Distinguishing N₂O and N₂ ratio and their microbial source in soil fertilized for vegetable production using a stable...

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 δ¹⁵N^SP 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. δ¹⁵N^SP 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.