Evidence continues to mount supporting the negative impact from excessive nitrogen use in agriculture with results of a new study that indicates sustainable food production is at risk and that the planet's food requirements in 2050 will exceed the ability of farmers to provide an adequate supply to meet demand.
The study, which focused on synthetic nitrogen use efficiency, was conducted by Princeton University's Woodrow Wilson School of Public and International Affairs, and concludes that more efficient use of nitrogen will be required to meet the demands for food by mid-century.
"Nitrogen use efficiency has been proposed by the United Nations as a way to evaluate approaches that decrease nitrogen losses while maintaining or increasing crop yields. Our work reinforces its potential," said Denise Mauzerall, professor of environmental engineering and international affairs at Princeton. "How we feed the planet is going to affect climate, air quality, water quality and biodiversity, so it's critical we do it in a way that is as efficient as possible, or else there will be substantial undesirable environmental consequences."
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Mauzerall is co-author of the study along with Xin Zhang, a postdoctoral research associate at Princeton's Woodrow Wilson School of Public and International Affairs and the Princeton Environmental Institute.
"If we continue the way we've been going, it will lead to an even more significant nitrogen-pollution problem than we have today," Zhang added.
According to researchers, plants use only a portion of nitrogen offered by most commercial fertilizers. The greater part of that synthetic nitrogen is left in the ground, filters into ground or surface water or is distributed into the air. The result is significant emissions of nitrous oxide, a potent greenhouse and ozone depleting gas, and other forms of nitrogen pollution, including eutrophication of lakes and rivers and contamination of drinking water.
Mauzerall says by making nitrogen use more efficient, more of the oxygen would be used by the plant and less would remain to pollute soil, water and air.
During the study, researchers examined how policies and market conditions have influenced farmers' use of nitrogen fertilizers over the past five decades. They studied fertilizer use in parts of the United States, Europe and North Africa, in hopes of better understanding nitrogen efficiency and how it could sustain and improve crop production while minimizing adverse effects on the environment.
According to the study, published recently in Nature, researchers suggest specific nitrogen use targets based on region and crop type be applied to meet 2050 global food-demand projections and environmental stewardship goals announced earlier this year by the United Nations Sustainable Development Goals report. Currently, the global average for nitrogen use efficiency is approximately 0 .4, meaning 40 percent of the total nitrogen added to cropland goes into the harvested crop while 60 percent is lost to the environment. To reduce environmental impacts, the researchers urge an increase in global average nitrogen use efficiency to 70 percent so only 30 percent of the total nitrogen is lost to the environment.
"How we feed the planet is going to affect climate, air quality, water quality and biodiversity, so it's critical we do it in a way that is as efficient as possible, or else there will be substantial undesirable environmental consequences," Mauzerall explained.
In the United States, crop yields have increased over the past two decades without substantial increases in fertilizer use. Mauzerall says this was only possible by adopting technologies that increased nitrogen use efficiency. These improved farming technologies included more strategic irrigation, improved seed sources, slow-release fertilizers and better online planning tools. Likewise, the United States' uptick in producing soybeans, a plant able to produce its own nitrogen, plays a role.
Policies in Western Europe have been more effective at increasing nitrogen use efficiency than in the United States, according the study. For example, the Nitrates Directive, which was implemented in the 1990s, limited farmers' use of manure and the application of fertilizers near water or on slopes to reduce water contamination.
At the other extreme, countries like China and India have gone downhill in terms of nitrogen use efficiency, owing to heavily subsidized fertilizers, which reached $18 billion per year in China in 2010. Because fertilizer is so cheap relative to crop products, farmers tend to use excess quantities to insure higher crop yields.
"China now recognizes the human health consequences of environmental degradation, and they are making impressive efforts to reduce emissions of traditional air pollutants," Mauzerall said.
While ambitious, Mauzerall says the goals highlighted by researchers are attainable, especially if adopted as an indicator for the U.N.'s Sustainable Development Goals.
"This is challenging, but depending on the international commitment for agriculture education and technology transfer, it is much more feasible than it seems," Mauzerall said.