Primed N2O emission from native soil nitrogen: A 15N‐tracing laboratory experiment

AbstractSoils can naturally be a source of the potent greenhouse gas nitrous oxide (N2O). By contrast, the largest anthropogenic source of N2O is the application of nitrogen (N) fertilizer on agricultural soil, but it is unclear if fertilizer‐supported N2O emission only originates from the fertilizer N directly or through additionally stimulated N2O production from native soil N. Even though native soil N also includes mineral N already in soil before fertilizer application, organic N is the principal native N pool and thereby provides for mineral N cycling and N2O emission. Here, we tested (1) the contribution of native soil N to N2O emission after mineral N fertilizer application and (2) whether it is affected by different soil organic matter (SOM) contents by conducting a laboratory 15N‐tracing experiment with agricultural soil from a long‐term field trial with two treatments. Both field treatments are fertilized with mineral N, whereas only one of the two receives liquid manure causing higher SOM content. Soil sampling was conducted in March 2016 shortly before fertilizer application in the field. The application of 15N‐labeled fertilizer more than doubled the N2O production from native N sources compared to the non‐fertilized control incubations. This primed N2O production contributed by 5–8% to the fertilizer‐induced N2O emission after one week of incubation and was similar for both field treatments regardless of liquid manure application. Therefore, further research is needed to link N2O priming to its potential production pathways and sources. While the observed effect may be important in soils, the amount of applied N fertilizer remains the largest concern being responsible for the majority of N2O emission.