【Objective】Denitrification in agricultural soils is jointly regulated by the quantity and quality of organic carbon materials. This study aimed to reveal how organic materials of different quality affect denitrification-derived gaseous nitrogen (N) emissions and the N2O/(N2O+N2) product ratio in typical agricultural soils, and to elucidate the underlying mechanisms. 【Method】Paddy soil from a rice–wheat rotation field and greenhouse vegetable soil in the Taihu Lake region were collected as test soils, to which six types of exogenous organic carbon with contrasting C/N ratios were applied. The treatments include wheat (WS), rice (RS) and maize straw (MS) and their corresponding biochars (WSB, RSB, and MSB). In parallel, the respective straw- and biochar-derived leachates (LWS, LRS, LMS, LWSB, LRSB, and LMSB) were added, and a Robot automatic gas analysis system, qPCR and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were employed to quantify gaseous N emissions and the N2O/(N2O+N2) product ratio, denitrification functional genes, and the molecular composition of dissolved organic matter (DOM) in the leachates.【Result】The results showed that, in paddy soil, both straw and biochar increased the abundances of nirS and nirK, leading to significantly higher cumulative N2O emissions and N2O/(N2O+N2) ratios. Their leachates similarly enhanced N2O production, with LMS showing the greatest increase of 242.4%. Straw and its leachates exhibited substantially higher (nirS+nirK)/nosZ ratios than biochar and its leachates, corresponding to higher N2O/(N2O+N2) ratios. In vegetable soil, straw and biochar also increased N2O emissions, and this effect was further pronounced when their leachates were applied. The LWS treatment showed the greatest cumulative N2O emission (268.57 mg kg?1) and an N2O/(N2O+N2) ratio of 0.87, attributable to high background NO3?-N, which suppressed nosZ abundance and N2O reduction. FT-ICR MS revealed that straw-leached dissolved organic matter (DOM) was dominated by recalcitrant lignin-like and condensed aromatic compounds, which accounted for 88.43%, 86.90% and 85.03% of the DOM molecular abundance in LWS, LRS and LMS, respectively. The increase in relative abundance of condensed aromatics and the aromaticity index (AImod) significantly (P < 0.05) increased both N2O emissions and the N2O/(N2O+N2) ratio. In contrast, biochar-leached DOM contained more labile lipid-like and protein/amino sugar-like compounds, and the relative abundance of protein/amino sugar molecules was positively associated with cumulative N2 emission (P < 0.05). 【Conclusion】In summary, the qualitative properties of organic carbon inputs are a key determinant of denitrification rates and the partitioning of gaseous N products in agricultural soils. Therefore, optimizing organic material inputs to regulate the chemical composition of soil organic carbon, together with coordinated control of pH and NO3?-N levels, is critical for achieving high NO3?-N removal efficiency while minimizing the N2O/(N2O+N2) ratio. This, in turn, promotes the conversion of denitrification end-products toward N2, thereby facilitating reactive N mitigation and sustainable N cycling in agroecosystems.