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[1] Information from 846 N 2 O emission measurements in agricultural fields and 99 measurements for NO emissions was used to describe the influence of various factors regulating emissions from mineral soils in models for calculating global N 2 O and NO emissions. Only those factors having a significant influence on N 2 O and NO emissions were included in the models. For N 2 O these were (1) environmental factors (climate, soil organic C content, soil texture, drainage and soil pH); (2) management-related factors (N application rate per fertilizer type, type of crop, with major differences between grass, legumes and other annual crops); and (3) factors related to the measurements (length of measurement period and frequency of measurements). The most important controls on NO emission include the N application rate per fertilizer type, soil organic-C content and soil drainage. Calculated global annual N 2 O-N and NO-N emissions from fertilized agricultural fields amount to 2.8 and 1.6 Mtonne, respectively. The global mean fertilizerinduced emissions for N 2 O and NO amount to 0.9% and 0.7%, respectively, of the N applied. These overall results account for the spatial variability of the main N 2 O and NO emission controls on the landscape scale.

[1] One of the main causes of the low efficiency in nitrogen (N) use by crops is the volatilization of ammonia ( NH 3 ) from fertilizers. Information taken from 1667 NH 3 volatilization measurements documented in 148 research papers was summarized to assess the influence on NH 3 volatilization of crop type, fertilizer type, and rate and mode of application and temperature, as well as soil organic carbon, texture, pH, CEC, measurement technique, and measurement location. The data set was summarized in three ways: (1) by calculating means for each of the factors mentioned, in which findings from each research paper were weighted equally; (2) by calculating weighted median values corrected for unbalanced features of the collected data; and (3) by developing a summary model using linear regression based on weighted median values for NH 3 volatilization and by calculating global NH 3 volatilization losses from fertilizer application using 0.5°resolution data on land use and soils. The calculated median NH 3 loss from global application of synthetic N fertilizers (78 million tons N per year) and animal manure (33 million tons N per year) amount to 14% (10 -19%) and 23% (19 -29%), respectively. In developing countries, because of high temperatures and the widespread use of urea, ammonium sulfate, and ammonium bicarbonate, estimated NH 3 volatilization loss from synthetic fertilizers amounts to 18%, and in industrialized countries it amounts to 7%. The estimated NH 3 loss from animal manure is 21% in industrialized and 26% in developing countries.