Partitioning of sources of N2O from soil treated with different types of fertilizers by the acetylene inhibition method and stable isotope analysis

Abstract

Nitrous oxide (N2O) 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 N2O in agricultural soils, especially in vegetable production, where large amounts of nitrogen fertilizers are commonly used. Isotopomer ratios of N2O, oxygen and bulk nitrogen isotope values (δ18O and δ15Nbulk) and intramolecular 15N site preferences (SP) have recently been used to identify the sources of N2O. In this study, vegetable farm soil was incubated with manure (M), compound fertilizers (CF) and no fertilizers (NF). The acetylene inhibition method and a 15N isotopic technique were used to reveal the most likely microbial processes leading to N2O emissions. The results showed that the M treatment produced smaller N2O emissions than the CF treatment of the soil. Nitrifier denitrification or denitrifier denitrification made the greatest contribution to N2O production in the M treatment, accounting for approximately 60–89% of N2O production, whereas it was 25–55% and 37–66% in the CF and NF treatments under non‐acetylene conditions, respectively. Under non‐acetylene conditions, N2O reduction to N2 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 N2O 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 N2O with SP would be a practical approach for determining the contributions of microbial processes to N2O emissions from different pools in soil. The results revealed that manure produced smaller N2O emissions and promoted relatively larger rates of denitrification and N2O reduction than compound fertilizers with the same amount of N, which indicated that complementing chemical with manure fertilizers might help to reduce N2O emissions on vegetable‐producing land.Highlights We investigated emissions and sources of N2O with different types of fertilizers. For the same amount of N, manure produced less N2O than compound fertilizer. Stable isotope analysis revealed that denitrification was the dominant process in the manure treatment. The acetylene inhibition method can supplement δ15Nbulk compared with the SP model to assess N2O reduction in soil.