This dataset contains N2O isotopic source signatures obtained from Keeling analysis of measured singly substituted isotopologues of N2O (δ15Nα, δ15Nβ, δ18O) along with calculated weekly averaged greenhouse gas fluxes of N2O, CH4 and CO2 at the Demo trial field site, located at the Agroscope Reckenholz Research Station in Zürich, Switzerland. The data was collected in a long-term crop rotation and fertilisation experiment that investigates the effects of nutrient availability on crop development and soil emissions. Fluxes were measured weekly using an automatic time integrating chamber (ATIC) system, with subsequent analysis of gas concentrations and isotopologues performed using high-precision commercial analysers (Picarro G5131-i (2x) and Picarro G2401 (1x)). The dataset provides high-resolution time series of gas fluxes and isotopic source signatures under different fertiliser treatments (NPK and null treatment), with a focus on sugar beet cultivation during the study period. These data are intended to support research on agricultural greenhouse gas emissions, soil microbial processes, and fertilisation management impacts. Please see the readme files in the archive for detailed information about the dataset contents and preview images.