Indicators to evaluate agricultural nitrogen efficiency of the 27 member states of the European Union
Introduction
The European Union (EU) is one of the most intensive agricultural regions per unit of surface area (Haberl et al., 2007, Monfreda et al., 2008). This productivity is supported by the massive use of agricultural inputs, mostly nitrogen (N) fertilizers (Mueller et al., 2012) and imported feedstuff (Lassaletta et al., 2014). However, only 31% of agricultural N inputs are recovered in intended products at the European scale (Leip et al., 2011b). This low N efficiency results in major N losses, which have problematic impacts on water, air and soil quality as well as ecosystem functions, biodiversity and human health (Sutton et al., 2011). Rockstrom et al. (2009) identified the disruption of the biogeochemical N cycle as one of the main threats to future human development. Improving N efficiency, defined as the ratio between N in intended agricultural products and N used to produce them, is crucial to reduce this environmental impact while also providing enough food, feed, fuel and fiber to the growing population (Sutton et al., 2011).
The territory scale is a particularly important research challenge. It integrates all biogeochemical flows and provides additional solutions compared to those at smaller scales (e.g. manure exchange, landscape management, wastewater treatment). It allows analysis of specific national agricultural trends and policies, such as the EU Common Agricultural Policy (Velthof et al., 2014) to prioritize actions that limit environmental risks (Leip et al., 2011a). Indicators that quantify N efficiency are necessary to improve it at the territory scale.
Most N management indicators at the territory scale focus on estimating N losses through modeling approaches (Moreau et al., 2013) or N balances such as the farm-gate balance (FGB; Dalgaard et al., 2012). N footprint indicators (Galloway et al., 2014) have also been developing recently. They consider the whole food chain (input and food production, food processing and consumption), and can include other human activities such as energy use. The most used N efficiency indicator is called nitrogen use efficiency (NUE; Leip et al., 2011b, Liu et al., 2008). This indicator is recommended as an agro-environmental indicator for the Common Agricultural Policy (European Commission, 2000). The United Nations Economic Commission for Europe considers it a legal tool for implementing the Gothenburg Protocol on air pollution (UNECE, 2012). However, both FGB and NUE have several limitations:
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Considered inputs and outputs can vary depending on the boundaries and definitions used by the authors. For instance, manure output can be considered an output, a negative input or is ignored in indicators calculation (Dalgaard et al., 2012, Simon et al., 2000, Spears et al., 2003)
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N emitted during production and transport of inputs is not always included (Schröder et al., 2003, Sutton et al., 2013)
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changes in soil N are rarely considered in the calculation of indicators due to the lack of data (de Vries et al., 2011, Özbek and Leip, 2015)
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NUE is calculated as a ratio between N outputs and inputs. Thus, if the same quantity of N is added on both input and output sides, the ratio tends towards one. This mathematical bias favors farms that buy animal feed and sell crops against those that feed their animals with their crops (Godinot et al., 2014, Schröder et al., 2003).
A novel indicator, system nitrogen efficiency (SyNE; Godinot et al., 2014), is based on NUE but resolves its limitations. SyNE presents some similarities with existing N footprint indicators, but focuses on the efficiency of agricultural systems to transform N inputs into intended N outputs, while N footprint indicators usually focus on N losses due to the consumption patterns of end-consumers. Similarly, system nitrogen balance (SyNB; Godinot et al., 2014) is based on FGB and resolves its limitations. As the novel indicators are based on existing indicators that have been used at the territory scale, they should also be applicable to this scale.
Several authors claim that N efficiency is linked to the type of production system considered (Schröder et al., 2003, UNECE, 2012). By nature, a farming system or a territory with mostly animal production will be less efficient than a system with mostly crops. The relative nitrogen efficiency (RNE) indicator addresses these biological differences by expressing efficiency relative to the maximum attainable efficiency of each product (Godinot et al., 2015).
The goal of this study was to apply the three indicators presented above (SyNE, SyNB and RNE) to the 27 member states of the EU to test their ability to describe N management at the territory scale and each member state's progress margin in N efficiency.
Section snippets
Indicator calculation
SyNE, SyNB and RNE were calculated at the national scale, as follows:where: is the sum of the n net N outputs by crops and animal products, is the sum of the m net N inputs from organic and inorganic fertilizers, feed, seeds, manure,
National N flows
Fig. 2 and Table 2 present the mean annual N flows for each of the EU-27 member states for the 2000–2008 period. All means calculated in this work are unweighted arithmetic means, in order to compare countries to a collective reference with no effect of size. Mean net animal output was 22 kg N ha−1 AA and ranged from 4 to 108 kg N ha−1 AA. Mean net crop output was 11 kg N ha−1 AA and ranged from 0 to 32 kg N ha−1 AA. During this period, 10 member states had net outputs composed of over 60% animal products.
Conclusion
This study demonstrates the feasibility and utility of calculating N efficiency and balance indicators at the national scale. The three indicators developed (SyNE, SyNB and RNE) are not directly comparable to existing references due to methodological differences but are consistent with them. The indicators are calculated according to a systems approach that includes activities upstream of agricultural production (from cradle to farm gate). This integrative approach enables relevant comparisons
Acknowledgements
The authors are grateful to Michelle and Michael Corson for English proofreading. They also thank two anonymous reviewers whose comments and suggestions improved this manuscript.
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