Sustainable Footprint

Nitrogen, problem or solution?

About 2 billion humans, a third of mankind, owe their lives to the discovery of the German chemist Fritz Haber in 1909: he found the way to turn nitrogen gas (which is in its non-reactive form nearly 80% of the atmosphere around us), into ammonia, the basis of synthetic fertilizer. The worlds’ ability to grow food exploded after that. Infertile land could be transformed in fertile fields producing crops year after year. The human population exploded too, starvation was reduced and public health improved. Today still many people do not get enough to eat, but this is not because of not enough is produced, but because of inequality and extreme poverty. It is politics, not lack of food.

A high price
The good news of abundant food for people comes at a high price: the reactive nitrogen made for fertilizer (but it occurs also the result of burning fossil fuels) does not end up in the food we eat. It travels to the atmosphere and the rivers and oceans, where it is a pollutant. Algal blooms, coastal dead zones and ozone pollution are the result. Recent research tells us that also loss of biodiversity and global warming are added to the negative effects, as well as some nasty human diseases.

The growing human population, more people who can afford to eat meat at a regular basis and growing crops for biofuel mean more and more fertilizer-intensive agriculture – and the pollution belonging to that. Still fertilizer must be a leading tool for developing reliable food supply in Africa and other poor regions. This means that we will have to learn to grow more food with less fertilizer.

Too much of a good thing
All life needs nitrogen, but for most organisms the free nitrogen in the air is out of reach. Only a small group of bacteria can break the strong bond between the 2 N-atoms in N2, making them available for chemical fixation, in ammonia and nitrates. These bacteria live in the soil and in water, but most live in symbiosis with certain plants, mainly legumes. Some nitrogen in the air is fixed during lightning and volcanic eruptions too.
Until 100 years ago this was in balance with other bacteria that break down the reactive nitrogen back to free N2. Nowadays humans create more than double the amount of the natural production.
Reactive nitrogen can travel far and cause trouble in many places, even in the most remote corners of our planet.
N-fertilizer added to a field or a garden makes plants grow more. But when it is washed to rivers or the ocean it makes algae grow more. When the algae die and decompose this causes complete depletion of the oxygen in the water, result: everything dies: dead zones. But on land the fertilizer can be harmful too: many (wild) plants cannot cope with too much ‘plant food’, they die and the result is loss of biodiversity.

Because of the air pollution with reactive nitrogen (from agriculture and traffic) the grassland across Europe has lost a quarter or more of their plant species after the deposition of nitrogen was raised by human activities. Reduction of nitrogen deposition is one of the keys of conservation success.

The consequences
Most people do not worry about the loss of rare plant species, but excess nitrogen can also threaten our own health: too much N in drinking water (result of too much fertilizers in the soil) can cause several health problems, including cancer, but probably also Alzheimer’s disease and diabetes. Nitrogen related air pollution affects hundreds of millions of peoples, causing cardiopulmonary problems and driving up mortality rates.

A woman in Thailand, fertilizing her field

Also other diseases, spread by mosquitoes or snails infect more people when nitrogen is abundant – because the food for these agents is more abundant.
Reactive nitrogen in the atmosphere plays an increasing important role in climate change. NO end NO2 play a role in ozone formation. Ozone is harmful for human health, poison for plants and a strong greenhouse gas. And plants growing less can absorb less carbon dioxide.

What to do
We cannot do without using fertilizer for feeding the world. But a more efficient use has to be part of the solution. But too often agriculture has been extremely wasteful causing pollution of air, water and soil, while studies have shown that less fertilizer does not mean fewer crops. The simple fact is that the world is capable of growing more food with less fertilizer by changing the farming practices that have become common in an era of cheap fertilizer and little regard for the long term consequences. In the US people consume only about 10% of what farmers apply to their fields. The rest ends up in the environment.
The doses given are well above the levels needed, typically 20 to 30%. For many of the most common crops in de US a quarter to half of the given fertilizer immediately runs off the field with the rainwater, or goes up in the air.

Precision farming
Precision farming can help: applying the fertilizer (and the water, often a scarce resource as well!) near the plant roots at times of maximum demands. Modern techniques, involving remote sensing of the nutrient levels of the crop help, but this is too costly for poor farmers. But cheaper possibilities are available too: planting winter covers, retaining the nutrients in the soil or planting some cover between the rows, preferably legumes or just applying fertilizer in spring rather than in the fall can make a big difference.

Meat
Much of the nitrogen ends up in crops that go into the mouth of pigs, cows and chickens and a lot of it is expelled as belches, urine and faeces. Reducing meat consumption is useful, but meat remains a useful part of most human diets, so a change in the treatment of animal waste is an important possibility. It can just like human waste be converted to the inert free nitrogen.

Energy
20% of the excess nitrogen comes from energy production. ‘Washing’ the smoke to remove NOx and improving the efficiency will help, as well as forms of renewable energy, except biofuel, which has increased the nitrogen flows, like in the Mississippi river, creating dead zones in the gulf of Mexico. Growing use of biofuel could exacerbate global warming instead of diminishing it.

Solutions
The speed at which nitrogen pollution is rising throughout the world suggests the need for regulation. Implementing environmental standards is essential. At the same time poor countries must be able to raise the use of fertilizer, hopefully avoiding the mistakes made in the US and other rich countries.
Landscape design can make a difference: if there are strips of wetlands between crop fields and bodies of water, the nitrogen inputs in rivers and ocean can be reduced. These wetlands can reduce pollution and provide habitats for migratory birds and other animals.
Finally education and personal choice can make a difference: all of us can reduce our energy and meat consumption. If Americans would switch to a typical Mediterranean diet, meat consumption would be only one sixth and the fertilizer use one half. This could at the same time improve public health: the proteinrich, often unbalanced diets in the wealthier nations link to health problems like heart disiease, diabetes and childhood obesity.

Personal choices
It can help if more people choose to reduce their carbon footprint, by using wind power, eating less meat (and better grass fed beef rather than corn fed) and choosing locally grown food. Personal choices will not solve the problem, but history shows that they can spur societies to move down new paths.
In a way solving the nitrogen problem is more difficult than solving tha carbon problem. We can produce energy without fossil fuels, and this will be done in the future, but we cannot grow food without nitrogen-fertilizers. We will have to learn using it without the drawbacks of reactive nitrogen.

Source: Scientific American, February 2010

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