A model for inventory of ammonia emissions from agriculture in the Netherlands

Agriculture is the major source of ammonia (NH3). Methodologies are needed to quantify national NH3 emissions and to identify the most effective options to mitigate NH3 emissions. Generally, NH3 emissions from agriculture are quantified using a nitrogen (N) flow approach, in which the NH3 emission is calculated from the N flows and NH3 emission factors. Because of the direct dependency between NH3 volatilization and Total Ammoniacal N (TAN; ammonium–N + N compounds readily broken down to ammonium) an approach based on TAN is preferred to calculate NH3 emission instead of an approach based on total N. A TAN-based NH3-inventory model was developed, called NEMA (National Emission Model for Ammonia). The total N excretion and the fraction of TAN in the excreted N are calculated from the feed composition and N digestibility of the components. TAN-based emission factors were derived or updated for housing systems, manure storage outside housing, manure application techniques, N fertilizer types, and grazing. The NEMA results show that the total NH3 emission from agriculture in the Netherlands in 2009 was 88.8 Gg NH3–N, of which 50% from housing, 37% from manure application, 9% from mineral N fertilizer, 3% from outside manure storage, and 1% from grazing. Cattle farming was the dominant source of NH3 in the Netherlands (about 50% of the total NH3 emission). The NH3 emission expressed as percentage of the excreted N was 22% of the excreted N for poultry, 20% for pigs, 15% for cattle, and 12% for other livestock, which is mainly related to differences in emissions from housing systems. The calculated ammonia emission was most sensitive to changes in the fraction of TAN in the excreted manure and to the emission factor of manure application. From 2011, NEMA will be used as official methodology to calculate the national NH3 emission from agriculture in the Netherlands.