Vegetable production systems with excessive nitrogen fertilizer result in severe N2O emission. It is pivotal to identify the source of N2O for reducing N2O emission, but estimating microbial pathways of N2O production is very difficult due to the existence of N2O reduction. A promising tool can address this problem by using δ18O and δ15NSP of N2O to construct a dual isotopocule plot. For ascertaining the microbial pathways of N2O production and consumption in soil fertilized for vegetable production, four treatments were set up: urea (U), half urea and half organic fertilizer (UO), organic fertilizer (O) and no fertilizer (NF), and the experiment was carried out continuously for two years. The δ18O vs. δ15NSP plot method indicated that the nitrification/fungal denitrification was a dominant in N2O emission, and the U treatment was the highest, followed by OU, O and NF in the both years. Among the different treatments, furthermore, the N2O flux had the same trend, whereas the extent of N2O reduction showed an opposite trend. Overall, inorganic fertilizer enhances nitrification/fungal denitrification and hinders reduction of N2O to N2, resulting in a larger amount of N2O emission. However, organic fertilizer increases the contribution of denitrification and greatly improves the extent of N2O reduction, which helps to reduce N2O emission. Therefore, organic fertilizer is crucial to reducing N2O emission by enhancing N2O reduction and should be properly applied in production practice.
Keywords: Dual isotopocule plot; Microbial processes; N(2)O reduction; Organic fertilizer; Vegetable production.
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