Partitioning of sources of N 2 O from soil treated with different types of fertilizers by the acetylene inhibition method and stable isotope analysis

Nitrous oxide (N 2 O) is one of the major human‐induced greenhouse gases. It has a large potential for global warming, a long lifetime and can deplete ozone. In China, nitrogenous fertilizer is an important source of N 2 O in agricultural soils, especially in vegetable production, where large amounts of nitrogen fertilizers are commonly used. Isotopomer ratios of N 2 O, oxygen and bulk nitrogen isotope values ( δ 18 O and δ 15 N bulk ) and intramolecular 15 N site preferences (SP) have recently been used to identify the sources of N 2 O. In this study, vegetable farm soil was incubated with manure (M), compound fertilizers (CF) and no fertilizers (NF). The acetylene inhibition method and a 15 N isotopic technique were used to reveal the most likely microbial processes leading to N 2 O emissions. The results showed that the M treatment produced smaller N 2 O emissions than the CF treatment of the soil. Nitrifier denitrification or denitrifier denitrification made the greatest contribution to N 2 O production in the M treatment, accounting for approximately 60–89% of N 2 O production, whereas it was 25–55% and 37–66% in the CF and NF treatments under non‐acetylene conditions, respectively. Under non‐acetylene conditions, N 2 O reduction to N 2 was largest for treatment M (32–90%), intermediate for NF (42–77%) and smallest for CF (20–51%). The results also showed that nitrifier nitrification and N 2 O reduction were partly inhibited under acetylene conditions, with a relative contribution of 9–20% and 0–83% for M, 39–48% and 0–46% for CF, and 25–35% and 0–56% for NF, respectively. Our results suggest that analysing isotopomer ratios of N 2 O with SP would be a practical approach for determining the contributions of microbial processes to N 2 O emissions from different pools in soil. The results revealed that manure produced smaller N 2 O emissions and promoted relatively larger rates of denitrification and N 2 O reduction than compound fertilizers with the same amount of N, which indicated that complementing chemical with manure fertilizers might help to reduce N 2 O emissions on vegetable‐producing land. Highlights We investigated emissions and sources of N 2 O with different types of fertilizers. For the same amount of N, manure produced less N 2 O than compound fertilizer. Stable isotope analysis revealed that denitrification was the dominant process in the manure treatment. The acetylene inhibition method can supplement δ 15 N bulk compared with the SP model to assess N 2 O reduction in soil.