Evaluation of N2O sources after fertilizers application in vegetable soil by dual isotopocule plots approach.

Nitrogen (N) fertilizer is the major deriver of nitrous oxide (N 2 O) emissions in agricultural soil. In the vegetable fields in China both inorganic and organic fertilizers are largely applied as basic sources of nitrogen. Identifying the effects of fertilizer type on soil microbial activities involved in N 2 O emissions would be of great help for future development of N 2 O reduction strategies. N 2 O isotopocule deltas, including δ 15Nbulk, δ 18O and SP (the 15N site preference in N 2 O), have been used to analyze microbial pathways of N 2 O production under different treatments, including bio–organic fertilizer treatment, half bio–organic fertilizer and half urea (mixed fertilizer) treatment, urea treatment and no fertilizer treatment. We measured environmental factors, N 2 O fluxes and N 2 O isotopocule deltas to evaluate the dynamics of N 2 O emissions and constructed the dual isotopocule plots (δ 15Nbulk vs. SP and δ 18O vs. SP) of the main N 2 O emission phases to assess contribution of the involved microbial processes (bacterial nitrification, bacterial denitrification, nitrifier denitrification and fungal denitrification). According to the results of the main N 2 O emission phases, we found that bio–organic fertilizer and mix fertilizer treatments had significantly lower N 2 O emissions compared to urea treatment, with average N 2 O fluxes of 1477 ± 204, 1243 ± 187 and 1941 ± 164 μg m−3 h−1, respectively, but there were no significant effects on mineral N and cabbage yield. In addition, the urea treatment and the mixed fertilizer treatment had close and higher nitrogen use efficiency. Furthermore, the δ 18O vs. SP plot was useful for providing insight into microbial processes, showing that fungal denitrification/bacterial nitrification was the dominant microbial pathway and bio–organic fertilizer and mix fertilizer treatments had higher denitrification and N 2 O reduction compared to urea treatment. Those findings demonstrated that the partial replacement of urea with bio–organic fertilizer was a better choice, by means of enhancing denitrification to reduce N 2 O emissions and also guaranteeing the nitrogen use efficiency and the cabbage yield. • The partial replacement of urea with bio–organic fertilizer was a better choice to reduce N 2 O emissions. • Compared with the δ 15Nbulk vs. SP plot, the δ 18O vs. SP plot provided a clearer insight into N 2 O production pathways. • Fungal denitrification might be dominant microbial pathway for all treatment in our study. [ABSTRACT FROM AUTHOR]