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 (NH₃), the focus of this paper is on N lost as NH₃ 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 NH₃-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 NH₃ emissions and NUE. The results showed that the animal product with the lowest NUE had the largest NH₃ emissions and vice versa, which agrees with the reciprocal relationship between NUE and NH₃ within the conceptual framework. Across animal products for the countries considered, about 20% of the N in feed is lost as NH₃. The significant smallest proportion (12%) of NH₃-N per unit of Nfeed 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 NH₃-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 NH₃. The production of 1 kg N in milk required 4 kg N in feed with 0.6 kg NH₃-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 NH₃ emission inventories.

Keywords: Ammonia emission intensity; Animal protein; Feed nitrogen; Manure management; Nitrogen use efficiency.

Graphical abstract

Fig. 1

Conceptual framework of how nitrogen in feed (N Feed) is transformed into emission of nitrogen as ammonia (NH₃—N) and nitrogen in product (N Product); d = apparent digestibility of feed, p = proportion of N metabolised deposited in product, f = feed waste, m = fraction of organic N in manure mineralised to TANmin (Total Ammoniacal Nitrogen mineralised), TANex = TAN excreted, e = fraction of total TAN emitted as NH₃—N.

Fig. 2

Protein deposition, nitrogen use efficiency (NUE) and ammonia (NH₃—N) emission related to digestible protein in feed. FPM and FPP are digestible feed protein at maintenance level and potential production level respectively. The solid red line is NH₃—N emission per kg protein deposition (EI), the solid green line is NUE (no dimension), and dotted red lines are lower or higher NH₃—N emission due to factors related to manure management.

Fig. 3

Relationship between AEI (NH₃—N/N in product) and NUE for 5 livestock products of 6 European countries (The Netherlands, Switzerland, United Kingdom, Germany, Austria and Denmark). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 4

Relative contribution of manure management (EF) to NH₃ (NH3_MMS) versus that of TAN excretion (NH3_TANex) for milk, beef, pork, eggs, and chicken in the six different countries NL (light blue), CH (red), UK (green), DE (dark blue), A (yellow), DK (orange); a: low TAN, high EF; b: high TAN, high EF; c: high TAN, low EF; d: low TAN, low EF. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)