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New Study Confirms The 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.
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. (Image courtesy of
Stanford University)Ads by Google Advertise on this site
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.
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. (Image courtesy of
Stanford University)
"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."
Nitrogen treatments
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.
Each tree was fertilized twice, in October and May, and given the same amount of nitrogen at both feedings no matter what the
source--alfalfa, chicken manure, calcium nitrate or the manure/calcium nitrate blend.
Groundwater contamination
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 of 10 domestic wells in the United States sampled between
1993 and 2000 had nitrate concentrations that exceeded the EPA's drinking water standards.
To measure nitrate levels during the experiment, water was collected in resin bags buried about 40 inches below the trees and
then analyzed in the laboratory. The results were dramatic. "We measured nitrate leaching over an entire year and found that it
was 4.4 to 5.6 times higher in the conventional treatment than in the two organic treatments, with the integrated treatment in
between," says John B. Reganold, Regents Professor of Soil Science at Washington State University and co-author of the study.
Nitrogen gas emissions
The research team also compared the amount of nitrogen gas that was released into the atmosphere by the four treatments. Air
samples collected in the orchard after the fall and spring fertilizations revealed that organic and integrated soils emitted larger
quantities of an environmentally benign gas called dinitrogen (N2), than soils treated with conventional synthetic fertilizer. One
explanation for this disparity is that the organic and integrated soils contained active concentrations of denitrifying
bacteria--naturally occurring microbes that convert excess nitrates in the soil into N2 gas. However, denitrifier microbial
communities were much smaller and far less active and efficient in conventionally treated soils.
The research team also measured emissions of nitrous oxide (N2O)--a potent greenhouse gas that's 300 times more effective at
heating the atmosphere than carbon dioxide gas, the leading cause of global warming. The results showed that nitrous oxide
emissions were similar among the four treatments.
"We found that higher gas emissions from organic and integrated soils do not result in increased production of harmful nitrous
oxide but rather enhanced emission of non-detrimental dinitrogen (N2)," Reganold says. "These results demonstrate that organic
and integrated fertilization practices support more active and efficient denitrifier microbial communities, which may shift some of
the potential nitrate leaching losses in the soil into harmless dinitrogen gas losses in the atmosphere."
Sustainable agriculture
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-valued 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 six billion people."
Other co-authors of the PNAS study are agroecologist Jerry D. Glover of The Land Institute in Salina, Ks., and Brendan J. M.
Bohannan, associate professor of biological sciences at Stanford.
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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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