Long Term Global and Regional Trends in the Nitrogen Cycle

Globally, nitrogen is found in the terrestrial ecosystem as dead organic matter (89.5%), with live biomass accounting for 4% and inorganic nitrogen 6.5% of this

Table 1 Nitrogen production (109 kg Nyr 1)

Nitrogen production (id9 kg Nyr 1)



Anthropogenic sources



Terrestrial ecosystem



Marine ecosystems



Fixation by lightning






source. Natural sources of nitrogen have seen a small decline since 1890 (Table 1). Losses of biomass due to large-scale burning and forest clearances during the late twentieth century have contributed to the decline of this reservoir.

Natural reservoirs now cannot provide nitrogen in the quantity required for global food production. In 1890, total anthropogenic N production was approximately 15 x 109kgNyr~\ but by 1990 this had risen by an order of magnitude to approximately 140 x 10 kgNyr~ .

In the terrestrial ecosystem, globally, nitrogen production is generally driven by the use of fertilizers for intensive agriculture, with cultivation and combustion contributing approximately 38% to all anthropogenic sources. However, this is not evenly distributed across the world regions. Asia produces almost half the world's nitrogen fertilizers, followed by Europe then North America (Table 2). Africa, Latin America, and Oceania combined contribute less than 12% of global nitrogen production.

Significant changes to the nitrogen cycle have been apparent since the 1960s. This is closely linked to expanding human populations and an increasing demand for food and energy. Creation of anthropogenic nitrogen in Asia increased from -14.4 x 109kgNyr_1 in 1961 to -68 x 109 kgNyr-1 by 2000, and is set to increase to

Table 2 Global anthropogenic nitrogen production 1990 (x109 kg Nyr 1)

World region Fertilizer production Cultivation Combustion Total

Europe and Former Soviet Union 21.6 3.9 6.6 32.1

North America 18.3 6.0 7.4 31.7

Table 3 European N Budget 1990

Ninput X109 kgNyr 1 N output x109kgNyr1

N-fertilizer production 14.0 Denitrification 13.8

Combustion and industry 3.3 Emissions of NH3 and NOx 7.8

Biological N fixation 2.2 Sewage and industry 2.6

Deposition 7.3 Riverine flux to oceans 4.0

Imported products 7.6 Exported products 6.3

Total 34.5 Total 34.5

105 x 109 kgNyr 1 by 2030. North America doubled its N production between 1961 and 1997, with most of the increase occurring during the 1960s and 1970s. Although the largest increase was in use of inorganic N fertilizer, emissions of NOx from fossil fuel combustion also increased substantially. By 1997, even though N fixation had increased, fertilizer use and NOx emissions had increased more rapidly and two-thirds ofreactive N inputs were denitrified or stored in soils and biota, while one-third was exported, the largest export being in riverine flux to coastal oceans, followed by export in food and feeds, and atmospheric advection to the oceans. The consumption of meat protein is a major driver behind N use in agriculture in North America. Without changes in diet or agricultural practices, fertilizer use will increase over the next 30 years, and fluxes to coastal oceans may increase by another 30%.

Similar trends are mirrored in the European N budget (Table 3). By 1990, N inputs are approximately 34.5 x 109 kgNyr-1. The major process of N fixation being fertilizer production at -14.0 x 109kgNyr-1, with industry and combustion accounting for a further -3.3 x 109 kgNyr-1. Imported N from products such as animals, animal feeds, food, fertilizers, forestry products, exceeds the amount of N exported outside Europe. Furthermore, exports in riverine flux to oceans accounts for -4.0 x 109 kgNyr-1.

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