Fertilizer-N recovery links to SOC stabilization and fractionation in straw-mulched soil: Insights from 15N-tracing and 13C natural abundance

While straw mulching has the potential to reduce fertilizer-nitrogen (N) losses in intensively managed cropland, how soil organic carbon (SOC) regulates this fate of fertilizer-N at soil aggregate or profile scales remains unresolved. Here, micro-plots were nested within a four-year field experiment to assess fertilizer-N fates and their linkages with SOC fractions and stabilization processes via 15N-tracing and 13C natural abundance analyses. Three treatments were included: (i) conventional N application (FN), (ii) reduced N application (RN), and (iii) reduced N with straw mulching (RS). While RN reduced crop yields compared to FN, RS achieved comparable yields and 7.71% higher N recovery efficiency (P2 mm and