[1] Information from 846 N 2 O emission measurements in agricultural fields and 99 measurements for NO emissions was summarized to assess the influence of various factors regulating emissions from mineral soils. The data indicate that there is a strong increase of both N 2 O and NO emissions accompanying N application rates, and soils with high organic-C content show higher emissions than less fertile soils. A fine soil texture, restricted drainage, and neutral to slightly acidic conditions favor N 2 O emission, while (though not significant) a good soil drainage, coarse texture, and neutral soil reaction favor NO emission. Fertilizer type and crop type are important factors for N 2 O but not for NO, while the fertilizer application mode has a significant influence on NO only. Regarding the measurements, longer measurement periods yield more of the fertilization effect on N 2 O and NO emissions, and intensive measurements (!1 per day) yield lower emissions than less intensive measurements (2-3 per week). The available data can be used to develop simple models based on the major regulating factors which describe the spatial variability of emissions of N 2 O and NO with less uncertainty than emission factor approaches based on country N inputs, as currently used in national emission inventories.

[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.

A model for P sorption is described which is based on previous studies concerning the interaction of phosphate with gibbsite and with a sandy soil. Formation of coatings of metal phosphate on metal oxide particles constitutes the presumed mechanism of the sorption process. Diffusion of phosphate ions through the surface coating is taken as the rate‐limiting step. The relating diffusion equation is first solved with the condition of constant concentration for reactive particles of well defined geometry. Then it is shown that for any assembly of reactive particles the sorption as a function of the concentration‐time product should yield one curve, irrespective of the reaction pathway. The form of this curve can only be predicted for very specific cases. The above curve, however, can be determined experimentally, allowing the calculation of the phosphate sorption rate for any combination of concentration and sorption values. This is very useful in modeling the transport of P through soil systems. Experimental evidence is given which supports the model theory.

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