Rodale affiliate.

Organic corn uses 30 percent less energy than conventional, soybeans are about the same.
The Rodale Institute compared two methods for growing organic corn and soybeans to the conventional approach. Conventional corn uses a lot of fertilizer, which comes from fossil fuel. Soybeans gather their own nitrogen. Courtesy Pimentel et al.

The prospects for organic grain could get better if fossil-fuel prices continue their rise, since so much nitrogen fertilizer comes from natural gas. The price of nitrogen fertilizer, Pimentel notes, "is increasing rapidly, right along with jet fuel and gasoline prices." With cover crops or manure, he says, "You can raise corn with 30 percent less energy... you get the nitrogen free."

-- David Tenenbaum

- Environmental, Energetic, and Economic Comparisons of Organic and Conventional Farming Systems, Pimentel, David; Hepperly, Paul; Hanson, James; Douds, David; Seidel, Rita, BioScience, July 2005, vol. 55, no. 7, pp. 573-582(10).

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Manure Menace
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