Globally, 50-70% of the N fertilizer applied to cropping systems is lost as nitrate and N-oxides, raising agricultural production costs and contributing to environmental pollution and climate change. These losses are directly linked to the nitrification process catalysed by soil nitrifying microbes. The mitigation of reactive nitrogen (Nr) loss via nitrification inhibitors (NIs) is a promising solution for increasing N use efficiency (NUE) in agriculture. ACTIONr aims to unravel the scientific excellence and innovation potential of a Widening country (Greece), through a European network of excellence on establishing novel tools and pathways for optimized NUE, reducing the continued acceleration of the N cycle, and decreasing the environmental footprint of Nr. As a centre for Greek agricultural production, Thessaly is suited to serve as a model for research on microbial N transformations for optimizing NUE in agroecosystems, but local capacity is not fully explored yet. Twinning of UTH with two internationally leading partners in Ecogenomics (UNIVIE) and Microbial Ecology (ECL) of the soil N cycle will: (i) further develop research excellence of UTH, (ii) improve its networking efficiency and interdisciplinarity, and (iii) have broad societal and environmental impact towards more efficient N management in agricultural settings.