Carbon dioxide emissions have assumed a role as the key environmental concern in recent years. As this issue dominates headlines and ignites global debate, another pollutant affecting human health and the environment continues to fly under the radar: nitrogen.
Nitrogen is a nutrient essential to human life. One of its gaseous forms, N2, makes up nearly 80% of our atmosphere, and nitrogen fertilizers help feed the world. But it’s also a pollutant agriculture and other industries have spread around the globe, disrupting the nitrogen cycle and affecting human health, air and water quality, and biodiversity.
The serious effects nitrogen pollution is having on the environment are evident, but there's a lack of urgency and collective efforts need to put a stop to the problem, according to Eric Davidson, a senior scientist at Woods Hole Research Center and Soil Science Society of America member.
Davidson recently led a study published by the Ecological Society of America that reviews the major sources of nitrogen in the U.S., the implications of nitrogen pollution, and potential solutions. Davidson hopes this study can help bring people from different industries together to acknowledge this issue and make it an environmental priority.
Although nitrogen emissions from the energy and transportation sectors are declining, agricultural emissions are on the rise. It is believed half of all nitrogen applied during agricultural production is lost to the environment, both as a greenhouse gas and runoff into rivers, lakes, and oceans.
Nitrogen fertilizer consumption in the U.S. is approaching 12 million metric tons of nitrogen per year, and continues to increase. The growing use of nitrogen fertilizer, combined with improved crop varieties and other agronomic factors, has helped increase crop harvests to meet rising food demands.
Davidson says despite these improvements in crop production over the years, large losses of reactive nitrogen to the environment remain a serious problem that must be addressed. “It’s one of the great challenges of our generation. In the future, how are we going to feed 9 billion people in a way that’s sustainable so our children and grandchildren can also feed 9 or 10 billion people?”
The study was supported by a National Science Foundation Research Coordination Network grant, and appeared in the 15th annual Issues in Ecology report, provides potential mitigation options that may help reduce future agricultural nitrogen losses. “The very first Issues in Ecology report was done on the same topic,” says Davidson. “We now know a lot more about the flows of nitrogen and how to quantify them from one sector to another, but many of the same issues talked about in the first report, like climate change, and water and air quality, are still important issues today.”
One option involves better regulating of ammonia emissions from livestock operations in the U.S. The regulation of nitrogen oxide emissions from energy and transportation industries has greatly improved air quality, but agricultural regulations lag behind. “We’ve made a lot of progress in air quality because of the Clean Air Act, but ammonia remains mostly unregulated,” says Davidson.
The study suggests utilizing current technologies and practices can also help reduce nitrogen losses. According to the report, 30 to 50% of nitrogen loss from farm and livestock operations can be reduced using these existing tools, and up to 70 to 90% with innovative applications of existing methods. “Winter cover crops, better timing of fertilizer application, and the more high-tech approaches of precision agriculture are all options,” says Davidson.
Still, cost and outreach remain barriers to the widespread adoption of these methods. Davidson believes scientists will play a crucial role in the future of agricultural nitrogen loss. “The better job scientists can do to demonstrate the tradeoffs and value of these mitigation efforts, the more likely policies will be developed to give farmers incentive to adopt them.”
One of the biggest challenges farmers face is determining optimal nutrient use in the face of unpredictable variations of weather. It’s common for producers to apply extra amounts of nitrogen fertilizer to croplands as an insurance policy. “From a purely economic perspective, that’s a reasonable thing to do,” says Davidson.
He suggests coming up with ways of insuring farmers against unusual losses due to extreme or unusual weather events, which would encourage producers to reduce excess nitrogen application. “It’s a socio-economic sort of issue and it’s important to recognize that farmers have a difficult task of dealing with unpredictable weather.”
In December 2011, the USDA revised its national conservation practice standard on nutrient management. “USDA provides voluntary technical and financial assistance to help producers manage their nutrients to ensure a clean and abundant water supply while maintaining viable farm and ranch operations,” said Agricultural Secretary Tom Vilsack in a statement announcing the revised guidelines.
“Maybe voluntary is the way to go, but there needs to be enough incentive so people will participate,” says Davidson. He also believes funding for agriculture extension agencies is crucial in reaching a larger audience about these problems to then find solutions.
There is no quick fix to the disturbance in the nitrogen cycle. The technology exists to begin reducing agricultural nitrogen pollution, but current policies and the lack of incentives and regulations stand in the way. “It’s time to wake up,” says Davidson. “Humans have altered the nitrogen cycle more than the carbon cycle, and it’s really having an impact on human and environmental health.”
(Photo Courtesy: NASA-Landsat-5, October 9, 2011, showing algae bloom in Lake Erie which scientists blame, in part, on heavy rains leading to run off of an array of pollutants into the lake.)