Nitrogen is one of the primary soil nutrients needed by plants, and in some (particularly agricultural) ecosystems it is a limiting factor for vigorous plant growth. As nitrogen in the form of nitrates or ammonia are deposited on the soil from anthropogenic releases, the excess nitrogen will be taken up by plants until the natural removal rate is reached. Different land use categories (plant types) have different capacities for removing nitrogen. For instance, boreal forests can remove about 15 kg/ha/y whereas arable farm land or rich pasture can remove 40 kg/ha/y or more.
Nitrogen that is not used by plants may be immobilized in the soil by mineralization or other processes that prevent its translocation. Nitrogen that is not used by plants or immobilized in place will contribute to leaching - loss of nitrogen to ground water or surface water .
References
Kuylenstierna, J. C. I., and M. J. Chadwick, 1989: The relative sensitivity of ecosystems in Europe to the indirect effects of acidic depositions. In Kaman, J., D. F. Brakke, A. Jenkins, S. A. Norton, and R. F. Wright, Eds, 1989: Regional Acidification Models. Springer-Verlag. 306 pp.
Tamm, C. O., 1988: Nitrogen in Terrestrial Ecosystems. Question of Productivity, Vegetational Changes and Ecosystem Stability. Department of Ecology and Environmental Research . The Swedish University of Agricultural Sciences. Uppsala.