Ammonia volatilization from field-applied animal slurry—the ALFAM model

A statistical analysis of European ammonia (NH3) volatilization data (from Denmark, Italy, the Netherlands, Norway, Sweden, Switzerland and UK) collated in a database produced a model that is supported by theoretical considerations of the effect of explanatory variables (see www.alfam.dk). Volatilization could be described mathematically by a Michaelis–Menten-type equation, with the loss rates as the response variable (R2=80%). Variables significantly affecting NH3 volatilization throughout Europe are soil water content, air temperature, wind speed, slurry type, dry matter content of slurry, total ammoniacal nitrogen content of slurry (TAN=NH3+NH4+), application method and rate, slurry incorporation and measuring technique. The model was used to estimate the NH3 volatilization from typical cattle and pig slurries applied in Italy, England, Norway and Denmark. Climate observations from the following three periods in year 2000 were used as input: (1) 1 week before the normal sowing time for spring crops, (2) mid-season, and (3) 1 week after harvesting. There was little difference in the total NH3 volatilization from slurry applied in the three periods, principally due to interactions between soil water content and air temperature. The time from application to when 10% of the applied TAN was lost was similar for countries in the south and north of Europe, primarily due to the low wind speeds counteracting the effect of higher air temperatures at the southern location. To reduce NH3 volatilization, the slurry should be incorporated faster in mid- and late-season than in the early spring, due to increasing air temperatures during the growing season.