This measure is implemented at farm level and can be encouraged through policy or emission constraints.
This measure can potentially be combined with a number of others such as animal house adaptation (SA), covered outdoor storage of manure (CS), and low ammonia application (LNA) (links). Furthermore, removal efficiencies are calculated for four emission stages – housing, outside storage, application, and grazing. Removal efficiencies also vary depending on the type of animal. Thus given the range of other measures with which this measure can be combined, as well as the range of methods that potentially can be adopted for specific animal types, the impact on resulting ammonia emissions can vary across quite a wide range.
It is estimated that LNF (when not combined with any other measure) can remove approximately between 10% - 20% of NH3 emissions depending on the type of livestock and method adopted. However, this proportion will increase significantly if combined with other measures (for example, 76% when combined with SA and LNA for poultry).
Furthermore there are also potential knock-on effects of several ammonia measures on other pollutants such as methane (CH4) and nitrous oxide (N2O). Emissions of CH4 are influenced by the daily feed intake and the digestibility rate, but they do not directly depend on the nitrogen content of the feed (IPCC, 1997). However, these factors may be affected by changes in the nitrogen content of the feed, which, in turn, may result in different levels of CH4 emissions from enteric fermentation and from manure management. Since it is not clear to what extent and in what direction reductions in the nitrogen content of the fodder will affect CH4 emissions, it is tentatively assumed that there is no effect on CH4.
N2O emissions depend on the amount of nitrogen excreted by animals. A lower nitrogen content of the fodder reduces the nitrogen excretion per animal and, as a consequence, N2O emissions from livestock (assuming a constant livestock population). While emissions of NH3 only depend on the mineral nitrogen in the manure, N2O emissions also depend on the organic nitrogen in the manure. Use of low nitrogen feed will result in lower amounts of mineral nitrogen, while organic nitrogen in the manure will be less affected. Therefore, the reduction rate for N2O emissions may differ from the rate for NH3. The extent of the reduction of N2O emissions is not fully understood as of yet, however.
Modelling this measure can be achieved through the use of the GAINS model. Essentially assumptions regarding the adoption and share of a given control are made by national experts. GAINS then combines these assumptions with national energy forecasts and abated emission factors (i.e. inclusive of the removal efficiencies of the given control) and provides resulting emissions estimates. This provides modelled effects of this measure as compared to the level of emissions if this measure was not in place.
Furthermore, as with other agricultural measures it is possible to model the effects of this measure either on its own, or when combined with others (such as animal house adaptation, covered storage, and low ammonia application, for example).
Klimont, Z. and Brink, C. (2004) ‘Modelling of emissions of air pollutants and greenhouse gases from agricultural sources in Europe’, IIASA Interim Report IR-04-048, Laxenburg
IPCC (1997) ‘Revised 1996 IPCC guidelines for national greenhouse gas inventories’, Organisation for Economic Co-operation and Development (OECD), Paris