Managing Ammonia Emissions Cost Effectively

Critical levels of acidification and nutrient-N deposition are still exceeded in many parts of Europe. Even with further reductions in emissions of NO_x , significant exceedance of critical loads and levels will continue due to NH₃ deposition. Hence, a requirement to reduce NH₃ emissions has been included in a multi-pollutant, multi-effects protocol to reduce acidification and eutrophication in Europe, agreed by the UNECE Convention on Long-Range Transboundary Air Pollution. Agriculture is recognised as the source of c. 80-90% of European NH₃ emissions, with c. 70-80% of the total emitted during livestock production.

Emissions of NH₃ take place at all stages of manure management: from buildings; during storage; following application of manures to land and during grazing. Measures to reduce NH₃ emissions at the various stages of manure management are interdependent, and combinations of measures are not simply additive when combining their emission reduction. Reducing NH₃ emissions following application of manures to land is particularly important, as these are a large component of NH₃ emissions and land application is the last stage of manure management. Without abatement at this stage much of the benefit of reducing emissions from buildings and stores may be lost. In order to estimate the cumulative effects of a series of abatement measures, a mass-flow approach is needed. The source of NH₃ emission from livestock excreta and manure is regarded as a pool of total ammoniacal-N (TAN) which is not significantly added to during manure management. At each stage of manure management, a proportion of TAN may be lost, mainly as NH₃, and the remainder passed to the next stage. This approach enables rapid and easy estimation of the consequences of abatement at one stage of manure management (upstream) at later stages (downstream). Such a model enables scenario analysis of abatement options and cost-curve production. The approach provides an unbiased assessment of the costs of abatement so that priority can be given to the most cost-effective measures.

The resulting cost-curve analysis indicates that these are generally the rapid incorporation of slurry or litter-based manures (FYM) into arable land, and the application of slurry to grassland by trailing shoe or injection equipment. These methods rank highly because of their large potential for abatement (60-90% of NH₃ emissions), relatively small cost and because once manure is incorporated into soil there is little further potential for abatement. Some approaches earlier in manure management may also be cost-effective. In particular allowing the surface of slurry stores to congeal (crusting) and storing FYM prior to spreading instead of spreading to land immediately the manure is removed from buildings. However, the adoption of even the most cost-effective measures may have serious adverse effects on farm budgets. The costs need to be assessed against affordability.

There is a need to ensure that measures taken to reduce emissions of NO_x and NH₃ do not, so far as possible, increase other emissions of reactive-N. Early indications from modeling studies in the UK indicate that significant redustions in NH₃ emissions can be obtained while leading to only small total increases in nitrate leaching. However, locally abatement may lead to significant increases in nitrate concentrations in water. A group of modelers are working together in Europe to produce a harmonised TAN-flow model, and to produce simple integrated, N and C mass-flow approaches for all gaseous emissions from livestock excreta

⁽¹⁾ ADAS Research, Woodthorne, Wergs Road, Wolverhampton WV6 8TQ, UK, Telephone: +44 1902 693235, Fax +44 1902 693166, E-mail: stubweiss@netscape.net
⁽²⁾ Federal Agricultural Research Centre, Braunschweig, Germany
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