The nitrogen quandary

Nitrogen—the most abundant gas in Earth’s atmosphere—is essential to life on Earth, fueling plant growth and forming proteins, the building blocks of life. In the atmosphere, nitrogen is a stable, nonreactive gas. Only when pulled out of the atmosphere, or “fixed” by natural or human processes does nitrogen become reactive, allowing it to meld into plants and animals, or combine with other elements and escape as reactive gases. Nitrogen naturally moves in and out of the atmosphere, plants, soils, and water, in a system known as the nitrogen cycle.

But Earth’s nitrogen cycle is out of whack. Over the past 100 years, since people figured out how to artificially remove nitrogen from the air and make it into fertilizer, humans have doubled the amount of nitrogen that is naturally pulled out of the atmosphere, with disastrous effects.

One problem is that nitrogen doesn’t discriminate when it comes to helping plants grow. Excess fertilizer leads to algae blooms in rivers, lakes, and the ocean. These blooms thrive by sucking up oxygen from the water, a process called eutrophification that eventually kills other animals and fish that live there.

In addition, nitrogen can escape from soils to the atmosphere in forms that contribute to air pollution and global warming. Gases such as ammonia (NH₃) and nitric oxides (NO_x) contribute to particulate air pollution and ozone that damages human health, while nitrous oxide (N₂O) is a potent greenhouse gas.

“Not a simple problem”

“If we want to do something, we need to find ways to actually limit the release of nitrogen to the environment,” says IIASA researcher Wilfried Winiwarter, an expert on nitrogen emissions mitigation. “This is not a simple problem, because nitrogen is an absolute must in global agriculture,” he says.

In fact, says Winiwarter, many of the easy solutions, for example cutting nitrogen pollution from combustion sources as in power plants or transport, have already been addressed. That leaves agriculture as the major source of nitrogen pollution in many countries. “We don’t usually think of agricultural activities as polluting the environment,” says Winiwarter. “But the average global nitrogen use efficiency is in the order of 30-40%. A lot could be done to improve efficiency by improving nitrogen management in agriculture.”

Winiwarter conducts most of his research using the GAINS model, a global model that simulates emissions of 10 different pollutants and 6 greenhouse gases, based on energy, agriculture, and industry statistics, emission inventories, and data from various countries. The GAINS model can also simulate the potential effects and costs of a range of potential solutions, supporting policymakers and stakeholders to find solutions that can tackle the problem while also saving money.

Researchers feed the GAINS model with detailed data on the activities that lead to pollution. In the case of nitrogen, the GAINS researchers work closely with agriculture and industry experts to ensure that the model accurately represents the real world.

Toward  solutions

In a recent meeting on nitrogen at the Royal Society in London, Mitigation of Air Pollution and Greenhouse Gases Program Leader Markus Amann explained ways in which the GAINS model can help policymakers with realistic projections of how future emissions will unfold, and what people can do to cut those emissions without cutting food production. Amann contributed his insights to a review paper published by the Royal Society this month.

IIASA researchers Winiwarter and Zbigniew Klimont also contributed to a recent United Nations Environment Report (UNEP), which provided a clear list of potential solutions for improving the efficiency of fertilizer use in agriculture, saving money for farmers and reducing pollution. The report was co-organized by the International Nitrogen Initiative (INI), for which Winiwarter heads the European regional center.

Winiwarter notes that while many regions of the world, including China and Europe, are overusing fertilizers, poor countries in Africa are producing less food than would be possible because they don’t have enough fertilizer.  Researchers in other IIASA programs are working on that side of the problem. For example, IIASA Ecosystems Services Management researcher Marijn Van der Velde showed in a recent study that using very small applications of phosphorus and nitrogen could drastically improve crop yields in Africa, while minimizing pollution and cost. 

Reference

Fowler, et. al. 2013. The global nitrogen cycle in the twenty-first century. Philosophical Transactions of the Royal Society B. 5 July 2013 vol. 368 no. 1621 20130164. doi: 10.1098/rstb.2013.0164

M. van der Velde, L. See, L. You, J. Balkovi, S.Fritz, N. Khabarov, M. Obersteiner and S. Wood, 2013. Affordable nutrient solutions for improved food security as evidenced by crop trials.PLoSOne.   http://dx.plos.org/10.1371/journal.pone.0060075

Our Nutrient World: The challenge to produce more food and energy with less pollution. http://initrogen.org/index.php/publications/our-nutrient-world/

Last edited: 07 November 2013