Substituting Chemical Fertilizer with Chicken Manure Alters Soil Dissolved Organic Matter and Volatile Organic Compound Profiles in Chinese Cabbage

Reducing chemical fertilizer (CF) dependence through animal manure substitution is critical for sustainable agriculture, but its impact on vegetable volatile organic compound (VOC) profiles remain unclear. Here, we investigated how chicken manure (CM) substitution rates affect soil carbon/nitrogen dynamics and VOC profiles in Chinese cabbage. Five fertilization treatments were conducted: group A (no fertilizer inputs), group B (CF inputs alone), and groups C, D and E (substituting 33.3%, 66.6%, 100% of group B’s chemical nitrogen rate with CM). Soil dissolved organic matter (DOM) was characterized using UV–visible and excitation-emission matrix spectroscopy. VOCs were analyzed by headspace gas chromatography–time-of-flight mass spectrometry. Relationships between VOC profiles and soil DOM characteristics were assessed using Random Forest and Partial Least Squares Path Modeling (PLS-PM). Compared to group B, groups C and D maintained higher nitrogen accumulation. Groups C, D, and E exhibited increased soil total nitrogen, dissolved organic carbon, and enhanced DOM hydrophobicity, aromaticity, humus, and terrestrial humus-like content relative to group B. However, groups D and E exhibited significantly less total VOCs and ester concentrations than group B. Correlation and PLS-PM analyses revealed that DOM parameters directly and negatively impacted total VOC content (p ≤ 0.05). While DOM characteristics explained the total VOC decrease, they did not account for reduced esters under CM, suggesting potential microbial community shifts as an additional factor. A CM substitution rate of 33.3% balanced agronomic performance, environmental benefits and preserved Chinese cabbage sensory quality, offering a viable pathway for CF reduction.