Over the last few decades, intensified agricultural production has greatly increased fluxes of nitrogen (N) between different compartments of the biosphere, and more specifically, emissions of N compounds from agroecosystems. Agriculture is one of the main emitters of N compounds (e.g. ammonia, nitrate, nitrous oxide) whith negative impact on the environment like greenhouse-gas emissions and contamination of surface and ground water. Greater efficiency in N-fertiliser use and the reduction of environmentally harmful N losses are therefore still urgent matters of concern for most industrial countries. New technologies such as anaerobic fermentation (AF) of slurry combined with subsequent ultrafiltration (UF) and reverse osmosis (RO) can be attractive options for agriculture, potentially enabling to optimise nutrient management, reduce volumes of transported slurry, and generate renewable energy. In this study, anaerobically fermented pig slurry and fertilizer products from the subsequent mechanical separation (UF and RO) were characterised and their apparent N-use efficiency determined in pot and field experiments by means of the difference method. Treatment of pig slurry with AF, UF and RO increased the ammonium N concentration, which improved plant N availability. Since the pH value also increases in parallel during treatment, the risk of gaseous losses during storage and application also rises. Nevertheless, new slurry-treatment technologies coupled with low-emission application techniques (e. g. spreader with trailed hoses) can potentially both increase the N efficiency of slurry and reduce N emissions to the environment.