Fixing the world's nitrogen problem

Humanity needs nitrogen to fertilize its grain fields, but the increasing use of the fertilizer worldwide is harmful to the environment and threatens human health. How can a sustainable path be paved for the use of nitrogen?

by Alan R. Townsend and Robert W. Howarth

Billions of people in our world owe their lives to one discovery that happened a century ago. In 1909, the German chemist Fritz Haber from the University of Karlsruhe found a way to utilize the atmospheric nitrogen gas and produce ammonia from it, the active ingredient in artificial fertilizer. Although nitrogen is the most common element in the atmosphere, it is not available to most living things because it does not participate in chemical reactions. Twenty years after Haber's discovery, humanity's ability to grow food improved immeasurably thanks to another German scientist, Karl Busch, who developed a method for implementing Haber's idea on an industrial scale.

In the following decades, the factories turned ton after ton of industrial ammonia into fertilizer, and today many see the invention of Haber and Bosch as one of the greatest contributions to public health in human history. Artificial fertilizers, which were the mainstay of the Green Revolution, allowed farmers to cultivate infertile lands, turn them into productive fields, and grow crops on the same land year after year, without waiting for natural fertilizers to regenerate naturally. Thus in the 20th century the world population jumped from 1.6 to 6 billion people.

But this good news exacted a heavy price from humanity. Most of the active nitrogen we produce - primarily as fertilizer, or to a lesser extent as a byproduct in the burning of the fossil fuels that power our cars and our industrial plants - does not end up in the food we eat. Instead it migrates into the atmosphere, into the rivers and into the oceans, where it transforms its skin from benign to benign pollutant. Scientists have already blamed the active nitrogen for the harmful growth of algae, the formation of dead zones in coastal waters and air pollution with ozone. Recent studies also add to the accusation of contributing to the loss of biological diversity and global warming, and imply that it may increase the rate of some nasty diseases among humans.

Man today produces active nitrogen and injects it into the environment at an increasing rate. Partly because countries vigorously initiate fertilizer-intensive projects, such as the production of biofuels and the production of meat for consumption (a diet rich in meat requires growing a huge amount of grains, which are used to feed the animals). Heavy use of fertilizer to grow grains and uncontrolled burning of fossil fuels are becoming more common in areas such as South America and Asia. It's no surprise, then, that marine dead zones and other nitrogen-related problems, once confined to North America and Europe, are now popping up elsewhere.

However, fertilizers serve as a first-rate tool for developing a reliable food supply system in sub-Saharan Africa and other areas suffering from malnutrition, and that's a good thing. However, the international community must unite and find ways to better manage the use of fertilizers and alleviate their harmful effects in the world. The solutions are not always simple, but neither are they beyond our reach.

The bride is too beautiful

To solve the nitrogen problem, you need to understand the chemistry involved and know exactly how nitrogen creates the environmental problem. The ill effects that nitrogen brings, as well as its good qualities, arise when N2 molecules break down. All living things need nitrogen, but its largest reservoir, 78% of the atmosphere, is beyond the reach of most living things because the gas is chemically inert. Nature's way of providing available nitrogen for life processes is through a small group of bacteria that are able to break the triple chemical bond that holds the two nitrogen atoms together in a process called nitrogen fixation. These specialized bacteria are naturally found on land and in water, both sweet and salty, and also maintain symbiotic relationships within the roots of legumes, some of which are among the most important crops in the world. An additional small amount of gaseous nitrogen is fixed when lightning or volcanic eruptions break it up.

Before humanity began to take advantage of the Haber-Bosch process and other methods for nitrogen fixation, the amounts of active nitrogen created in the world were balanced by another small group of bacteria that turn active nitrogen back into N2 gas in a process called denitrification. But in the lifetime of one human generation this delicate balance was completely violated. Until 2005, humans produced more than 180 million tons of active nitrogen each year, at least twice the amount produced by all natural processes on land per year.

As soon as nitrogen, which some call the prodigal element, is released from its indifferent form, it may cause a host of environmental problems due to its ability to react with many chemicals and spread across the length and breadth of the world. When a new atom of nitrogen enters the atmosphere or a river, it may travel tens to hundreds of kilometers before it stabilizes. Human activity has therefore resulted in an increase in nitrogen rates even in the most remote corners of the earth. But perhaps the most insidious feature of a single active nitrogen atom is its ability to move from one distant environment to another like a criminal on a serial crime spree.

reap the results

A corn field or lawn reacts to the addition of nitrogen in a simple and predictable way: growth increases. But in natural ecological environments the reactions are much more complicated, and sometimes cause concern. When a river full of fertilizer spills into the sea, for example, the water stimulates a proliferation of microscopic plants whose decay consumes the oxygen and leads to the formation of areas known as dead zones. Even on land, not all plants in a complex environment respond to nitrogen addition in the same way, and many of them are unable to cope with a sudden increase in this abundance. The grasslands in most of Europe, for example, lost a quarter of their plant species or more in the decades when man-made active nitrogen reached them from the atmosphere. The problem is extremely widespread and according to a scientific estimate determined not long ago, nitrogen pollution is one of the three most serious threats to biodiversity in the world. The UN's environmental program for the conservation of biological diversity considers the reduction of nitrogen supply an important measure of success in conservation.

The loss of a rare plant does not usually arouse the interest of the public and policy makers. But the excess nitrogen may also threaten our species. A report from the US National Institutes of Health (NIH) suggests that higher than normal levels of nitrates (nitrate ions) in drinking water may cause the development of many health problems, including some types of cancer. Such high levels are often the result of contamination resulting from the high levels of nitrates in conventional fertilizers. Air pollution related to nitrogen which causes the formation of solid particles and the contamination of the lower layers of the air with ozone increases the rate of heart and lung diseases and increases the general mortality rate.

Ecological feedback loops resulting from excess nitrogen (and an excess of another common chemical fertilizer, phosphorus) can cause us many other health problems. The extent of the problem is still unclear, but scientists know that enriching ecosystems with nitrogen changes their ecology in a variety of ways. Recent evidence suggests that excess nitrogen in drinking water may increase the risk of Alzheimer's and diabetes. Excess nitrogen may also increase the release of allergens, such as pollen from certain grasses whose growth is increased by fertilization, into the air. Nitrogen pollution may also encourage the spread of certain infectious diseases. There is evidence that humans are more susceptible to malaria, cholera, bilariasis and West Nile virus when the level of nitrogen in the environment is high.

The spread of these diseases, and of many others, is regulated through the action of other species in the environment, especially those that carry the infectious agent. Mosquitoes, for example, spread the malaria parasite, and snails release the bilarzia worms in the water. The snails demonstrate how nitrogen can trigger a chain reaction: an increased flow of nitrogen or phosphorus increases growth in water bodies, the vegetation serves as food for the snails, and its encouragement accelerates the development of disease-carrying populations. The excess food also greatly accelerates the production of parasites in the snail's body. It is still too early to determine whether the pollution of the environment with an excess of nutrients will generally increase the risk of the spread of diseases, because sometimes the ecological changes caused by the excess of nutrients actually reduce health hazards. But the potential to cause harm creates an urgent need to understand how the change will occur, especially because the use of fertilizers is expected to spread in the coming decades in the disease-ridden equatorial tropics.

Accumulating evidence points the finger of blame towards activated nitrogen when it comes to increasing climate change. The active nitrogen appears in the atmosphere in the compounds nitrogen monoxide (NO) and nitrogen dioxide (NO2), which together are known as NOx. These compounds cause near the surface the creation of one of the most unwanted by-products: ozone. The formation of ozone is disturbing not only because it is harmful to human health but also because on the surface ozone is an important greenhouse gas. Moreover, ozone damages plant tissues and causes damage to crops estimated at billions of dollars per year. The retardation of growth under the effect of ozone impairs the plants' ability to absorb carbon dioxide (CO 2) and reduce global warming.

Active nitrogen threatens the climate in the most alarming way when it appears in the compound nitrogen dioxide (N2O) - the compound of the most powerful greenhouse gases. One N2O molecule increases the greenhouse effect 300 times more than the increase of the greenhouse effect by one CO 2 molecule. Although N2O is much less common in the atmosphere than CO2, it is responsible for the warming of the atmosphere at a rate equivalent to 10% of the CO2 in the atmosphere. But it is important to add that sometimes excess nitrogen can reduce warming, for example when it combines with other gases and creates aerosol particles that return the radiation reaching the earth, and when it encourages the growth of forests in low-nitrogen areas that absorb more CO2 from the atmosphere. But although the balance between nitrogen's warming and cooling effects is still unclear, there are increasing signs that the continued artificial production of excess nitrogen by humans will accelerate climate warming.

What to do?

Approximately two-thirds of the nitrogen that harms the earth today is fixed by man in fertilizer production processes, and even so, stopping production is out of the question. The fertilizer is too important to feed the world. But ensuring efficient use in the rich and developing countries must be part of the solution.

The rich countries have paved the way for an agricultural system that often overuses the use of nitrogen and does not pay attention to the efficient use of this important resource. Too often the use of nitrogen resembles a hasty investment spree where poor returns are achieved and the true costs are ignored. Whereas in other parts of the world more than a billion people are trapped in cycles of poverty and malnutrition. The best example of this is perhaps sub-Saharan Africa. Sometimes the agricultural production in these areas fails to meet even the most basic nutritional requirements, and certainly does not provide a source of income. There is no doubt that nitrogen fertilizer will improve the living conditions of the people there. Adopting a new policy to supply affordable fertilizer and a greater variety of seeds to poor farmers in Malawi, for example, resulted in a significant increase in yields and reduced hunger.

But these fertilizers should not be spread recklessly. The evidence is here: Studies from the corn belt of the US Midwest to the wheat fields of Mexico have shown that over-fertilization was a common practice in the world's grain basins, and that reduced fertilization often did not reduce yields. The simple facts are that overall the world is able to grow more food with less fertilizer by changing the farming habits that have become common in an era of cheap and widespread fertilizer and inattention to the long-term effects of its use. A great start would be to simply reduce the amount of fertilizer given to many crops. Many times the dose of fertilizer is much higher than what is needed to guarantee a peak yield, and this leads to excessive loss of it and its reaching the environment. In the United States, people consume produce that comes from only slightly more than 10% of the fertilizer that farmers spread on the fields each year. Sooner or later, the residue ends up in the environment. Despite the various estimates, in most conventional crops a quarter to a half of the fertilizer is immediately washed off the fields by the rain or finds its way into the atmosphere. Precision agricultural technologies can also help. Spreading fertilizer near the roots only at the time of maximum demand is one example of methods already used in some rich agricultural regions of the world. The use of GPS systems to map the fields in combination with assessments based on remote sensing of the amounts of nutrients in the soil allows farmers to improve their calculations with regard to the dates of grain fertilization and the amount of fertilizer needed. But this sophisticated equipment is expensive and beyond the reach of many independent farmers, so precision agriculture is not a panacea.

But not all solutions involve advanced technology. A cheap and effective method is, for example, planting winter crops (in cold countries) that cover the soil and preserve the nitrogen instead of leaving the soil exposed for months. Another method is the cultivation of appropriate vegetation between the rows of more profitable crops, such as corn. To make a big change sometimes it is enough to simply fertilize the field right before spring sowing in the northern countries, and not months earlier in the fall.

The world can also benefit from changes in meat production processes. Most of the nitrogen that reaches crops ends up in the mouths of pigs, cows, and chickens, and most of that nitrogen is excreted in bloat, urine, and feces. There is no doubt that reducing meat consumption in the world will be a welcome step, but meat proteins will remain an important component of the human diet. Meat production must therefore become more efficient. A change in the diet of the animals, for example feeding the cattle more grass and less corn, could be of little help, as well as better treatment of waste in a manner similar to the purification of human sewage, which will convert active nitrogen back into indifferent atmospheric nitrogen [see "Hamburger Greenhouse" by Nathan Piala, Scientific American Israel, June -July 2009].

The energy industry, which releases about 20% of the world's excess nitrogen, can reduce the amount of active nitrogen released by burning fossil fuels through better deployment of technologies to remove NOx from chimneys and other sources of industrial pollution. In addition, an ongoing worldwide effort to improve energy efficiency and switch to cleaner, renewable energy sources will reduce nitrogen and carbon emissions. Removing the old and most inefficient power plants from the production line, tightening the emission standards for vehicles and facilities, reducing electricity production using traditional fuel burning methods and switching to fuel cells can bring about a significant change.

And of course, one of the sources of renewable energy, biofuel produced from corn, increases again the demand for fertilizer. The incredible increase in corn ethanol production in the United States, nearly quadrupling since 2000, has already visibly increased the flow of nitrogen down the Mississippi River, which carries excess fertilizer to the Gulf of Mexico, where the fertilizer encourages algae blooms and creates dead zones. A report by the Scientific Committee for Environmental Problems (written when it belonged to the International Science Council) stated in April 2009 that continuing to take the "business as usual" approach regarding biofuel production could worsen global warming, threaten food security and trigger respiratory diseases among humans, in addition to The known ecological problems.

How to repair the damage?

Human society already has technical tools to manage nitrogen more efficiently while maintaining many of its benefits and significantly reducing the risk arising from it. As for the challenges in the field of energy, transitioning to a sustainable use of nitrogen will not be simple, nor are there any miracle solutions. Moreover, technological know-how is not enough: without economic incentives and other policy changes, nothing will be able to solve the problem.

The increasing rate of nitrogen pollution around the world implies the need for orderly control practices. There is probably a necessity to enforce or tighten the environmental standards, such as setting a daily cap on the amount of nitrogen that is allowed to be injected into flowing water and setting the concentrations of active nitrogen that are allowed in emissions from burning mineral fuel. In the United States and other countries, steps are being taken to implement regulatory policies, both at the national and regional levels, and they are having a certain degree of success [see "Reviving Dead Areas" by Lawrence Mee, Scientific American Israel, April-May 2007]. Following the necessary changes made in global policy, today the fertilizer also reaches areas that the green revolution overlooked. In these areas, it is therefore necessary to implement sustainable methods from the very beginning, in order to avoid repeating the mistakes made in the United States and elsewhere.

But it is not necessary to threaten with a financial fine for emissions that exceed the standard in order to bring about promising improvements in the utilization of nitrogen. It is also possible to use tools based on the free market, such as quotas passing to the trader. This approach was very successful in the treatment of sulfur dioxide emissions from factories. Steps are now being taken to adopt similar approaches to dealing with NOx pollution, including the US Environmental Protection Agency's NOx allowance trading program, which began operating in 2003. This policy can also be extended to fertilizer effluents and emissions from the livestock sector, although monitoring animal bloat is more difficult than monitoring emissions from coal-fired power plant stacks.

Other approaches to solving the problem are also beginning to have an effect, such as better planning of the use of the route of the agricultural areas, and especially making sure that grain fields close to bodies of water are surrounded by swampy buffer zones that greatly reduce the entry of nitrogen into the flowing water and coastal waters. Conservation of coastal areas, as promoted by the United States conservation plan, could perform a dual role: not only to reduce nitrogen pollution but also to serve as a necessary habitat for migratory birds and a wide variety of other species.

In order to achieve considerable progress, it will be necessary to rethink the financial support for farmers as well. Subsidies that reward environmental protection may be particularly effective for quickly changing work habits. A non-profit experiment conducted by the American Farm Fund showed promising signs. The farmers who participated in the experiment agreed to reduce the use of fertilizer and to direct part of the money they saved from not purchasing it to a common fund. They fertilized most of their crop at a reduced rate, and only small experimental plots were fertilized with a lot of fertilizer. If the plots trampled with excess fertilizer achieve higher yields than the average of the entire field, the joint fund pays the difference.

As one of us (Howarth) reported in the 2005 Millennium Ecosystem Assessment report, such payments would be rare given the current tendency to over-fertilize many crops. In the grain basins of the North Midwest of the United States (the main source of nitrogen pollution of the Gulf of Mexico, which leads to the formation of dead zones) the farmer usually uses 20% to 30% more fertilizer than the amount recommended by agricultural guides. The crops of the farmers who participated in the mentioned experiment to reduce the use of fertilizer and experiments similar to it did not decrease, as expected, and the joint coffers swelled without receiving a penny from the taxpayers. And since the amount the farmers paid to the joint fund was less than the amount they saved from not buying fertilizer, they made a profit.

And finally, improving public information and personal choice can play a decisive role. And just as many have begun to reduce their energy consumption, so people from all walks of life can choose a less wasteful lifestyle when it comes to nitrogen.

An important improvement would occur if Americans ate less meat. If Americans were to switch to a typical Mediterranean diet, where meat consumption is about one-sixth of the meat consumption in the United States, not only would their health improve, but the use of fertilizers in the country would be cut in half. Such a dietary and agricultural change could result, at the same time, in reducing nitrogen pollution of the environment and improving public health. Nitrogen-rich agriculture in the rich countries leads to excessive protein consumption and often to an unbalanced diet that causes health problems, from heart disease and diabetes to childhood obesity.

A personal choice aimed at reducing the personal carbon footprint may help not only on the industrial level, where this is reflected, among other things, in supporting wind energy or hybrid cars, but also on the agricultural level. Eating less meat and preferring food that grew close to home and meat from animals that ate grass and not corn deal with the carbon and nitrogen problems together. Personal choice alone cannot solve the problems, but history shows that it can spur entire societies to move onto a different path. The well-known balance between the climate and energy production, which for many years was considered nothing more than a hypothesis, appears today everywhere, from the president's speeches to billboards and regulation plans.

The nitrogen problem is, unfortunately, more difficult than the carbon problem in one important respect. As far as the carbon problem is concerned, it is reasonable to aspire to a future where we can produce energy without mineral fuels that emit CO 2. But it is impossible to imagine a world that does not have to produce significant amounts of active nitrogen. Artificial fertilizers have been, and will continue to be, essential to feeding the world. But if we continue on the path of "business as usual", and continue to increase the nitrogen industry, the disadvantages of the Havre discovery will more and more overshadow its enormous advantages.

However, as we argued here, it is possible to significantly reduce the problems of the nitrogen cycle using existing technologies and at a reasonable price. We can, and must, do better. This will require an immediate and continuous effort, but it is certainly possible to reach a sustainable future for the nitrogen economy.