Comparison of ammonia emissions related to nitrogen use efficiency of livestock production in Europe

Abstract

The increasing global demand for food and the environmental effects of reactive nitrogen losses in the food production chain, increase the need for efficient use of nitrogen (N). Of N harvested in agricultural plant products, 80% is used to feed livestock. Because the largest atmospheric loss of reactive nitrogen from livestock production systems is ammonia (NH ₃), the focus of this paper is on N lost as NH ₃ during the production of animal protein. The focus of this paper is to understand the key factors explaining differences in Nitrogen Use Efficiency (NUE) of animal production among various European countries. Therefore we developed a conceptual framework to describe the NUE defined as the amount of animal-protein N per N in feed and NH ₃—N losses in the production of milk, beef, pork, chicken meat and eggs in The Netherlands, Switzerland, United Kingdom, Germany, Austria and Denmark. The framework describes how manure management and animal-related parameters (feed, metabolism) relate to NH ₃ emissions and NUE. The results showed that the animal product with the lowest NUE had the largest NH ₃ emissions and vice versa, which agrees with the reciprocal relationship between NUE and NH ₃ within the conceptual framework. Across animal products for the countries considered, about 20% of the N in feed is lost as NH ₃. The significant smallest proportion (12%) of NH ₃—N per unit of N feed is from chicken production. The proportions for other products are 17%, 19%, 20% and 22% for milk, pork, eggs and beef respectively. These differences were not significantly different due to the differences among countries. For all countries, NUE was lowest for beef and highest for chicken. The production of 1 kg N in beef required about 5 kg N in feed, of which 1 kg N was lost as NH ₃—N. For the production of 1 kg N in chicken meat, 2 kg N in feed was required and 0.2 kg was lost as NH ₃. The production of 1 kg N in milk required 4 kg N in feed with 0.6 kg NH ₃—N loss, the same as pork and eggs, but those needed 3 and 3.5 kg N in feed per kg N in product respectively. Except for beef, the differences among these European countries were mainly caused by differences in manure management practices and their emission factors, rather than by animal-related factors including feed and digestibility influencing the excreted amount of ammoniacal N (TAN). For beef, both aspects caused important differences. Based on the results, we encourage the expression of N losses as per N in feed or per N in product, in addition to per animal place, when comparing production efficiency and NUE. We consider that disaggregating emission factors into a diet/animal effect and a manure management effect would improve the basis for comparing national NH ₃ emission inventories.

Graphical abstract

Highlights

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  A theoretical framework describes NH ₃—N loss and NUE related to animal protein production instead of to raw product.

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  Animal protein in chicken meat had the highest NUE and the lowest NH3—N losses; the reverse was true for beef.

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  Differences in NUE and NH3—N losses between countries are mainly explained by manure management.

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  For beef production differences in manure management and TAN production are both relevant.

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  Presenting additional metrics than N-lost per animal place would enable a more informed comparison of production systems.