Nitrogen is the principal nutrient limiting productivity of agricultural and forest crops. It is also readily lost from soils as a consequence of nitrification, denitrification, and leaching, as well as through biomass removal during harvesting of the crop. In natural ecosystems, nitrogen inputs may be derived from small amounts deposited in rain water and by living organisms, through biological nitrogen fixation. On low nitrogen status soils (such as forest soils following severe fire, or severely disturbed and exposed mineral soils) recolonization by nitrogen-fixing organisms restores fertility over time. In forest and woodland ecosystems, it has been estimated that approximately 40 x 106t of nitrogen are fixed annually by leguminous trees and woody actinotbizal plants (Burns and Hardy 1975).
In intensive agriculture and forestry, demands for increased productivity have been met by the addition of fertilizer nitrogen derived from fossil fuels. As interest in more intensive management of nitrogen fertility in forest ecosystems has increased, so have general concerns over the cost of forest fertilization and the consequences of extensive synthetic fertilizer use on soil and ground water quality. Although immediate benefits from fertilization can sometimes be predicted from agricultural experience and short-term forestry experiments, it may be more appropriate for foresters to determine the long-term management prognosis: Can, or will, the productivity of our forest lands be maintained? How might long-term fertility needs best be met?
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Updated November 14, 2008