Optimizing nitrogen use efficiency in European livestock systems: From feed to plant growth

Nitrogen (N) is a crucial nutrient for agriculture. Its unlimited provision by the Haber-Bosch process has led to high N surplus in agriculture, causing severe negative environmental externalities. The reduction of N losses in livestock systems and consequent enhancement of their nitrogen use efficiency (NUE) represents a key lever to substantially reduce the N surplus to meet European environmental policy targets. This review evaluates the potentials to improve the NUE of European cattle and pig livestock systems from feed to plant N use along the whole livestock system cascade. It discusses options to improve feed NUE and the current measures to reduce N losses at housing, manure storage and application as well as crop N recovery. The findings are synthesized at the overall livestock system level using exemplary case-study farms from selected European regions, to highlight potentials for livestock system NUE improvements in the context of the current and future European legislations. All case-study farms have already implemented measures for N loss mitigation, and their livestock system NUE reaches values between 55 % and 75 %. With the implementation of additional measures such as liquid manure acidification, low emission technologies and best field management, livestock system NUE can reach values between 75 % and 85 %. In order to achieve such high livestock system NUE and meet environmental goals, a scaled implementation of best available technologies is essential, and has to go hand in hand with a legislative harmonization and a targeted development of additional reduction measures and auxiliary tools for farmers.