Gaseous Losses of Nitrogen Other Than Through Denitrification.

Nitrogen (N) losses from human activities are the major reason behind the growing concerns about the enrichment of the biosphere with reactive N. The single largest cause of human alteration of the global N cycle is crop production. Reactive atmospheric N trace gases resulting from agricultural activities include NO_x (NO and NO₂), NH_x (NH₃ and NH₄⁺), and N₂O. An accurate quantification of sources and sinks for reactive atmospheric N trace gases constitutes a considerable scientific challenge because of large temporal and spatial variability. Major sources of atmospheric NH₃ include volatilization from decomposition of animal excrement, fertilized and unfertilized soils, vegetation, oceans, biomass burning and other combustion processes. Microbial denitrification and nitrification are the main sources of NO_x and N₂O emitted from soils. Chemical denitrification and other kinds of bacterial metabolism involving oxidation or reduction of N also yield trace amounts of these two gases. In addition, NO is released in the burning of fossil fuels used for various agricultural related activities. Burning of biomass for agricultural purposes also results in the formation of NO and NO₂. Effects of N enrichment of the biosphere range from atmospheric changes to alterations of terrestrial and aquatic ecosystems. The fore mentioned information is featured in Chapter 8 of the ASA Monograph entitled “Nitrogen in Agricultural systems”.