Abstract

Nitrogen mineralization (NM) is a microbially mediated process that controls the conversion of soil organic nitrogen (N) into plant-available forms and, therefore, governs N supply. In hazelnut (Corylus avellana), NM operates under seasonal regulation and strongly constrained by soil physiochemistry, particularly in volcanic temperate soils where high organic matter content, organo-mineral associations, and acidity can decouple gross transformation potential from net N availability. This review synthesizes scientific evidence published over the last ten years (2016-2026) on the factor and mechanisms regulating NM in hazelnut planted under temperate conditions, emphasizing the role of microbial guilds and enzyme-mediated transformations that determine the balance between mineralization, immobilization, and N losses. Key biochemical mediators linked to root exudation and microbial metabolism to pH regulation, nutrient mobilization, and shifts in microbial community composition, influencing the proportion and dynamics of NH4 + and NO3 & horbar; available. We discussed diagnostic frameworks and evidence-based assessment tools, including tissue-based thresholds, fertilization trials, and isotopic approaches (e.g., & sup1;N-5 tracers), which collectively support improved nitrogen use efficiency (NUE) through better synchronization of N supply and crop demand. Fertilization management of hazelnut includes the potential of soil-conserving practices, diversification strategies, and biologically oriented approaches to enhance soil biology, strengthen internal N cycling, and environmental impact reduction associated with synthetic N inputs in hazelnut. Literature on NM and hazelnut relationship is very scarce, mainly associated to input of synthetic fertilizers but without an overview of N availability in soils. As hazelnut cultivation continues to expand into volcanic soils, mechanism-based on understanding of N cycling becomes crucial by integrating microbiological, edaphic, and agronomic perspectives is essential to optimize N availability and NUE, particularly under the complex and variable conditions typical of temperate climates.