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Nitrogen pollution: Forgotten element of climate change

It has hidden behind carbon emissions in headlines for some time, but it is arguably a more challenging problem

As the world’s population heads towards nine billion, we need to grow more food while minimising the problems associated with nitrogen fertiliser use.

In Europe alone, the environmental and human health costs of nitrogen pollution are estimated to be between €70 and €320 billion ($A100 and $A450 billion) per year.

Nitrogen emissions like ammonia, nitrogen oxide and nitrous oxides contribute to the formation of particulate matter and acid rain. These cause respiratory problems and cancers for people and damage to forests and buildings.

A gargoyle damaged by acid rain. Picture: Nino Barbieri via Wikimedia Commons
A gargoyle damaged by acid rain. Picture: Nino Barbieri via Wikimedia Commons

Nitrogenous gases also play an important role in the planet’s atmospheric climate regulation. Nitrous oxide is a particularly potent greenhouse gas as it is over 300 times more effective at trapping heat in the atmosphere than carbon dioxide.

Nitrogen from fertiliser, effluents from livestock, and human sewage boost the growth of algae and cause water pollution. The estimated $8.2 billion damage bill to the Great Barrier Reef is a reminder that our choices on land have big impacts on land, water and the air downstream.

Lost nitrogen harms farmers too, as it represents reduced potential crop growth or wasted fertiliser. This impact is most acute on smallholder farmers in developing countries, for whom nitrogen fertiliser is often the biggest cost of farming. The reduced production from the lost nitrogen can represent as much as 25 per cent of the household income.

The solution to the nitrogen challenge will need to come from a combination of technological innovation, policy and consumer action.

Nitrogen: the essential ingredient in every recipe

Nitrogen is an essential building block for amino acids, proteins and DNA. Plant growth depends on it; animals and people get it from eating plants or other animals.

Nitrogen gas (N2) makes up 78 per cent of the air, but it cannot be used by plants. Nitrogen fertilisers are usually made from ammonia, a form of nitrogen which the plants prefer.

A century after the development of the Haber-Bosch process gave us a way to manufacture nitrogen fertiliser, our demand for it has yet to level off.

The use of nitrogen fertiliser has risen from 11 million tonnes in 1961 to 108 million tonnes of in 2014. As carbon dioxide levels continue to rise in the atmosphere, plants will also likely demand more nitrogen.

In fact, nitrogen from fertiliser now accounts for more than half the protein in the human diet.

Yet some 50 per cent of applied nitrogen is lost to the environment in water run-off from fields, animal waste and gas emissions from soil microbe metabolism. These losses have been increasing over the decades as nitrogen fertiliser use increases. Reactive nitrogen causes wide ranging damage, and will cause more damage if nitrogen losses are not reigned in.

Faced with a growing population and changing climate, we need to optimise the use of nitrogen and minimise the losses more than ever.

From farm to fork

One way to understand our nitrogen use is to look at our nitrogen footprint – the amount of nitrogen pollution released to the environment from food, housing, transportation and goods and services.

Research by University of Melbourne PhD candidate Emma Liang has shown Australia has a large nitrogen footprint. At 47 kg of nitrogen per person each year, Australia is far ahead of the US, which came in with 28 kg of nitrogen per person each year.

A high animal-protein diet appears to be driving Australia’s high nitrogen footprint. The consumption of animal products accounts for 82 per cent of the Australian food nitrogen footprint. Animal products carry high nitrogen costs compared to vegetable products. Both products start with the same cost in nitrogen as a result of growing a crop, but significant further losses occur as the animal consumes food throughout its life cycle.

Choosing seafood over beef or lamb can reduce your nitrogen footprint. Picture: Public domain
Choosing seafood over beef or lamb can reduce your nitrogen footprint. Picture: Public domain

The N-Footprint project aims to help individuals and institutions calculate their nitrogen footprint. It shows how we can each have an impact on nitrogen pollution through our everyday choices.

We can choose to eat lower nitrogen footprint protein diets, such as vegetables, chicken and seafood instead of beef and lamb. We can choose to reduce food waste by buying smaller quantities (and more frequently if necessary), and composting food waste. The good news is that if we reduce our nitrogen footprint, we also reduce our carbon footprint.

Back to the farm

In the meantime, efforts to improve nitrogen use efficiency at the production level must continue. We are getting better at understanding nitrogen losses from soil through micrometeorological techniques.

Where once they sat in the sun with plastic bucket chambers, glass vials and syringes, scientists now use tall towers and lasers to detect small changes in gas concentrations over large areas and send the results directly to our computers.

We now know nitrification (when ammonia is converted to nitrate) is an important contributor to nitrogen losses and therefore climate change and damage to ecosystems. It is a process researchers – and farmers – are targeting to reduce nitrogen losses.

Nitrification inhibitors are chemical compounds now used commercially to keep nitrogen in the ammonium form, which plants prefer, and to prevent the accumulation of nitrate, which is more easily lost to the environment.

As this technology advances, we are starting to address the question of how these inhibitors affect the microbial communities that maintain the health of our soil and form the foundation of ecosystems.

For example, our research shows that 3,4-dimethylpyrazole phosphate (better known as DMPP) inhibits nitrification without affecting soil microbial community diversity.

There is some excitement coming from observations that the root systems of some tropical grasses also inhibit nitrification. This opens up a management option to slow nitrification rates in the environment using genetic approaches.

Solving the challenge of nitrogen use will require research into more efficient ways for primary producers to use nitrogen, but it will also need government leadership and consumer choices to waste less or eat more plant protein.

These tools will make the case for change clearer, and the task of feeding the world greener.

On 4-8 December, leading international researchers are meeting in Melbourne for the 7th International Nitrogen Initiative Conference to discuss the best new solutions to problems in nitrogen use. For a more in-depth look at these issues, visit the INI2016 website or join a range of food and production experts at the Good Food for 9 Billion: Community Forum on Wednesday 7 December.

Banner Image: Nicholas A. Tonelli via Wikimedia Commons.

This article has been co-published with The Conversation.

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