New Study Confirms Ecological Virtues of Organic Farming

Organic farming has long been touted as an environmentally friendly alternative to conventional agriculture. A new study in the Proceedings of the National Academy of Sciences (PNAS) provides strong evidence to support that claim. Writing in the March 6 online edition of PNAS, Stanford University graduate student Sasha B. Kramer and her colleagues found that fertilizing apple trees with synthetic chemicals produced more adverse environmental effects than feeding them with organic manure or alfalfa.

"The intensification of agricultural production over the past 60 years and the subsequent increase in global nitrogen inputs have resulted in substantial nitrogen pollution and ecological damage," Kramer and her colleagues write. "The primary source of nitrogen pollution comes from nitrogen-based agricultural fertilizers, whose use is forecasted to double or almost triple by 2050."

Nitrogen compounds from fertilizer can enter the atmosphere and contribute to global warming, adds Harold A. Mooney, the Paul S. Achilles Professor of Environmental Biology at Stanford and co-author of the study. "Nitrogen compounds also enter our watersheds and have effects quite distant from the fields in which they are applied, as for example in contaminating water tables and causing biological dead zones at the mouths of major rivers," he says. "This study shows that the use of organic versus chemical fertilizers can play a role in reducing these adverse effects."

The PNAS study was conducted in an established apple orchard on a 4-acre site in the Yakima Valley of central Washington, one of the premiere apple-growing regions in the United States. Some trees used in the experiment had been raised with conventional synthetic fertilizers. Others were grown organically without pesticides, herbicides or artificial fertilization. A third group was raised by a method called integrated farming, which combines organic and conventional agricultural techniques.

"Conventional agriculture has made tremendous improvements in crop yield but at large costs to the environment," the authors write. "In response to environmental concerns, organic agriculture has become an increasingly popular option." During the yearlong experiment, organically grown trees were fed either composted chicken manure or alfalfa meal, while conventionally raised plants were given calcium nitrate, a synthetic fertilizer widely used by commercial apple growers. Trees raised using the integrated system were given a blend of equal parts chicken manure and calcium nitrate.

One goal of the PNAS experiment was to compare how much excess nitrogen leached into the soil using the four fertilizer treatments—one conventional, two organic (manure and alfalfa) and one integrated. When applied to the soil, nitrogen fertilizers release or break down into nitrates—chemical compounds that plants need to build proteins. However, excess nitrates can percolate through the soil and contaminate surface and groundwater supplies.
Besides having detrimental impacts on aquatic life, high nitrate levels in drinking water can cause serious illness in humans, particularly small children. According to the PNAS study, nearly one in 10 domestic wells in the United States sampled between 1993 and 2000 had nitrate concentrations that exceeded the Environmental Protection Agency's drinking water standards.

Washington state produces more than half of the nation's apples. In 2004, the state crop was worth about $ 963 million, with organically grown apples representing between 5 and 10 percent of the total value. But the results of the PNAS study may apply to other high-value crops as well, according to the authors. "This study is an important contribution to the debate surrounding the sustainability of organic agriculture, one of the most contentious topics in agricultural science worldwide," Reganold says. "Our findings not only score another beneficial point for organic agriculture but give credibility to the middle-ground approach of integrated farming, which uses both organic and conventional nitrogen fertilizers and other practices. It is this middle-ground approach that we may see more farmers adopting than even the rapidly growing organic approach."

Adds Mooney, "Organic farming cannot provide for all of our food needs, but it is certainly one important tool for use in our striving for sustainable agricultural systems. We need to explore and utilize all possible agricultural management techniques and technologies to reduce the very large global footprint of the needs to feed a population of over 6 billion people."

Other co-authors of the PNAS study are agroecologist Jerry D. Glover of the Land Institute in Salina, Kan., and Brendan J. M. Bohannan, associate professor of biological sciences at Stanford. The study was funded by the U.S. Department of Agriculture, the National Science Foundation, the Land Institute and the Teresa Heinz Environmental Science and Policy Fellowship Program.

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