Call for international nitrogen framework

Photo:Mediageek/ BY-NC-SA

A global framework on nutrients could be a way forward to address the extensive problems of pollution caused by excess nitrogen and other nutrients, suggests a recent UNEP report.

Humans have affected nutrient flows on earth ever since man learned to manage fire and was able to turn forests into grasslands, and even more so since the introduction of agriculture, but the scale of the impact has rapidly accelerated since industrialisation, as noted in a global overview of nutrient management, “Our nutrient world”  presented at the United Nations Environment Programme (UNEP) meeting in February in 2013. Professor Mark Sutton, lead author, said: “Our analysis shows that by improving the management of the flow of nutrients we can help protect the environment, climate and human health, while addressing food and energy security concerns.”

Since the development of the Haber-Bosch process in the early 1900s, it has been possible to produce cheap nitrogen fertiliser from atmospheric nitrogen. Between 1950 and 2000, the global use of mineral nitrogen increased from 4 Mt to 83 Mt. This has of course led to increased yields, but not to the same extent as the increased supply of nutrients. The amount of nitrogen in the yield per amount of nitrogen supplied, known as nutrient use efficiency (NUE) has decreased by 60 per cent between 1966 and 2008. 

Although crop yields did not increase as much as the supply of fertiliser, they increased more than the need for food. The crop surplus created scope for substantially increased livestock production. Since the Food and Agriculture Organization began recording statistics in 1960, global meat consumption per capita has doubled. When a crop is converted to meat the overall NUE is reduced, since nitrogen is lost in various stages of production. Considering the full chain of global food production, on average over 80 per cent of the nitrogen is lost to the environment. 

Another aspect of modern livestock production is the concentration in certain regions, to which large quantities of nutrient-rich fodder are imported. This results in extremely high loads of nitrogen and other nutrients in these areas, which further hampers efficient use. 

Co-author Dr Bruna Grizzetti said: “The option of localising agricultural production is a really important one. Crop and livestock farming are often separated by many hundreds of kilometres. Localisation helps improve nutrient recycling, reducing nutrient losses, while bringing the production benefits and pollution responsibilities closer together.”

In addition to the increased supply of nitrogen to agriculture, the formation of nitrogen oxides (NOx) from combustion has also increased the supply of reactive nitrogen to global nutrition flows in the last century. 

The increased flows of nitrogen from agriculture and from combustion have all in all led to an intertwined web of environmental problems such as eutrophication, acidification, stratospheric ozone depletion and the formation of greenhouse gases. So far, the most common policy approach has been to deal with one of the different forms of nitrogen pollution at a time. These include the Convention on Long-range Transboundary Air Pollution (CLRTAP) that deals with emissions of ammonia, the Euro standards for road vehicles that regulate emissions of NOx, the EU’s Nitrate directive that regulates nitrate pollution in water and the UN Framework Convention on Climate Change (FCCC) that deals with emissions of nitrous oxide. 

Today there is no international framework that takes a holistic approach to these highly interlinked problems. The report authors argue that the lack of overview probably leads to an underestimation of the type of action that could have a positive impact on all these problems, while risking so called “pollution swapping”, that is, measures that reduce emissions of a substance, e.g. ammonia, and increase emissions of another, e.g. nitrous oxide. 

One of the key questions is whether it is best to start an entirely new process, or if it is better to expand an already existing one. The authors note that there are already many policy frameworks around and that the best approach is to go for the latter. 

Professor Mark Sutton, said: “One option is to extend and strengthen the mandate of an existing agreement called the ‘Global Programme of Action for the protection of the marine environment from land-based activities’ (GPA). By clubbing together to meet multiple global challenges for food, energy, water and air pollution, climate and health, a much stronger gravity to motivate action can be expected.”

As the name suggests, GPA works primarily with the protection of the marine environment, but within that scope nutrients are one of only three priorities. The prominent role of nutrients in the GPA can be compared to two other possible frameworks, the Convention on Biological Diversity (CBD), which has a much wider focus, and the FCCC, where the main focus is on greenhouse gases. Adding nutrients as a specific target to one of these would be difficult because of competition with other concerns. Another advantage with the GPA, according to the authors, is that it is not a convention with legally binding targets. These can take a long time to negotiate and years will be lost before any real world progress can be seen. The GPA is instead a programme for intergovernmental review that quite soon could develop a consensus around aspirational goals and share best practices. This could result in more rapid progress, they argue.

One aspirational goal that is suggested is to improve countries’ nutrient use efficiency by 20 per cent between 2008 and 2020 – a target that should apply to both crop NUE and full chain NUE (see box for definitions). 

As a long-term target, countries should strive to achieve a NUE for the crop sector of at least 70 per cent and full-chain NUE of at least 50 per cent. There are a few countries in Africa and Asia that already achieve these targets. These are countries where the use of chemical fertilisers is low and the risk of soil depletion and food insecurity is high. In these regions it might instead be necessary to increase the supply of nutrients to match removals from the systems.

The increased NUE, needed in most parts of the world, could be achieved either by making nutrient savings while keeping food and energy production at the current level (constant output scenario), or by increasing production using the same amount of nutrients as today (constant input scenario). 

The constant output scenario would mean reduced costs for fertilisers and the reduction of nitrogen pollution (see figure). A rough cost-benefit analysis of the 2020 target shows savings in the magnitude of US$ 50–400 billion (see table). The constant input scenario would not mean any savings on fertiliser costs, but less nitrogen pollution. The savings that could be made with this scenario are estimated at US$ 15–165 billion without including the value of the increased production of food and energy that it would also lead to.

Kajsa Lindqvist

Our Nutrient World (Febrauary 2013)

Nutrient use efficiency

The concept of nutrient use efficiency (NUE) describes the ratio of nutrient in outputs to the nutrient in inputs. This will vary depending on how system boundaries are set. For crops, NUE boundaries are set at field level, and can be defined as the ratio of nutrients in crop yield and nutrients applied, deposited and bound through biological nitrogen fixation
Full-chain NUE is defined as the ratio of nutrients in final products (e.g., human food consumed) to new nutrient inputs (e.g., Haber-Bosch number, biological N fixation, NOx formation).


Table: Indicative cost-benefit calculation of the global goal to improve nutrient use efficiency (NUE) for nitrogen by 20 per cent.

Figure: Absolute fertiliser savings achived as a result of 20 per cent increased full-chain nitrogen NUE in countries were nitrogen NUE is bellow 50 per cent, if the constant out-put scenario was implemented.

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