Nitrogen

Diffuse N losses in agriculture occur mainly by leaching of Nitrate. In general, the magnitude and the variability of the losses depend on

The available amounts of leachable N in the soil profile
The amounts of surplus water for downward transport of N and the predominant pathways of water flow

Illustration: European Commission, Environment DG, 2004.

The spatial and the temporal variability in diffuse N losses may be substantial. This represents a particular challenge in terms of quantification by either field measurements or by modelling, and for the assessments of trends and cause-effect relationships based on measured data.

It is therefore vital for the understanding of the problem of diffuse N losses to have some basic knowledge about N dynamics in agricultural soils and catchments, and the effects of different anthropogenic (e.g. type of crop, fertilisation) and non-anthropogenic factors (e.g. soil texture, precipitation).

The most important natural and man-made sources of diffuse nitrogen losses include:

Organic matter - humus and litter organic N
Manure/faeces - mainly organic N (R-NH2) and NH4+
Fertilisers - nitrate (NO3-), ammonium (NH4+) and urea (CO(NH2)2)
Atmospheric N - mainly dinitrogen gas (N2), with traces of nitrogen dioxide (NO2), nitric oxide gas (NO), nitrous oxide gas (N2O) and ammonia gas (NH3). Atmospheric N may be fixed by plants or bacteria, or it may be deposited on the soil surface by precipitation (in the form of HNO3) or dust.

More information

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Drinking Water Directive

External Links

http://www.physicalgeography.net/fundamentals/9s.html

http://www.neuse.ncsu.edu/nitrogen/biologic.htm