Skip to content Skip to navigation

Organic food and your N footprint

What is “Organic”?

In the United States, ‘Organic’ is a United States Department of Agriculture (USDA) certification that ensures that produce and other food ingredients are grown without the use of pesticides, synthetic fertilizers, sewage sludge, genetically modified organisms, or ionizing radiation. Additionally, any animal products (such as meat, poultry, eggs, and dairy) must be produced without the use of antibiotics or growth hormones.

The USDA National Organic Program (NOP) defines organic as follows:

Organic food is produced by farmers who emphasize the use of renewable resources and the conservation of soil and water to enhance environmental quality for future generations. Organic meat, poultry, eggs, and dairy products come from animals that are given no antibiotics or growth hormones. Organic food is produced without using most conventional pesticides; fertilizers made with synthetic ingredients or sewage sludge; bioengineering; or ionizing radiation. Before a product can be labeled "organic," a Government-approved certifier inspects the farm where the food is grown to make sure the farmer is following all the rules necessary to meet USDA organic standards. Companies that handle or process organic food before it gets to your local supermarket or restaurant must be certified, too.

What does Organic have to do with Nitrogen Pollution?

Organic farming practices range in their impact on nitrogen pollution, but many common organic strategies, including crop rotations, composting of plant and animal materials, and use of manure as fertilizer, result in higher rates of N recycling.  Crop rotations prevent nutrient stripping from the soil, and composting plant and animal materials improves N recycling, reducing the introduction of new N pollution to the environment.  The use of organic soil amendments rather than synthetic fertilizers provide crops with molecularly complex N sources that are slow to release N and therefore limit the loss of the N from the field.

While these organic management practices recycle existing reactive N in the environment, organic farms also lose some of this nitrogen to the environment during production. Leguminous cover crops protect soil and reduce nutrient runoff and soil erosion, but they also fix atmospheric nitrogen.  These cover crops are often tilled into the soil as green manure, which adds further nitrogen into the soil.  Moreover, organic practices may result in crop yields that are lower than those of conventional practices, because of lower nitrogen availability and greater pest pressure.

Researchers have found (in preparation for publication) that organic production and conventional production are comparable in terms of nitrogen losses during production, but in terms of newly created reactive nitrogen, organic systems have a smaller impact on the environment. ncreased N availability in organic systems is offset by lower organic yields and high within-system variability, resulting in no significant differences between organic and conventional virtual nitrogen factors.  The difference between systems appears when one looks at the average personal N footprint for new nitrogen contributions, because conventional practices are responsible for a greater amount of new nitrogen being introduced into the system, while organic practices rely on recycling of pre-existing reactive nitrogen.

What is the difference between “new” reactive nitrogen and “recycled” reactive nitrogen?

There are several methods through which reactive N can enter the agricultural system.  “New” N sources describe processes that create reactive nitrogen from previously unreactive atmospheric nitrogen, such as the Haber-Bosch process and N-fixing plants.  “Recycled” N sources, on the other hand, describe the reuse of pre-existing reactive nitrogen, which was already present in the system.  Examples of recycled N sources include compost, manure, and crop residues.

Because organic agriculture relies on these “recycled” N sources, it introduces less new reactive N into the system and thus has a smaller impact on the environment.  Reducing reactive N is critical for decreasing the environmental impacts of N pollution, such as smog, forest die-back, ocean acidification, eutrophication, and climate change.