Ammonia Volatilisation from Agricultural Land

Keywords: environment, excreta, farm wastes, fertilisers, grazing animals, N losses.

The processes and mechanisms involved in the production and transfer of ammonia (NH₃) to the atmosphere from agricultural sources and their environmental and agricultural implications are described and discussed. Animal production systems are recognised as the major source of NH₃. This arises from the excretion, as urea, of very large proportions of the N ingested by animals especially under intensive management regimes. Where animals are grazing there are significant, although relatively small, losses throughout the grazing period, i.e. grassland represents a net source for at least half the year. These losses are:

(i) proportional to N input (whether from fertiliser or through N₂ fixation),

(ii) highly variable over both the short and the longer-term, and

(iii) influenced by particular managements e.g. rotational or continuous grazing, and animal species.

Losses of NH₃ resulting from housed animals, i.e. directly from housing, from stored farm wastes and during or after land spreading, provide the major proportion of the NH₃ from animal production. Estimates, based on recent experimental data, are given which indicate the likely contributions of the various sources under UK conditions. Opportunities for reducing losses from grazed swards are few, but a number of methods have been suggested which can be applied to housing and farm waste management which can result in an effective reduction in losses of N as NH₃.

S C Jarvis and B F Pain, AFRC Institute of Grassland and Environmental Research, Hurley, Maidenhead, Berkshire, UK.

35 pages, 8 figures, 9 tables, 105 references.