Ammonia volatilization from field-applied animal slurry—the ALFAM model
Introduction
Ammonia (NH3) volatilization from field-applied animal manure represents a major source of atmospheric pollution and reduces the nitrogen fertilizer value of the manure (Jarvis and Pain, 1990). The environmental impact of atmospheric NH3 forms the background to ongoing international negotiations for reduction of national NH3 emissions (ECETOC, 1994; IPPC, 1996). In addition, legislation controlling nitrogen use in agriculture, both at the EU and national levels, make it increasingly important for farmers to make optimal use of manure nitrogen.
NH3 losses from field-applied manure, particularly slurry, have been measured in many European experiments. The full value of the investment in this research can only be realized if the knowledge gained is communicated effectively to farmers, advisors and legislators. NH3 volatilization from slurries is affected by a wide range of factors, e.g. application techniques, manure composition, crop cover, weather and soil conditions (Sommer and Olesen (1991), Sommer and Olesen (2000); Bussink et al., 1994; Braschkat et al., 1997; Huijsmans et al., 2002).
NH3 volatilization experiments are expensive and are typically designed to examine only one or two of the contributory factors. In contrast, the users of the collected information often need to consider NH3 volatilization under a wide range of weather, soil and agronomic situations, even within a single European region. Alone, the individual experiments conducted by various European research institutes do not provide an adequate basis for this requirement. The ALFAM1 project (Sommer et al., 2001) addressed this problem by combining the data available from these studies into a single database. The data can be used both for developing mechanistic models of NH3 losses from slurry and in the construction of decision support systems.
This paper describes the development and validation of the ALFAM model to predict NH3 loss from field-applied slurry for a range of weather, soil and management conditions. The practical value of the ALFAM model in predicting NH3 losses is also considered and discussed.
Section snippets
Database
The ALFAM database contains data provided by seven European countries (Denmark, Italy, the Netherlands, Norway, Sweden, Switzerland and UK; see www.alfam.dk for a detailed description of the database and the institutes providing data). The choice of data requested from these countries was based on the conceptual model described by Hutchings et al. (1996). Existing knowledge was used to identify the range of factors affecting NH3 volatilization, which included time since manure application, NH3
Results from fitting the model
The results of fitting the model to the measured volatilization data are summarized in Table 2. The table contains sets of A and B parameters relating the explanatory variables to Nmax and Km, respectively (see Appendix A for details). Five parameters with very low statistical significance levels (P>0.4) were fixed at 1 to minimize the variance when using the model to predict NH3 loss for situations (values of the explanatory variables) not covered by the data set used to construct the model.
Conclusion
The ALFAM model development and validation has shown that data from European experiments can be collated in one database and analysed statistically to provide a model with meaningful outputs. The outputs from the modelling are supported by theoretical considerations of impacts of the the weather, soil characteristics and slurry composition on NH3 volatilization from animal slurries applied on fields with short crops (<15 cm) or on fallow land. A Michaelis–Menten-type model provides a good fit
Acknowledgements
The project has been carried out with financial support from the Commission of the European Communities under the work programme “FAIR No. 4057” and by the Danish Ministry of Food, Agriculture and Fisheries under the work programme “Harmony problems and precision agriculture No. HAR98-3”. The project does not necessarily reflect the Commission's views or its future policy in this area.
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