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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.
Bouwman et al. (Sat,) studied this question.